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BB Proof 2A3 DC

108.168.121.47
Posted on December 5, 2014 at 20:22:08
Garg0yle
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Posts: 859
Joined: December 1, 2014
 This is a continuation thread branched from a previous discussion here:
http://www.audioasylum.com/cgi/vt.mpl?f=set&m=77251

Paul generously offered to conjure up a schematic for us to use.

Here are tentative parameters for this amp:

Octal driver
2A3 output
Tube rectifier
Direct coupled

Readily-available (Hammond) iron
Relatively reliable (BB-proof?)
Uncomplicated - no special tricks
No solid-state components
Monoblocks

I am going to list the specs parts I already have here for use here:

PT 370-340-0-340-370 Includes windings for a 2.5V/3.5V, and two 5V/6.3V windings. In hindsight it would have been better to have separate filament transformers.

OPT is 2.5K/3.5K with 4/6/8 ohm secondaries.

Chokes are two x 7.5H @ 160ma or one x 30H @80ma.

I have two of everything for monoblocks.

Mr. Joppa kindly offered this help as a Public Domain type of project so I wont be offended if anyone wants to jump in with questions of their own.

My chassis are close to being finished. I have to decide if I need to put just one or two switches on it. The second switch could potentially be a provisional switch for a delayed start was my thinking.

I have the 2A3's, but no octal input tubes. I have an assortment of electrolytic and resistors, but may have to get more depending on what is needed. I'm good in the wire department.

I had done some preliminary tinkering with PSUD and can get a solid 130 micro-volts ripple @ 419V with a CLCLC and a 5V4.
I also had a CLC that I recall being decent, but I must have mislabeled it when saving.

I might also try to build this in spice as a parallel project, but I won't let it distract me from the physical build.
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What octals?, posted on December 6, 2014 at 01:59:27
Frihed89
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Posts: 15703
Location: Copenhagen
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 What are the possibilities to replace something like 1/2 a 12Ax7 per channel? With cap coupled 2A3 amps, the octal choices are quite large.

I am asking from ignorance, only.

 

octal possibilities, posted on December 6, 2014 at 05:59:47
Jim Dowdy
Manufacturer

Posts: 1518
Location: Atlanta, GA
Joined: July 22, 2000
 Assuming you are sticking with triodes, the 6SF5, 2C52, and 6SL7 are all possibilities.

 

RE: What octals?, posted on December 6, 2014 at 06:51:14
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005
 You are best served with a mu of 70 to 100 tube, driving a DHT Type 45 or a 2A3. I prefer mu of 100 for a LIVELY music presentation at all-day-long listening levels. Jim Dowdy has listed the high mu octals.

In my experience, any octal is a degrade from half a 12AX7 Frihed89, because the octal socket requires eight soldered joints EXTRA, tube elements to octal pins. On a mu of 100 tube, THIS alone is an audible sonic degrade.

The 9 Pin miniature 12AX7 has the tube elements leading right out of the tube envelope, with NO extra soldered connections. A Loctal 7B4 is similar, but its sometimes hard to keep 7B4 tube pins from rusting.

Jeff Medwin

 

RE: What octals?, posted on December 6, 2014 at 07:06:22
Garg0yle
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Posts: 859
Joined: December 1, 2014
 Originally I planned on trying the 6SQ7 as a pseudo half 12AX7.
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RE: BB Proof 2A3 DC, posted on December 6, 2014 at 07:30:00
Mr_Steady
Audiophile

Posts: 2042
Location: North Florida
Joined: August 19, 2014
 " I have to decide if I need to put just one or two switches on it. The second switch could potentially be a provisional switch for a delayed start was my thinking."

I was wondering if a stand-by switch would solve any arching problem. Don't forget a nice retro looking analog meter with a top-side trim pot.

Please don't use the 5V4. I've never heard it sound good. I prefer the 5U4G in all amplifiers, more than any indirectly heated rectifier.

My little vote goes to 6P15P as driver tube. Probably not enough gain, but it would be so cool.

Jamie



Big speakers and little amps blew my mind!

 

RE: BB Proof 2A3 DC, posted on December 6, 2014 at 07:53:11
Garg0yle
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Posts: 859
Joined: December 1, 2014
 "I was wondering if a stand-by switch would solve any arching problem."

Hopefully

"Don't forget a nice retro looking analog meter with a top-side trim pot."

That would be neat. I may or may not have the room with the current chassis, although there is nothing stopping me from making a front panel similar to old Western Electric theater amps.
Also LEDs were previously suggest and would be another option.

"Please don't use the 5V4. I've never heard it sound good. I prefer the 5U4G in all amplifiers, more than any indirectly heated rectifier."

I am not married to it, I don't think I have any either, at the time the 5V4 was in my iteration of the Asano power supply.
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RE: BB Proof 2A3 DC, posted on December 6, 2014 at 08:20:29
Mr_Steady
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Posts: 2042
Location: North Florida
Joined: August 19, 2014
 "Also LEDs were previously suggest and would be another option."

Paul said no SS, but maybe down the road? TBDL. Really for a first build I'm sure you don't want to mess with a meter. You would just test the bias with your voltmeter.

Carry on,

Jamie






Big speakers and little amps blew my mind!

 

RE: BB Proof 2A3 DC, posted on December 6, 2014 at 08:30:48
RPMac
Audiophile

Posts: 377
Location: So. Mississippi
Joined: January 3, 2005
 PJ will have a negative opinion of a standby switch unless it is at rated voltage.

I'd like to see a 4P1L driver in a 'Monkey' layout, maybe with filament bias. Not much gain, but all DHT would be sweet! Worth the trade off?

 

RE: BB Proof 2A3 DC, posted on December 6, 2014 at 08:36:46
Garg0yle
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Posts: 859
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 You are correct.
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RE: BB Proof 2A3 DC, posted on December 6, 2014 at 08:38:22
Mr_Steady
Audiophile

Posts: 2042
Location: North Florida
Joined: August 19, 2014
 "PJ will have a negative opinion of a standby switch unless it is at rated voltage."

Then rate that voltage!

I hope 4P1L is in the pool too.

Jamie

Big speakers and little amps blew my mind!

 

RE: BB Proof 2A3 DC, posted on December 6, 2014 at 08:41:26
Garg0yle
Audiophile

Posts: 859
Joined: December 1, 2014
 "PJ will have a negative opinion of a standby switch unless it is at rated voltage."

I agree, I wasn't sure if there was some other way it could be used rather then switching high voltage.
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RE: BB Proof 2A3 DC, posted on December 6, 2014 at 08:59:47
Mr_Steady
Audiophile

Posts: 2042
Location: North Florida
Joined: August 19, 2014
 "Not much gain, but all DHT would be sweet! Worth the trade off?"

To me it would be worth the tradoff. I think people should get their gain on the front end of their system. Even if it means adding a 12ax7 gain/buffer stage to their CD player. Or using a preamp with gain instead of a TVC or passive pre.

Having said that the 4P1L is microphonic, and these great builders you see on line go to great lengths to mitigate that. Like using rubber suspension to isolate the tube from the chasis. I think the theme of this build is American BB proof, not European Finesse. I like European Finesse, don't get me wrong.

Jamie

Big speakers and little amps blew my mind!

 

Amperite octal time delay relay tube, posted on December 6, 2014 at 09:58:09
Jim Dowdy
Manufacturer

Posts: 1518
Location: Atlanta, GA
Joined: July 22, 2000
 Assuming you are operating with a nominal line voltage of 120 v, I recommend keeping the B+ transformer separate from filaments/bias, and install one of the Amperite TDRs on the primary of the B+ transformer.



 

I. Topology, posted on December 6, 2014 at 10:48:52
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001
 As I get things documented, I will post in this thread the circuit and some descriptions of the reasoning around the power supply, driver, and output stages. I'll revise those to incorporate things that come up, and eventually package it as a PDF file. One thing I've already added to the requirements is "Easily upgraded with better components". The purpose of describing my reasoning is to assist those who want to modify the design for their own purposes.

I. Topology

The chosen topology is a variant of the "monkey on a stick" which was quite popular on the internet in the nineties. The great advantage of this approach is that it always provides a negative DC bias to the power tube, even if the driver tube dies or is removed. This solves the sparking and cathode stripping issues, especially at startup.

I have chosen a power supply voltage of 450 volts, as a compromise between the high voltage requirements of direct-coupled designs, versus safety issues and the available voltage ratings of electrolytic capacitors. To get away with this voltage, the plate to cathode voltage of both driver and output tube must be relatively low. Therefor the 2A3 operates at the typical spec sheed value of 250 volts, 60mA, 2500 ohm load. The driver must have a low mu and low plate impedance; I have chosen the widely available 6J5GT.

Voltage budget:
output transformer DC drop 20v
2A3 plate to cathode 250v
2A3 bias 45v
driver plate to cathode 130v
driver bias 5v
Total 450v

 

RE: I. Topology, posted on December 6, 2014 at 12:21:11
Mr_Steady
Audiophile

Posts: 2042
Location: North Florida
Joined: August 19, 2014
 Thank you Paul,

Is this going to be a "full monkey" as described by Thorsten in 2010;

"In many ways the DRD and "Full Monkey" are the same, actually the DRD could be called a "halve monkey".

The name comes BTW from the old "Monkey on a stick" toy and a "full monkey" simply uses a single resistor chain to which all cathodes are returned, the key is to remove the need for the driver cathode bypass capacitor.

Hence any DC Coupled or DRD circuit can be fully monkeyed up..."



Big speakers and little amps blew my mind!

 

BB Proof Circuit, posted on December 6, 2014 at 12:52:43
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001



Here is the first draft circuit.

 

RE: I. Topology, posted on December 6, 2014 at 12:57:01
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001
 The circuit is up now.

It's not a full single-stick monkey; I prefer to have the DC feedback at the driver cathode to stabilize its operation against power voltage fluctuations. By running the driver low and hot, the cathode resistor is small enough (around 560 ohms) to be unbypassed without raising the effective plate impedance too much. Details will follow.

 

Q, posted on December 6, 2014 at 14:30:51
gluca
Audiophile

Posts: 1102
Location: SomeWhere Islands
Joined: February 17, 2005
 Paul

I tried this design with zeners and VR gas tubes to bias the upper tube (replacing the 3k/20W resistor and no bypass caps clearly) ... any experience with this variant?

g

 

RE: BB Proof 2A3 DC, posted on December 6, 2014 at 14:46:16
Al Noakes
 I played with filament bias quite a lot and now just find it wasteful in terms of heat with better sounding alternatives on most situations . Filament bias can be detrimental as it puts any noise on the filament supply directly in series with the signal . I find the best way of using the 4P1L is with series filaments running CCS fed DC , taking the cathode connection from the filament centre-tap and running LEDs or schottky diodes for bias . In a 'monkey' amp you can place the cathode circuit of the driver stage in series with the cathode resistor of the output stage , then the cathode bypass cap can be removed . Works in a similar fashion to filament bias as it runs output stage current through the driver cathode bias resistor meaning a much lower value can be used . This has the added benefit of self-regulation

Al

 

RE: Q, posted on December 6, 2014 at 15:23:50
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001
 The problem with that is, the direct coupled design is excessively sensitive to power-line voltage variations. Not an unsurmountable problem of course! but I'm trying to keep this one simple.

 

II. Power Supply, posted on December 6, 2014 at 15:26:05
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001
 Notice I have already slightly altered the circuit; I'll post a revision after all the words are up and we see some feedback.

Power Supply

Direct coupled amplifiers need very high voltages because there is no coupling capacitor between stages. The highest voltage rating for widely available electrolytic capacitors is 450v; components that can produce and tolerate higher voltages are harder to find, so that is the voltage chosen. The fairly typical Hammond 273X power transformer is rated 350-0-350 volts at 110mADC, 5v at 2A, and 6.3v at 4A. It is also available with universal primary and 50Hz rating as the 373X. With a 5V4 rectifier, about 440 volts should be available. To keep the voltage loss low, a CLC filter is used; Hammond 156L is 5H at 135 ohms. Ripple should be small enough to produce less than 1mVrms hum, giving capacitors of about 50uF.

The first capacitor seems large, but at 60mA total current, the peak rectifier plate current is well within the maximum rating. A 47uF 450v rating would work in place of the two 100uF in series, but I've shown the more robust method. A film or motor run at 600v would be nice. The second capacitor is split, as a cathode bypass plus ultrapath capacitor; this is to keep the signal current loop short. The ultrapath capacitor is the first candidate for upgrading. A 5AR4 can substitute for the 5V4 easily; other rectifiers may need different filament current and supply voltages to get the right output voltage.

A separate 2.5v transformer such as the Hammond 166M2 is used for the 2A3 filament; Hammond does not offer a 2.5v transformer with 50Hz rating. There are a wide variety of other ways to power a 2A3 filament, however!

 

RE: II. Power Supply, posted on December 6, 2014 at 17:05:10
Garg0yle
Audiophile

Posts: 859
Joined: December 1, 2014
 Awesome, I am going to play around with PSUD and see what I can do with my iron.

I also should pick out a spot for the plate choke(s) to go underneath my chassis.

The dimensions of the Hammond 156C appear to be "1.5 in W x 2.81 in L x 1.69 in H" which should fit OK.

Cheers.
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RE: II. Power Supply, posted on December 6, 2014 at 17:55:37
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001
 Make sure that choke is well spaced from the power transformer and filter choke, and as much as possible with its axis perpendicular to the power transformer axis. It's more sensitive than the output transformer, which should also be well spaced and oriented.

What I have often done is to mount the power transformer on some plywood and connect its primary to a line cord. Then put a voltmeter on the choke or OPT primary and move them around, reading the voltage picked up and looking for nulls.

 

RE: II. Power Supply, posted on December 6, 2014 at 18:04:02
Garg0yle
Audiophile

Posts: 859
Joined: December 1, 2014



OK so with a little tinkering using my 370V taps, a 5AR4 and a 7.5H 220Ohm choke I can get a solid 449.7 volts.

Ripple is 29.5 mV.

It's got a little jiggle while ramping up, I've never had that before in PSUD.

I am going to post a screen shot here, see if I am missing anything.

Thanks.
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Thanks and..., posted on December 6, 2014 at 19:31:55
SteveBrown
Audiophile

Posts: 2454
Location: Portland, OR
Joined: November 14, 2002
 Paul, thanks for doing this! You mentioned some issues regarding choke and transformer placement. Even the best circuit in the world can be ruined by poor chassis layout. It will be interesting to see what people come up with to achieve lowest hum.

 

RE: II. Power Supply, posted on December 6, 2014 at 20:09:22
Garg0yle
Audiophile

Posts: 859
Joined: December 1, 2014
 On the topside of my chassis I have the PT-choke-OPT all in a row along the back. The chassis is kinda small in an attempt to keep it rigid.
The choke and OPT are potted, so hopefully they will be OK.

The 156C can go underneath toward the front in a corner close to the 6J5 and/or 2A3.
I will try your suggestion to use the DMM to see if I can find a sweet spot for the 156C. I do have to order these first though.


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RE: II. Power Supply, posted on December 6, 2014 at 23:13:24
SteveBrown
Audiophile

Posts: 2454
Location: Portland, OR
Joined: November 14, 2002
 Hey Garg0yle, years ago a company called Welborne Labs came out with a DRD style amp (similar to the Monkey). You can find chassis layout photos on line if you poke around. They had both a solid state and tube rectified version of it. IIRC it could be ordered for a 45, a 2A3 or a 300B. It was reported to be very quiet.

 

RE: BB Proof Circuit, posted on December 7, 2014 at 03:22:56
vinnie2
Audiophile

Posts: 4481
Location: North Carolina
Joined: September 28, 2013
 It's nice to see the 125ese getting used in a design by an acknowledged first rate designer. I think it is really one of the best bargains out there for SE opts at this time.
Nice work Paul, I may have to bread board it myself. Thanks for offering it here on the forum!

 

RE: II. Power Supply, posted on December 7, 2014 at 04:21:14
jiv
Audiophile

Posts: 23
Joined: December 3, 2005
 How about Hammond 266M2? It's 50/60 Hz.

 

RE: II. Power Supply, posted on December 7, 2014 at 06:43:51
DIY John
Audiophile

Posts: 441
Joined: November 29, 2001
 Is the indirectly heated rectifier really needed for the BB-proof aspect (slow start to B+) or would a directly heated rectifier be acceptable, assuming a higher transformer voltage to compensate?

 

RE: II. Power Supply, posted on December 7, 2014 at 07:51:39
Garg0yle
Audiophile

Posts: 859
Joined: December 1, 2014
 Thanks.
OK so I had a look at a few of the Welborne DRD via google image search.

My layout is similar, the differences being:
-I have my choke jammed in between the PT and OPT on the topside.
-The 2A3 is in between the input tube and rectifier, placing the 6J5 on the opposite end of the power supply area. (Although I see some variations, both 2 and 3 tube versions of the Welborne DRD)
-The plugs and terminals are going to be along the "long" side of the chassis. The long sides on mine will be the front and back. I pondered turning them 90 degrees like the Welborne, but I will leave that for now as I don't see an apparent advantage to do so at this point.
Although I might put the power switch near the IEC socket like the Welborne has. I haven't had a problem with front mounted power switches in the past, however I think it might be prudent on this one.

I don't know what the orientation is of my OPT and choke though, since they are enclosed. I will orient these by their lead-outs at the bottom to minimize crossed wires etc.

I noted the plate choke on the DRD appears to be on the "front" wall near the tube sockets, similar to where I will place mine.

Given the size of my chassis the layout is fairly decent, time will tell.
If it doesn't work out I would have to go to a bigger chassis as opposed to rearranging the 12"x8"x2" chassis I have now.


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Cool!, posted on December 7, 2014 at 09:10:48
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001
 Thanks - I missed it because it's not in my old paper catalog. Thanks!

 

RE: II. Power Supply, posted on December 7, 2014 at 09:23:05
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001
 The "monkey" configuration protects the 2A3 from the main violence of a rapid start. There is still some current drawn as the filament heats, of course.

 

Power Supply Cap, posted on December 7, 2014 at 14:43:52
Mr_Steady
Audiophile

Posts: 2042
Location: North Florida
Joined: August 19, 2014
 I found an ASC 50uf 515vdc PIO cap and Angela instruments.

Is 50uf close enough for C1?

Does ASC mean it's a Start cap?

I also found a Sangamo PIO cap that is rated 47uf and 600v, but it is listed as a start cap.

Any advice?

Jamie

Big speakers and little amps blew my mind!

 

RE: Power Supply Cap, posted on December 7, 2014 at 15:00:26
Garg0yle
Audiophile

Posts: 859
Joined: December 1, 2014
 ASC is the manufacturer and they do appear to be motor "run" caps at Angelas, at least if they are the same as these: http://www.ascapacitor.com/traditional_film.php

50uF should be fine for C1.

I would pass on the Sangamo unless you can be certain you have a model that is suitable.
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RE: Power Supply Cap, posted on December 7, 2014 at 15:07:36
Mr_Steady
Audiophile

Posts: 2042
Location: North Florida
Joined: August 19, 2014
 Thanks Garg0yle,

I had just googled ASC. I'll do better next time.

Do you think 515v would allow going up to a 5U4G?

Another poster mentioned C2 as important. Is that the 100uf 250v cap?

Do you think the 100uf 350v Ultrapath cap is worth a nice cap?

I like the layout of Paul's schematic. It's the first one I ever seen done like that.

Jamie

Big speakers and little amps blew my mind!

 

RE: Power Supply Cap, posted on December 7, 2014 at 15:11:50
Mr_Steady
Audiophile

Posts: 2042
Location: North Florida
Joined: August 19, 2014
 Sangamo 772501

50uf, 720vac


Big speakers and little amps blew my mind!

 

Another source for motor runs, posted on December 7, 2014 at 15:55:30
RayP
Audiophile

Posts: 727
Location: Maryland
Joined: June 30, 2005
 I have a bunch of 45 / 7 400 vac round motor run caps from this store. My understanding is that the DC rating is at least 1.4 times the 400 VAC rating. The store doesn't have them now but there are other caps with similar ratings.

I have had great success using Goop to attach these to steel / aluminium or polycarbonate. The bond is strong enough to hold them but not quite so strong that you can't remove them.

Maybe I will build design this since I have never done a 2A3 amp before.

ray

 

RE: Power Supply Cap, posted on December 7, 2014 at 16:04:18
Garg0yle
Audiophile

Posts: 859
Joined: December 1, 2014
 I should clarify by being suitable, it is known as a "motor run" capacitor as opposed to a "start" Capacitor.
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RE: II. Power Supply, posted on December 7, 2014 at 16:07:11
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005
 The Classic Hammond 200 Series power transformers now are made with 115 VAC AND 125 VAC taps on the primary. If your home's line voltage is a typical 122 VAC, and you use the 115 VAC primary winding, you get a 1.0608 step up ratio. This makes the 350-0-360 VAC winding a 373.1 VAC winding, nominal.

Also, you used 165 Ohms as the PSUD PT DCR. That, without looking, is likely the end to end ( 350 - 350 VAC ) total winding. On such a center tapped transformer, you only use EITHER end to center tap as the DCR.

But wait, it gets better, you can be more precise, and we should be. You can measure the DCR of the primary, and the step up ratio of the primary winding, to the High Voltage secondary winding, to determine the "best " DCR numbers to input into PSUD 2.

I will look for that Formula and post it herein.

----------------------------------

Hi Jeff!

When you work with Duncan amps PSU Designer II, please use the formula for Rtransformer:

Rtr. = Rsec. + (n x n x Rprim.)

Rsec. = DC Resistance secondary [Ohm], measured between (0V - high volt) of one 'leg'.

n = step-up ratio (= voltage secundary / voltage primary)

Rprim. = DC Resistance primary [Ohm]

This is the transformer resistance as it's 'seen' by the rectifier
tube.


Jeff Medwin

 

RE: Power Supply Cap, posted on December 7, 2014 at 16:09:07
Garg0yle
Audiophile

Posts: 859
Joined: December 1, 2014
 I think, someone correct me on this if I am mistaken, that those two 100uF capacitors are actually seen as one 50uF capacitor with double the voltage rating of the lowest rated capacitor, in this case the lower rated cap is 250v, effectively making it a 500V rated cap to be a little higher then the 450V B+

Someone else will have to comment on whether these should be oil capacitors or not.

I myself am running out of room!
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RE: II. Power Supply, posted on December 7, 2014 at 16:14:30
Garg0yle
Audiophile

Posts: 859
Joined: December 1, 2014
 "Also, you used 165 Ohms as the PSUD PT DCR. That, without looking, is likely the end to end ( 350 - 350 VAC ) total winding. On such a center tapped transformer, you only use EITHER end to center tap as the DCR."

I thought you would be shocked by that.
They are in fact 330Ohms from end to end.


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RE: Power Supply Cap, posted on December 7, 2014 at 16:16:22
Mr_Steady
Audiophile

Posts: 2042
Location: North Florida
Joined: August 19, 2014
 47uf 600v Sonicaps were at parts connexion for $15.


Big speakers and little amps blew my mind!

 

RE: Power Supply Cap, posted on December 7, 2014 at 16:22:01
Mr_Steady
Audiophile

Posts: 2042
Location: North Florida
Joined: August 19, 2014
 "I myself am running out of room!"

Don't laugh, and I'll probably get flamed.

I've been collecting cigar boxes for a while as possible enclosures. I think I will do two for each monoblock. A power supply box, and the main box, connected by an umbilical cord. I think I will hard wire the umbilical.

Just playing,

Jamie

Big speakers and little amps blew my mind!

 

RE: Another source for motor runs, posted on December 7, 2014 at 16:26:13
Garg0yle
Audiophile

Posts: 859
Joined: December 1, 2014
 The more the merrier.

Do you think those are fairly recent stock?

I will bookmark this site, although I didn't notice any run caps with a high enough voltage rating.

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RE: Another source for motor runs, posted on December 7, 2014 at 16:40:38
Mr_Steady
Audiophile

Posts: 2042
Location: North Florida
Joined: August 19, 2014
 Hey Ray,

I knew there was a conversion. I learned a lot of this years ago, and then backed off DIY.

Thanks for the link.

Here is a film in oil cap, Obbligato, from DIY hi fi supply. 47uf and 630v. That may give me wiggle room for a 5u4g?

Jamie

Big speakers and little amps blew my mind!

 

free monkey on a stick for lunch., posted on December 7, 2014 at 16:40:40
dave slagle
Manufacturer

Posts: 5430
Location: NYC
Joined: April 27, 2001
 It is probably worth reading Jeremy's take at the link below.


dave

 

III. Output Stage, posted on December 7, 2014 at 16:47:20
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001
 Output Stage

I have chosen to operate the 2A3 at its maximum rated dissipation of 15 watts. To operate it at lower dissipation, plug in a 5Y3 rectifier to reduce the voltage! The indicated Hammond 125ESE is a popular and inexpensive output transformer; its inductance of around 10 henries is marginal but works well enough for most audiophiles. There are many superior output transformers of 2500-3000 ohms impedance which can be substituted with no other circuit changes.

I've shown a 220 ohm grid stopper. The value is flexible, 47 to 10,000 ohms having been used by others – but don't leave it out, the 2A3 has pretty high transconductance and oscillates easily. Carbon composition is the gold standard for grid stoppers, but there is some evidence that metal or carbon film are acceptable and may be more robust, stable, and easier to find.

I chose a 25 ohm hum pot partly because Radio Shack has had a decent wirewould rheostat of that value for decades. This should be wirewound or other bulk metal because of the high currents flowing through it; other materials are prone to be noisy. You can dispense with it by using the 2.5v transformer's center tap, but in my experience that will produce too much hum unless you have an exceptional 2A3.

The cathode resistors are shown with what I think is the minimum power rating for reliable operation. They will get hot! Note that the popular 25-watt resistors in finned aluminum housings are meant to be bolted to a heat sink of 25 square inches – that's a LOT of chassis area and it will get pretty hot. I prefer the old-fashioned ceramic core wirewound with some air circulation to cool it.

The cathode bypass and ultrapath caps have been discussed with the power supply.

The optional meter shown should be set for a zero indication, so the voltages are the correct fraction of the total. This gives pretty accurate operating points over a wide range of actual power supply voltages. A zero-center meter of +/-1mA sensitivity will cover an error of roughly +/-100v. You can just use a regular voltmeter for periodic trimming. Be aware there are high voltages on both terminals; I don't recommend bringing these connections outside the amp!

 

IV. Driver Stage, posted on December 7, 2014 at 16:49:41
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001
 Driver Stage

The driver stage has the most constraints placed on it. It must have a low enough source impedance and high enough current capability to drive the Miller capacitance of the 2A3 plus the plate choke self-capacitance; these alone limit the plate resistance to about 20Kohms. Being choke-loaded, the choke inductance must be high enough relative to the plate resistance to retain satisfactory bass extension as well. At 20K plate resistance, a -3dB point of 20Hz requires 159 henries. High-inductance plate chokes are few and far between, but Hammond does make one rated 150 henries at 8mA. And finally, the grid bias must be high enough to avoid driver grid current on signal peaks. The late John "Buddha" Camille recommended a bias of -2v plus the peak input signal (2.25v for this design, total 4.25v). In my own experiments I have not seen a grid current when the bias is at least 0.8v, so I believe 3.05v is safe. The design has about 3.4v bias. Any higher gain in the driver would produce a lower bias voltage, so we are limited to around a mu of 20.

The nominal pate resistance of the 6J5 is 8K ohms, so there is some margin. I elected to use this margin to obtain cathode bias without bypassing the resistor. Since this is a direct coupled amplifier, whose main purpose is to get rid of an audible coupling capacitor, that seems worthwhile. If we run the tube at high current, we can use a small cathode resistance to get the bias, and it will not add too much equivalent plate resistance. In this case, a resistance of 560 ohms gives 6mA current and adds about 11K ohms for a total of 19K ohms equivalent plate resistance. As a side benefit, the tube is very linear at this condition.

The remaining driver parameter is headroom – the plate voltage swing from zero bias to the quiescent point should exceed the required drive voltage. I have here chosen a 50% margin (70v swing vs. 45v required) as a compromise between linearity and keeping the total voltage low.

The actual voltages are adjusted by making the cathode resistance a potentiometer which can be trimmed as needed. This allows for drift of tube parameters with aging and power supply voltage variations. This pot should be wirewound or other bulk metal to ensure quietness, much like the hum pot on the 2A3.

Within the above constraints, it is possible to use other tubes – types 26, 27, 37, 56, 76, 6N7, 6N1P, 955, and 5670 come to mind. I do not offer detailed designs for any of these.

Notice that the driver plate current will drop some DC voltage across the plate choke, in this case 22 volts. That is subtracted from the 2A3 bias of 45 volts to obtain 23v drop across the upper 2A3 cathode resistor. 23v at 60mA (2A3 plate current) is 383 ohms; I chose 390 as very close. The lower resistor drops the remaining voltage, but carries less current (60mA – 6mA = 54mA) – calculate 2907 ohms, specified 3000 ohms. These calculations will have to be re-done if any different tube is used.

 

RE: Power Supply Cap, posted on December 7, 2014 at 16:57:55
Garg0yle
Audiophile

Posts: 859
Joined: December 1, 2014
 Parts Connection does have a nice selection.

I think cigar boxes would look very nice, although I'm not crazy about the all wooden box thing, it is something I have contemplated many times.

Ideally they would have a metal lining with the wood box around it, which is a little tougher in your case as you already have the finished boxes.
It's doable, just more a little more work, but hey that's part of the fun.

You might be able to get some of those Hammond chassis to fit from Parts Connection, as long as it works for the layout, IMO it wouldn't matter if the wooden box was a little bigger.
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Wow - thanks!, posted on December 7, 2014 at 16:58:37
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001
 "The Classic Hammond 200 Series power transformers now are made with 115 VAC AND 125 VAC taps on the primary"

I didn't know that. As with the filament transformer, I am out of date with my Hammond catalog - this is really good to know. Should solve a lot of "my transformer buzzes" posts!

 

RE: Power Supply Cap, posted on December 7, 2014 at 17:06:55
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001
 In the revised circuit (I'll post it after a few more comments, with a new version number) I've suggested using four 100uF/350v caps, with C1 being two of them in series. Electrolytics really are happier with no more than 80% of their rated voltage on them.

Something similar is the case for film caps. I recommend digging up the manufacturer's literature and reading it; CDE is a really good starting point.

 

RE: Power Supply Cap, posted on December 7, 2014 at 17:11:44
Mr_Steady
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Posts: 2042
Location: North Florida
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 Thanks Paul.


Big speakers and little amps blew my mind!

 

RE: free monkey on a stick for lunch., posted on December 7, 2014 at 17:15:36
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001
 Thanks Dave - that takes me back! Very similar design.

 

RE: Power Supply Cap, posted on December 7, 2014 at 17:36:20
Mr_Steady
Audiophile

Posts: 2042
Location: North Florida
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 Yes, I thought about lining the boxes. I think diyhfsply has copper shielding. BH doesn't line their wood boxes, but I think they shield the signal wire instead.

After reading Paul's explanations, I decided to build it stock with the 5v4s, no modifications.

I think the Hammond OPTs might work well for me, because I would only use this amp in a very limited bandwidth, like 300hz to 1,800hz.

I want to give this a crack, but I'll go slow.

Jamie

Big speakers and little amps blew my mind!

 

RE: Power Supply Cap, posted on December 7, 2014 at 17:49:02
Garg0yle
Audiophile

Posts: 859
Joined: December 1, 2014
 "BH doesn't line their wood boxes, but I think they shield the signal wire instead."

Those amps do have a metal top plate to hold the parts together, maybe you could fit something like that to the underside of your cigar boxes, then use the shielding tape if necessary.
That way you won't have a problem if the cigar box splits it's lid etc.

Anyhow I'm just making suggestions, I'm sure you know what you are doing.
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RE: Power Supply Cap, posted on December 7, 2014 at 18:00:17
Mr_Steady
Audiophile

Posts: 2042
Location: North Florida
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 "Anyhow I'm just making suggestions, I'm sure you know what you are doing."

Not so much.

One step up from a bread board is what I'm looking for. I figure using two boxes (PS-main amp) will split the weight load. Maybe even mount the OPT inside the box.


Big speakers and little amps blew my mind!

 

449.27 VDC and 66.84 mVAC with 122 Line on 115 Tap, posted on December 7, 2014 at 19:30:00
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005



Hiah Paul,

Have I inputted this PSUD2 simulation correctly? If so, will the Driver stage be happy with 66.84 mVAC of B+ ripple? Am I looking at it wrong, simulating it wrong, or what... both ?? Oh yes, the driver stage B+ ripple will perhaps be divided in mVAC by those two high value dividing resistors, which I was unable to display in PSUD.

I usually try for 2 mVAC of ripple, or less, to the driver. Anything under 850 mVAC is fine to the non-fussy 2A3 Finals.

I keep looking at this, and decided to ask for your help.

Can you, or anyone simulate what the ripple will be at "idle" at the top of the choke load, the B+ that feeds the input / driver stage please??

Is higher driver stage ripple a "topology trade-off" on any "Monkey On A Stick" design, and / or the 1947 Jack Robin-Chester Lipman L-W amp, where the B+ to the 6SF5 is also derived from the Final's tube cathode, with minimal power supply decoupling ??

Jeff Medwin

 

RE: 449.27 VDC and 66.84 mVAC with 122 Line on 115 Tap, posted on December 7, 2014 at 20:20:58
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001
 In my quick try I used a higher winding resistance and got more like 50mV peak to peak; otherwise my simulation was pretty much the same.

The driver is fed from its plate choke, whose impedance at 120Hz is 113K ohms - that gives a lot of reduction. The ripple at the choke takeoff is half that of the full PSU, from capacitive splitting - more help. Not having built this, or simulated it, I can't be sure. But another cap at the high voltage end of the plate choke will kill the driver hum, if it's a problem.

I didn't show the calculation, but here it is: 1mVrms at the speaker is 2.8mV peak to peak, which at the primary is 50mV peak to peak. The filament will make about 2mVRMS at the 8-ohm tap, so this seems like a reasonable spec. Got to leave some room for the reality check once it's running! :^)

 

Even better ..., posted on December 7, 2014 at 21:56:08
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001
 If you download the specs for the one particular transformer, you get the open circuit voltage and the winding resistances, as well as showing the two primary taps. 273X is 381v, 85 ohms; 125v primary is 2.889 ohms. I'm seeing 461v with 48mV pk-pk ripple on PSUD-II, assuming 125v in on the 125v winding.

The current specs are now in rms current, so you can use PSUD and see the increased current available with a choke-input filter compared to cap-in. Very nice!

Hammond is really being responsive to DIY needs. My power line is 123.7vAC right now (10PM local time).

 

How about, posted on December 8, 2014 at 00:53:36
Frihed89
Audiophile

Posts: 15703
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 Any of the 025 models from MagnaQuest? The DS-025 is the basic model.

 

Operating and shelf life for motor runs, posted on December 8, 2014 at 01:17:16
RayP
Audiophile

Posts: 727
Location: Maryland
Joined: June 30, 2005
 The link to a PDF on the Digikey site states:

RELIABILITY AND LIFETIME
AC capacitors are rated for a full service life of 60,000 h with an
estimated 94% survival rate when operated at full rated voltage,
60 Hz and rated ambient temperature.

SHELF LIFE
AC capacitors are expected to perform for their full service life
objective after being exposed to a maximum shelf life of 10+
years when stored in a controlled environment.

ray

 

two 156C in series, posted on December 8, 2014 at 06:10:24
RayP
Audiophile

Posts: 727
Location: Maryland
Joined: June 30, 2005
 Hi Paul,

I was reading the following from Gary P about using two of the inductors in series. See post #5 in the link.

The 22v drop of the second inductor could account for almost the whole drop of the 23v across the 390 ohm resistor. Perhaps the 390 resistor could be replaced by a 16 or 17 ohm resistor to measure the current.

ray

 

No but......, posted on December 8, 2014 at 07:42:40
bouncy ball
Audiophile

Posts: 1221
Location: British Columbia
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 you need to find a way to make sure the HV ramp up very slow and not overshoot in first couple seconds.
I use 5r4 but with a delay timer on HV, separate filament transformers for driver and output tubes plus tube voltage regulation like those vintage Tektronix power supply.

 

RE: two 156C in series, posted on December 8, 2014 at 11:32:53
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001
 In the startup interval, as the 2A3 is heating but the 6J5 is still cold, the 390 ohm resistor provides a negative bias to the 2A3, limiting its current as well as the voltage across the cathode bypass capacitor.

Treading close to the spitball-proof amp? :^)

 

RE: How about, posted on December 8, 2014 at 11:37:17
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001
 Mike is a friend, and also has had a long relationship with Bottlehead, so I can't comment beyond saying I like them.

 

Thanks for mentioning that!, posted on December 8, 2014 at 14:36:35
caffeinator
Audiophile

Posts: 1729
Location: Pacific Northwest
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 I actually picked up a couple of those chassis from Welborne on a clearance one time...always wondered how to figure out the placement of the items 'under the hood'...think I might add a "BB proof half monkey ala DRD chassoise" to my hot stove on deck circle...

 

RE: Thanks for mentioning that!, posted on December 8, 2014 at 22:18:55
SteveBrown
Audiophile

Posts: 2454
Location: Portland, OR
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 If you go to their website (still in business I guess) you can buy a PDF of the construction manual. I did it weekend but it didn't open, but a day later they sent me an email copy. Anyway, clearly Paul's circuit is different / better, but this is a great guild to the layout.

 

RE: III. Output Stage, posted on December 9, 2014 at 04:15:39
SteveBrown
Audiophile

Posts: 2454
Location: Portland, OR
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 Paul, on the two electrolytic 100uf caps in series, thoughts on reducing those to around 50uf to allow easier use of Solen film caps?

 

RE: two 156C in series, posted on December 9, 2014 at 05:27:18
RayP
Audiophile

Posts: 727
Location: Maryland
Joined: June 30, 2005
 It took me a while but finally I can see why the cold 6J5 would be a problem.

For educational purposes, if I used the dual switch arrangement that turns on the heaters first, would the second inductor have been a good idea?

I realize that the dual switch would not be in the BB spirit of the amplifier design but I've used it a lot in the past.

ray

 

RE: two 156C in series, posted on December 9, 2014 at 11:28:58
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001
 That would resolve this particular problem as long as the 6J5 is functioning. As an engineer I am always looking for ways to fail safe, such as when the 6J5 dies or is accidentally removed from the amp.

I'll just mention that there are commercially available plate chokes with more inductance and less DC resistance, which would be a better approach IMHO. But, you know, if you build something yourself, you get to make the decisions!

 

RE: III. Output Stage, posted on December 9, 2014 at 11:33:27
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001
 The hum/ripple performance of the power supply is marginal. To do this you would want to improve that, such as adding an LC stage or using a filter choke of greater inductance. This would reduce the available voltage, unless either a different power transformer were used, or you switched to solid-state rectifiers.

 

RE: Thanks for mentioning that!, posted on December 9, 2014 at 11:45:05
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001
 re: "...clearly Paul's circuit is different / better", mine is nearly identical in conception - I bypass the 2A3 cathode resistor instead of the driver cathode resistor; that's about it. The topology is so simple, there are few variants possible.

Mostly what I have tried to offer here is some specific parts values as a help in getting started, and a description of how they were chosen for those who want to make modifications. Plus of course I could not have put someone else's commercial design in the public domain!

 

RE: BB Proof 2A3 DC, posted on December 9, 2014 at 20:26:19
Garg0yle
Audiophile

Posts: 859
Joined: December 1, 2014
 I think I am pretty much set on a layout, I need to make a decision on capacitor type since they vary so much in physical shape. I would like something similar to a axial leaded Sprague atom electrolytic.

That and I should decide to put the trim pots behind or beside the tube sockets, also I assume I should keep them internal to prevent accidental tampering. I remember these nice trim pots that were on an old Scott amplifier my Dad had, they were basically flush mounted and had to be turned with a flat head screwdriver. It would be nice to find some.

I did have a quick question:
How critical is it to have the 2.5VAC filiment lines isolated from other sources of AC?
I have a spot where I could either cross the high voltage secondaries (At roughly 90 degrees) of the power transformer, or I can route them in the vicinity of the lower voltage AC heater lines.


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There's only so many ways to turn a cat into a Monkey, posted on December 10, 2014 at 01:03:03
Frihed89
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Posts: 15703
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The schematic is for the cat. I believe it is the basis for at least 2 commercially available DC 2A3 amps I guess you could pot in place of R-2. With a few minor modifications this circuit could be made to play either a 45 or a 2A3.

The schematic comes from Robin & Lipman 1947 Practical Amplifier Diagrams. See the URL.

 

RE: There's only so many ways to turn a cat into a Monkey, posted on December 10, 2014 at 02:07:30
jiv
Audiophile

Posts: 23
Joined: December 3, 2005
 The same schematic (omitting R3 and R6) is also used in a Glass Audio article "Hybrid Tube Radio by David Wang" mentioned for example in Ejam's post.

http://www.audioasylum.com/cgi/vt.mpl?f=tubediy&m=25401

I just wonder, what are the 2A3 and 6SF5 voltages in that "Hybrid Tube Radio"?

 

RE: There's only so many ways to turn a cat into a Monkey, posted on December 10, 2014 at 10:34:32
Frihed89
Audiophile

Posts: 15703
Location: Copenhagen
Joined: March 21, 2005
 For the 2A3, plate voltage is around 275V and 40mA, or a bit lower. I don't know about the driver.

 

RE: IV. Driver Stage, posted on December 10, 2014 at 16:51:07
Mr_Steady
Audiophile

Posts: 2042
Location: North Florida
Joined: August 19, 2014
 PJ,

I looked at some better quality plate chokes, and I realized that the BH C4S would be cheaper. Are those kits supplied with any tables or equations, so they could be adapted to this amplifier?

I hope this question doesn't make you uncomfortable. I don't mean it to.

Jamie

Big speakers and little amps blew my mind!

 

RE: IV. Driver Stage, posted on December 10, 2014 at 17:19:11
Mr_Steady
Audiophile

Posts: 2042
Location: North Florida
Joined: August 19, 2014
 Belay that.

I just read the manual for a diy ccs board. The Hammond choke will do fine.


Big speakers and little amps blew my mind!

 

RE: III. Output Stage, posted on December 10, 2014 at 18:55:45
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005
 Steve,

Solen Film Caps are pretty dreadful audio performers, and only seem to be used because they are inexpensive versus others.

I suggest you look at the new breed of film caps, called DC LINK, applying the latest film cap technology, with a wide choice in voltages ( 600, 800, 1200 VDCs ) and uFs. Look up papers on them, compare specs. The ones we have audio tested are made by WIMA, available here in the USA, and there is also another line, made by VISHAY, and maybe one or two other Manufacturers.

Say " Goodnight Gracie "...... Say " Goodnight Blackgate WKZ ".

Jeff Medwin

 

PS caps, posted on December 10, 2014 at 21:53:47
Sidewinder
Audiophile

Posts: 254
Joined: April 13, 2001



Hello Drlowmu,

First a word to the Hall Monitors: Please forgive me if I am breaking protocol. I just need to post here and now.

I am following the generous thoughts of Paul Joppa on building his version of a DC 2A3 amp which I plan on building. Thanks a million Mr. Joppa.
I am now using a Uchida 2A3 clone amp the Bowei 2A3. I was going to upgrade the PS caps with solen 47uf 630v cap, but then I saw your suggestion of DC Link caps for ps filtering. Are these the ones?: http://www.mouser.com/ProductDetail/Vishay/MKP1848S65050JY5F/?qs=sGAEpiMZZMv1cc3ydrPrF2iz%2f2bi%2fpr6ughQJim8hsQ%3d

So far I've changed the coupling caps to Russian PIOs and I'm using JJ2A3s and GE6SN7s. I'd like to improve this amp some more without tearing it apart, so if you have any suggestions on improving this amp I'd appreciate it.
Regards,
David
PS. I'm still drinking Steve Bauer's veggie juice and I feel no pain in my joints. Thanks for that again. Do you have a recipe for just plain old muscle pain?


 

RE: IV. Driver Stage, posted on December 10, 2014 at 22:03:30
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001
 Only the choke has a low DC resistance, preventing the driver plate from exceeding the voltage at the choke positive attachment.

CCS does have sonic advantages but they bring out all the problems mentioned in the earlier thread.

 

Solens - was RE: III. Output Stage, posted on December 10, 2014 at 22:10:27
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001
 There is some listening experience to suggest that Solens take a long time to break in, but sound pretty good once that is done. Like 200-300 hours? There is not yet enough data to say anything definitively, just an interesting observation at this point. At least it's actual listening, no theory at all!

 

RE: BB Proof 2A3 DC, posted on December 11, 2014 at 09:16:10
Garg0yle
Audiophile

Posts: 859
Joined: December 1, 2014
 OK I think I am ready to apply a finish to the chassis(s).

I had more work to do then I thought.
A trip to theSource (Radio Shack was actually fruitful, as they had a couple of fuse holders I needed. I also picked up some binding posts, the first set were extremely cheesy, but they also had some spring load ones. I went with those.

Also I'm tired of filing out pretty holes for IEC sockets, so this time around I am going to use a M12 strain-relief pigtail. 7/16" round hole and it's done.

These decisions were made for expediency.

I still need some RCA jacks, but they are fairly common with a 1/2" hole, so I drilled for that size. (debated not even using a RCA socket, just a wire, but then I still need to grommet it and keep it secure so I wasn't really gaining anything in the effort department.)

Then I went to Home Depot to get a couple of suitable handles for the sides.

Eventually some small holes will need to be drilled for the choke and terminal strips, but the major machining is done. Hopefully I will be soldering some wire by the weekend.

Cheers.
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Circuit rev 2.2, posted on December 11, 2014 at 09:30:01
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001



In response to various ideas that have come up , I've revised the circuit slightly:

* The first power supply capacitor is now shown as two 100uF/350v caps in series, to provide a better voltage margin for long capacitor life.

* The lower 2A3 cathode bypass cap is raised from 250v to 350v so all the caps are the same.

* I have added a capacitor (also the same) from the tap on the 2A3 cathode resistor to ground; this reduces hum to the driver stage. Thanks to drlowmu for bringing this possible issue to my attention!

With these changes a pair needs ten identical capacitors, which is a common price break point.

I'll revise further if there are issues with the amp once a few have been built.

 

RE: PS caps, posted on December 11, 2014 at 16:01:48
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005
 Go with the WIMA DC Links, not VISHAYS.

Readily available.

Jeff Medwin

 

RE: PS caps, posted on December 11, 2014 at 17:33:21
Mr_Steady
Audiophile

Posts: 2042
Location: North Florida
Joined: August 19, 2014
 Hi Jeff,

You've been giving us some good advice. I appreciate it. How many men can get PJ to amend his circuit?

I found at Mouser:

WIMA

50uf 600v $25
50uf 800v $25
100uf 600v $43
100uf 800v $45

You get ten 100uf 600v for $395. Call it $400.

$43 is a boutique cap price. Clarity Cap same value, and maybe $7 bucks more, or maybe the CC isn't such a boutique price after all.

I've liked WIMAs for a long time, but I've only heard them as coupling caps. I always thought they would excell in the PS. They are perfectly good coupling caps, and what more can you say? I have a bag of .22uf 600v ones.

Would you use them in C1 position instead of a good PIO or Film in Oil? I think I would like to use the wima in the ultrapath position.

Jamie


Big speakers and little amps blew my mind!

 

RE: PS caps, posted on December 11, 2014 at 18:07:17
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001
 Panasonics run about $15 for DC link.

No audio experience here, just a Scots connection ...

 

RE: PS caps, posted on December 11, 2014 at 18:32:54
Mr_Steady
Audiophile

Posts: 2042
Location: North Florida
Joined: August 19, 2014
 My last name is Scottish, and I save my money.

Thanks for the great tip PJ!




Big speakers and little amps blew my mind!

 

RE: PS caps, posted on December 11, 2014 at 18:45:14
Mr_Steady
Audiophile

Posts: 2042
Location: North Florida
Joined: August 19, 2014
 Panasonic DC Link at Mouser

100uf 500v 4 pin $21

Ten for $200. That's half the price of the WIMAs. Not too shabby.

Do all 4 pins have to be connected?


Big speakers and little amps blew my mind!

 

Scotch PS Caps, posted on December 11, 2014 at 19:12:49
Mr_Steady
Audiophile

Posts: 2042
Location: North Florida
Joined: August 19, 2014



Here are some Scotch caps for ya.

Russian electrolytic 100uf 350v caps. 10 for $15.

Are the connectors a pain?




Big speakers and little amps blew my mind!

 

RE: Scotch PS Caps, posted on December 12, 2014 at 08:49:27
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005
 The safest suggestion I have already made, was to use WIMAs, as they HAVE been sonically evaluated and determined to be superb !!

Cheaper DC LINK stuff, have NOT yet been sonically evaluated, and so, those cheaper ones may be more expensive !! :-)

I use the higher VDC rated caps, 800 or 900 VDC as I recall, and use in the C1 position ... it is fine !!

Jeff Medwin

 

RE: Scotch PS Caps, posted on December 12, 2014 at 09:39:51
Garg0yle
Audiophile

Posts: 859
Joined: December 1, 2014
 If the connectors work in your application they are fine. I would try and find out when they were made though as they are electrolytic.

Although if you are trying to achieve a specific grounding scheme, these may limit you as they will be grounded to the chassis at their particular locations.

Aside from that, what's not to like, simple and easy installation and only one wire to connect.
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RE: Circuit rev 2.2, posted on December 13, 2014 at 18:43:40
Tre'
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Location: So. Cal.
Joined: February 9, 2002
 Paul, what would happen if the bypass cap from the high side of the plate choke was connected to the cathode of the 6j5 instead of ground and the bypass cap from the cathode of the 2a3 was moved to the output side of the filter choke?

Stacked UPX2. That's a catchy name!

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: PS caps question , posted on December 14, 2014 at 04:39:38
Frihed89
Audiophile

Posts: 15703
Location: Copenhagen
Joined: March 21, 2005
 WIMA DC-LINK MKP4 or 5 or 6? Or what?

 

RE: Circuit rev 2.2, posted on December 14, 2014 at 11:00:57
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001
 First change would inject any hum at the cathode of the driver, instead of at the plate and attenuated by the plate choke impedance - so I would expect a lot more hum. It's a fairly easy experiment though ...

The second change is unclear; you appear to describe moving the 2A3 bypass cap to parallel the existing ultrapath cap?

 

RE: Circuit rev 2.2, posted on December 14, 2014 at 16:06:32
Tre'
Industry Professional

Posts: 17303
Location: So. Cal.
Joined: February 9, 2002
 "First change would inject any hum at the cathode of the driver, instead of at the plate and attenuated by the plate choke impedance - so I would expect a lot more hum. It's a fairly easy experiment though ..."

Ultrapath requires a very quiet PS.

"The second change is unclear; you appear to describe moving the 2A3 bypass cap to parallel the existing ultrapath cap?"

The ultrapath cap goes from the output of the PS to the cathode of the 2a3, not ground.

What I am proposing is to remove the 2a3 cathode bypass cap (it's not needed, the ultrapath cap bypasses the cathode resistor) and use it as a cap from B+ to ground in order to reduce the ripple of the PS.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: Circuit rev 2.2, posted on December 14, 2014 at 18:17:18
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001
 Yes, I am not following the ultrapath design exactly. The cap from cathode to ground does have an influence on the bass, I believe. In any case, ultrapath relies on the power supply impedance being large, i.e. the last element being a choke, so a cap to ground at the B+ is out unless you add in another choke.

 

RE: Circuit rev 2.2, posted on December 14, 2014 at 19:14:22
Tre'
Industry Professional

Posts: 17303
Location: So. Cal.
Joined: February 9, 2002
 "...ultrapath relies on the power supply impedance being large,..."

Ultrapath takes advantage of the power supply "path" impedance being large.

The impedance of the power supply path, even when the last element of the PS is a cap, is large (compared to the reactance of the ultrapath cap) because it includes the value of the cathode resistor.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: Circuit rev 2.2, posted on December 15, 2014 at 13:21:51
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001
 I can't locate an example, but I think in the original circuit there was a resistor between the power supply and the top of the output transformer. However there seem to be a great many variations all going under the Ultrapath name.

I'll change the name of the capacitor in the schematic, and edit my text to refer to "cathode-coupled" output, which I believe is a more widely accepted term.

 

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