Here it is ..All DHT stereo amp ..26-26 DC 45..

The 26 is a mighty tube, posted on January 17, 2015 at 15:39:34
Chip647 Audiophile Posts: 2651 Location: The South Joined: December 24, 2012	Any issues with microphonics?

RE: The 26 is a mighty tube, posted on January 17, 2015 at 16:51:29
deafbykhorns Audiophile Posts: 1067 Location: Florida Joined: October 17, 2003	Try it with rod colemans power supply

RE: Here it is ..All DHT stereo amp ..26-26 DC 45.., posted on January 17, 2015 at 18:19:30

Sidewinder
Audiophile

Posts: 254
Joined: April 13, 2001

Hello drummerwill,
Nice looking build. So how does it sound? You say modestly 'decent',but could you compare this with your other amps? Your general impressions would be nice.

I'm still trying to learn this stuff so if you don't mind, I have a few rookie question about your schematic. First, the schematic says for one channel, so I'm thinking monoblocks but your picture shows all the tubes on one chassis. Are there two or one power supplies? From the labeling I'm confused about the B1+ Lchn, B2+Lchn and B2+Rchn ??
Regards.
David

Corrected Schematic...., posted on January 17, 2015 at 22:41:36

drummerwill
Audiophile

Posts: 965
Location: St Louis Mo.
Joined: January 7, 2003

Sorry for the bad labeling on that one, this should better explain the design.

How does it sound compared to my other amps ?
Well it doesn't have the authority that my 6SN7-DC-2A3-IT-845 amp has nor the extended bandwidth of my 2A3 DC Parafeed amp. But what it does have is a very Clean sharp musicality across the bandwidth.
I mean you can hear the DHT front end driving the 45's. .... So crisp so clear. The type of reproduction of music you never want to turn off!

OK I've said too much . ..Sorry .... it sounds decent !

Willie

RE: The 26 is a mighty tube, posted on January 17, 2015 at 22:44:33
drummerwill Audiophile Posts: 965 Location: St Louis Mo. Joined: January 7, 2003	No problems I've heard . Willie

RE: Corrected Schematic...., posted on January 18, 2015 at 05:37:36
Jim Dowdy Manufacturer Posts: 1518 Location: Atlanta, GA Joined: July 22, 2000	The schematic shows no bias reference for the grid of V2. [R(g) or grid choke.]

RE: Corrected Schematic.... Thank you Jim ...., posted on January 18, 2015 at 07:50:35
drummerwill Audiophile Posts: 965 Location: St Louis Mo. Joined: January 7, 2003	for your suggestion. I can only tell you, I tried putting a grid resistor to ground on V2 ...it didn't work on my amp. I can only show what has worked for me and I think the circuit shown represents what I have now that is working. Again Thank you for your input ! Willie

RE: Corrected Schematic.... Thank you Jim ...., posted on January 18, 2015 at 08:55:39
Tre' Industry Professional Posts: 17302 Location: So. Cal. Joined: February 9, 2002	"I tried putting a grid resistor to ground on V2 ...it didn't work on my amp." So the amp runs and sounds good with no bias reference for the second type 26 tube? That's really interesting. I wonder what's going on there. Tre' Have Fun and Enjoy the Music "Still Working the Problem"

RE: Corrected Schematic.... Thank you Jim ...., posted on January 18, 2015 at 10:42:15
GEO Audiophile Posts: 4749 Joined: April 7, 2000 Contributor Since: September 9, 2000	Maybe this addresses what some may view as a compromised PSU design?

RE: Corrected Schematic.... Thank you Jim ...., posted on January 18, 2015 at 10:48:15
Caucasian Blackplate Industry Professional Posts: 8313 Location: Seattle Joined: June 18, 2004	What voltage is the grid of the 26 sitting at? What didn't work with the resistor?

Could you please explain to a , posted on January 18, 2015 at 12:18:40
91derlust Audiophile Posts: 1101 Joined: December 25, 2014	a learner how that could be the case? Thanks in advance. 91. "Confusion of goals and perfection of means seems to characterise our age." Albert Einstein

RE: Corrected Schematic.... Thank you Jim ...., posted on January 18, 2015 at 12:41:37
tube wrangler Manufacturer Posts: 2484 Location: USA Joined: January 29, 2007	Willie--- what was the value of the grid resistor-to-ground that you tried on V2? --Dennis--

My post didnt' have anything to do with the PS, posted on January 18, 2015 at 13:08:37

Tre'
Industry Professional

Posts: 17302
Location: So. Cal.
Joined: February 9, 2002

If the grid is not bias referenced (ie; some connection back to the cathode. Normally done with a resistor or grid choke to ground so the cathode resistor can provide bias for the tube or in the case of a direct coupled circuit the reference is back through the previous stage), the tube cannot work properly if at all.

Does anyone have any insight as to what's going on here?

The amplifier is reported as working and "sounds decent".

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

RE: Corrected Schematic.... Thank you Jim ...., posted on January 18, 2015 at 13:12:05
Tre' Industry Professional Posts: 17302 Location: So. Cal. Joined: February 9, 2002	What value resistor would be worse than no resistor? There's no such thing as too low, at least in terms of the function of the tube itself. Tre' Have Fun and Enjoy the Music "Still Working the Problem"

I'm with Tre'..., posted on January 18, 2015 at 13:45:06
Jim Dowdy Manufacturer Posts: 1518 Location: Atlanta, GA Joined: July 22, 2000	I'm still pondering how V2 functions as drawn.

RE: My post didnt' have anything to do with the PS, posted on January 18, 2015 at 14:52:23

gusser
Audiophile

Posts: 3649
Location: So. California
Joined: September 6, 2006

1) Bad V2 with internal resistance between cathode filament and grid?

2) Enough dirt or other substance on tube socket to act as a grid reference?

3) DC Leakage through coupling cap?

RE: Another ....Corrected Schematic...., posted on January 18, 2015 at 15:21:10
drummerwill Audiophile Posts: 965 Location: St Louis Mo. Joined: January 7, 2003	The correct value for the Bias meter resistor is 10 ohms !! Willie

Thanks, there has to be something................., posted on January 18, 2015 at 15:25:03
Tre' Industry Professional Posts: 17302 Location: So. Cal. Joined: February 9, 2002	otherwise I wouldn't think it would work at all. Tre' Have Fun and Enjoy the Music "Still Working the Problem"

Dennis I tried a 50K ......, posted on January 18, 2015 at 16:18:26
drummerwill Audiophile Posts: 965 Location: St Louis Mo. Joined: January 7, 2003	with that I got no sound ! It sounds decent without a Grid resistor ! Willie

RE: Corrected Schematic.... Thank you Jim ...., posted on January 18, 2015 at 16:22:18
drummerwill Audiophile Posts: 965 Location: St Louis Mo. Joined: January 7, 2003	Yeah Tre' It seemed strange after others had suggested I needed a grid resistor. But thatsit. Willie

Some basic questions, posted on January 18, 2015 at 16:56:34

Sidewinder
Audiophile

Posts: 254
Joined: April 13, 2001

Thanks for the corrections drummerwill. I want to build this amp, so please indulge me to ask a few basic questions.

1.)First, where should I connect the other primary line of the 5U4 filament transformer?

2.) Why are the B2+Lch (332V)and B2+Rchn (339v) voltages different and the voltage is 337v on the signal schematic?

3.) You show no values for the bypass caps. What are good starting values for the 26 and 45 tubes?

4.) There's a cap after the 24uf 630V in the PS with no specified value. Is it necessary?

5.) I would need two dual 26 supply, one for each channel, correct?

6.) Would two 5VDC 3A Wall Adapter Power Supply work for the 26 filament supplies or.. ?

7.) Two 2.5Vac transformers and associated caps and resistors, one for each channel are needed, correct?

8.) Can you direct me to a schematic for a LM335 based regulator? My searches shows the IC as a temp. sensor.

9.) I may have more questions later. I really need to build this amp!!

Thanks again for taking the time to share your work.
Regards,
David

RE: Dennis I tried a 50K ......, posted on January 18, 2015 at 17:10:48

Tre'
Industry Professional

Posts: 17302
Location: So. Cal.
Joined: February 9, 2002

"Dennis I tried a 50K ......with that I got no sound !"

That's a clue. I still don't know what it means but *no sound when a 50k grid resistor is in place* is a clue.

Do you have 2 channels behaving this way?

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

RE: Dennis I tried a 50K ......, posted on January 18, 2015 at 18:44:06
tube wrangler Manufacturer Posts: 2484 Location: USA Joined: January 29, 2007	Hi Willie. Try 350K, then try 250K. Let me know what happens. ---Dennis---

To All ......maybe I should have explained something first...., posted on January 18, 2015 at 20:19:50

drummerwill
Audiophile

Posts: 965
Location: St Louis Mo.
Joined: January 7, 2003

For me this amp was just an experiment into all DHT power in a cost effective way. The state that its in now is what has got me sound out of both the OPT's .

What the schematic represents is as complete q representation of what is on the circuit. That it actually makes such good music is amazing to me.

Now that it's out here on AA , offers anyone who wants to can take it from here. As for me, I'll only plan to get better OPT's..

Willie

RE: Some basic questions, posted on January 18, 2015 at 20:31:51
drummerwill Audiophile Posts: 965 Location: St Louis Mo. Joined: January 7, 2003	1) Not sure what you mean 2) Stupid record keeping mistakes. ( Shoot for approx. voltages) 3) This is not mine to give ! 4) not specified.... it's all DIY 5) Yes 6) Give it a try ! 7) YES 8) Google is your friend . 9) Please be careful ... and Have Fun ! Willie

Grid Self Bias..., posted on January 18, 2015 at 21:56:28
Ivan303 Audiophile Posts: 48887 Location: Cadiere d'azur FRANCE - Santa Fe, NM Joined: February 26, 2001	Who knew? First they came for the dumb-asses And I did not speak out Because I was not a dumb-ass

RE: Some basic questions, posted on January 18, 2015 at 22:34:44
Sidewinder Audiophile Posts: 254 Joined: April 13, 2001	Hello Willie, Thanks for taking time to answer my questions. 1.)On the filament transformer for the 5U4, I only see one connection on the primary side. 8.) Google must not like me. The only reference to a LM335 is a temp sensor. A little help Please. Thanks again, David

RE: Some basic questions, posted on January 19, 2015 at 06:21:04
drummerwill Audiophile Posts: 965 Location: St Louis Mo. Joined: January 7, 2003	Aww yes. must be a typo ... I think it's LM338 for a 3amp 3 term. V.R. CT of the 5V PT not connected. Willie

Where did the idea for this come from, posted on January 19, 2015 at 07:22:07
Frihed89 Audiophile Posts: 15703 Location: Copenhagen Joined: March 21, 2005	It looks unbelievably simple (good) on the signal side (not a lot of stuff in the way of the signal) to my non-DIY brain...and it works!

You guys were right !.. it needs a bias resistor ....., posted on January 19, 2015 at 12:30:42

drummerwill
Audiophile

Posts: 965
Location: St Louis Mo.
Joined: January 7, 2003

Yes it ( my Amp) will play without the bias resistor, but it will exhibit some instability.

This would show as one channel not playing at times, or would fade out sometimes when playing at highest volumes. Bias reading between channels were also different

I guess it really didn't start showing up until I started testing it more and moving it around a lot.

I installed a 100k resistor on the grid of each V2. Now both bias meters read about 28ma on the 45's and plays at full volume.

Thanks Jim Dowdy who spotted this problem a while ago ....!
I should come here ask for .... and listen ... to you guys more often .!!

Thanks All

Willie

RE: You guys were right !.. it needs a bias resistor ....., posted on January 19, 2015 at 12:54:48
Caucasian Blackplate Industry Professional Posts: 8313 Location: Seattle Joined: June 18, 2004	That's not where you need the bias resistor, you need it after V1.

RE: You guys were right !.. it needs a bias resistor ....., posted on January 19, 2015 at 13:56:18
RPMac Audiophile Posts: 377 Location: So. Mississippi Joined: January 3, 2005	Wouldn't that be at V2 after the coupling cap? V1 has a grid choke. Dennis suggested 350K or 250K.

Ok I screwed the schematic up again......., posted on January 19, 2015 at 14:10:51
drummerwill Audiophile Posts: 965 Location: St Louis Mo. Joined: January 7, 2003	after putting the 100K resistor in the wrong place. I'm not going to post that schematic again Willie

RE: You guys were right !.. it needs a bias resistor ....., posted on January 19, 2015 at 16:54:23
Caucasian Blackplate Industry Professional Posts: 8313 Location: Seattle Joined: June 18, 2004	Yeah, oops, after V1.

RE: You guys were right !.. it needs a bias resistor ....., posted on January 19, 2015 at 18:30:55

Tre'
Industry Professional

Posts: 17302
Location: So. Cal.
Joined: February 9, 2002

The larger you make the value of the grid resistor (within the limits of the tube) the happier the stage before it will be.

"I generally stick to grid leak resistor values of 250K or less with the 26 as they tend to have significantly higher grid current than more modern types.

Grid leak resistor values aren't given in any 26 datasheet I have looked at - probably because the 26 was commonly used in transformer coupled circuits. "

As a separate issue, with a 100k resistor and a .1uf coupling cap you will have a -3db point of that high pass filter at 15.9Hz. The amplitude and phase will remain somewhat disturbed clear up to 159Hz.

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

RE: You guys were right !.. it needs a bias resistor ....., posted on January 19, 2015 at 20:00:09

drlowmu
Manufacturer

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

With a 0.1 uF coupling cap, Dennis' suggestion, start with about 350K Ohms, listen and measure, then TRY 250K Ohms, listen to that, makes very good sense to me. I am glad Willie is open minded enough to give it a TRY !!

There may be a run on 5VCT at 3 A. wall warts, at local thrift stores, all over America now !!!

Jeff Medwin

The only way to tell if your amp is functioning right or not, posted on January 19, 2015 at 21:44:10
bouncy ball Audiophile Posts: 1221 Location: British Columbia Joined: July 26, 2003	is by using a signal generator and a scope, that is what I am learning now.

I think you might be right about that ...., posted on January 20, 2015 at 09:01:58
drummerwill Audiophile Posts: 965 Location: St Louis Mo. Joined: January 7, 2003	for most of my build I've relied on music input and speaker output. Thank you for your suggestion! Willie

RE: I think you might be right about that ...., posted on January 20, 2015 at 10:44:52

tube wrangler
Manufacturer

Posts: 2484
Location: USA
Joined: January 29, 2007

Willie:

Get it as good as you can musically. Your 100K is still too much load. When it's as good as you can get it, apply the signal generator and dual-trace 'scope.

Watch your thinking! You want signal replication, but NOT at the expense of any dynamics, speed, or transparency. You WANT IT ALL.

Keep going back and forth. After noting the test instruments, make necessary corrections and go right back to listening, then-- after a few weeks or so-- back to the tests, etc.

When you think it's good, call-in your NON-audiophile friends and throw a Party. They will tell you if it's good or not.

The audiophiles can come in and grasp at it after it's perfected. Until then, let them pontificate with their own stuff.

Here's a little story to encourage you-- and other good guys here: A while back, I attended VSAC in Washington State. There were only 35 or 36 exhibitors there.

It was mainly a DIY affair, but was open to us semi-commercial guys as well.

There were all kinds of DIY people present, and a contest downstairs to see who could build a SPUD amp in a day, or so-- or was it hours? Don't remember. The DIY guys did it, and it sounded OK to me. They're pretty talented!

I had my usual demo going on with the big GPA 604's in a terrible room with a huge ceiling vault, and really bad echo/acoustics. So, I dutifully placed the two speakers very close together-- in a huge room, no less, and killed all the bass I could because the room was just too big and echoey to control. No hope for my time and budget!

So, we just set it up so we liked the music-- to "H" with the @@#$%^ room!

I knew this was no show-winner, but we were having fun anyhow. I just let it play and cruised around the other places, enjoying the DIY stuff, and all the cool LP's one could purchase.

I got back, and the Hotel crew (that was on a break) was in my demo room. They had been to all the other rooms, and liked this one-- said it sounded "real" to them-- the others didn't. They loved it, and over the next few days, the whole Hotel crew was spending every off-moment in our demo room.

The DIY people and Audiophiles didn't care too much-- they said good amps, bad demo, etc. They were Nit-Picking, the normal people were enjoying music despite the room.

If you're developing equipment to listen to, you have to decide what is real.

---Dennis---

RE: I think you might be right about that ...., posted on January 20, 2015 at 12:27:10

GEO
Audiophile

Posts: 4749
Joined: April 7, 2000
Contributor
Since: September 9, 2000

Thats when you know you are on to something

Good listening session

RE: I think you might be right about that ...., posted on January 20, 2015 at 20:26:46
tube wrangler Manufacturer Posts: 2484 Location: USA Joined: January 29, 2007	Thanks, George-- good Banjos. reminds me of Southern California. I like it! Speaking of S. Cal., you might like these CD's-- Chris Hillman and Herb Pedersen at Edward's Barn (Rounder 11661-0652-2), and Chris & Herb-- "Bakersfield Bound". ---Dennis---

RE: You guys were right !.. it needs a bias resistor ....., posted on January 21, 2015 at 05:46:25
Alpha Al Industry Professional Posts: 2958 Location: N. Carolina Joined: February 16, 2004 Contributor Since: December 3, 2015	I would expect that 26 tube to draw heavy current and maybe self destruct without a grid resistor to ground.

RE: You guys were right !.. it needs a bias resistor ....., posted on January 21, 2015 at 06:57:17
drummerwill Audiophile Posts: 965 Location: St Louis Mo. Joined: January 7, 2003	That didn't happen, but they did play music ! Willie

RE: You guys were right !.. it needs a bias resistor ....., posted on January 21, 2015 at 08:16:30
drlowmu Manufacturer Posts: 9730 Location: East of Kansas City Joined: January 10, 2005	TRY 350K - give or take 50K, grid to ground, second Type 26 !!! TRY it . Jeff Medwin

Yup 330K already done......., posted on January 21, 2015 at 20:08:27
drummerwill Audiophile Posts: 965 Location: St Louis Mo. Joined: January 7, 2003	Sounding pretty good ! Willie

RE: Yup 330K already done......., posted on January 21, 2015 at 21:44:09

drlowmu
Manufacturer

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

Should be fine now. You are there Willie !!! Congratulations.

Happy you posted on this Forum for all to see your own amp, schematic, and to comment upon !!

Jeff Medwin

It was that crazy instability thing ....., posted on January 22, 2015 at 14:55:39
drummerwill Audiophile Posts: 965 Location: St Louis Mo. Joined: January 7, 2003	That plagued me after I added the second 26 ..But it appeared so randomly it had me fooled. Now she's as solid as a rock , has plenty of gain with No pre. But with an active pre it just slams. What kills are those Hammond 125ESE's. They are such a bargain for bringing a project forward. I'm happy with the results of this experiment,I hope others will give it a try. Have fun Willie

When the smoke clears, it would be nice, posted on January 23, 2015 at 01:24:09
Frihed89 Audiophile Posts: 15703 Location: Copenhagen Joined: March 21, 2005	If you could post (or send me) the final schematic.

SET Asylum

Here it is ..All DHT stereo amp ..26-26 DC 45..

99.5.232.186