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In Reply to: RE: Forget the technical summary.......( long ) posted by drlowmu on August 18, 2007 at 18:22:37
Hey Jeff - In regards to speakers, I have at least one pair that are 100 db or more (15" University coaxials) so I should be OK. I don't usually listen that loudly anyway. My only previous DIY amp is a SE 45 so the PP 6B4G should have plenty of power compared to that.
Of course I will, no doubt, come to my own conclusions ultimately since I plan to experiment a bit with this amp. But it's nice to have some specific suggestions on things to try and I welcome all you guys' experience and knowledge regardless of whether it's based on "by the book" technical theory or purely on listening.
I am trying some of your ideas with the PS. I'm using a single Signal power transformer and separate rectifiers and LCLC sections (one Triad C-40X and one Stancor C-2708 in each) for the outputs and inputs.
One variation is that I'm using hybrid rectifiers for the B+ sections. UF4007s on the negative side with snubbers and 5AR4 on the positive side. I know you dislike the 5AR4 but I like the idea of a gentler start up. I'm sure I'll try 5U4s too, since I have some of those. Of course I'd have to use different power transformer taps to adjust the B+ higher since the 5U4 will drop considerably more voltage. Some of your other rectifier suggestions like the 5V4G and 5V3 would require even more changes.
. . . Charlie
Follow Ups:
Fla Charlie,Well....It is nice for me personally, to know that you are trying out the power supply.
1) Did you have a different supply in your 45 amp previously, and if so, what did you notice, if anything, when going to the "lower everything" supply ??
2) Did you implement it with heavy AWG wire of high quality? Was the C1 and C2 at 50 uF or so??
You will find P-P to be MUCH more forgiving of parts choices, etc. compared to SE, which is unforgiving and thus I think, seldom done optimally.
Jeff Medwin
Jeff - the PS mentioned is what I'm using for the PP 6B4G. The caps are 50uf motor runs for the B+ sections. One front end I want to try uses negative voltage for a LTP. That section is all SS - a FW bridge using Schottky diodes then CRC to the tail using Panasonic caps. Input tubes will either be 2C22s or a combination of 2C22 and 6SN7. I'll probably try a couple front end ideas but those are the tubes I want to try. The link below covers some of my questions about front end possibilites (if you have the time to read it - it's long). I think you were "on vacation" at the time. That thread was then continued briefly at:
http://www.audioasylum.com/cgi/t.mpl?f=tubediy&m=125544
By the way, when you suggest heavy AWG wire, what guage do you call heavy? And which connections, in particular, do you use this for? Everything? I've been using the regular hook up wire I have on hand.
The SE 45 (the "Bugle" design by Gordon Rankin) was built according to his schematic but with scrounged iron. I call it the "Budget Bugle". Power tranny came from a 1930 Philco. Output transformers were made by Stancor and came from a Wards console that ran SE 7868 outputs. So definitely NOT done optimally!
. . . Charlie
Fla Charlie,
The FIRST thing you want to do is treat the cathode with some deserved respect and NOT give it a choke input CLC power supply !!!!
Lets TRY to make it good, not such an obvious screw up!! L/C/L/C for the negative supply, OR... L/C/R/C only please !!
Good quality heavy AWG wire is the Siltec Silver 13 AWG wire. Price it and you will exclude 97% of the world's DIYers. I would say, 12 AWG as a minimum, maybe 10 if possible, stranded or a litz type.
But but but, you lose highs with this big of a common wire, so you need to parallel a single strand of TINY AWG wire, like magnet wire, across the 10 or 12 AWG, to get a balance. I would use this for all B+ distibution wiring, and for all ground return wires.
In my Eico HF-81, I listened this year to diferent wiring. I had 12 AWG silver stranded, with about 30 AWG Continuous Cast Copper magnet wire in parallel, and, after break in, it was OK. I actually preferred ( over the silver ), some Fulton Brown speaker wire, about 10 AWG, with a single 30 AWG CCC magnet wire strand in parallel. But, the Fulton Brown wire is not readily available to most people, so I am not so sure what to tell you that is cheap yet great.
One cheapo answer, UNTRIED by me, is at Radio Shack. They make a 12 AWG speaker wire, stranded copper called MegaCable, and they also offer fine AWG magnet wire, and heatshrink. I use about 1/2 inch sections of heatshrink, spaced every four inches or so, to parallel the fine magnet wire to the heavy copper speaker wire. That maybe beomes your on-a-budget starting point, subject to experimentation oin the future.
For audio signal wire, use Kimber's TCSS by all means, a best buy, safe choice. In certain places, like off of plates and especially in a direct couple, I will parallel two or more ( as many as four ) runs of TCSS, configuration selected by ear, sometimes with a single strand of magnet wire as a bypass.
I also think Wonder Solder is good sounding. Use it with GOOD ventilation, and please do not breathe its fumes. Position your input RCA jacks within two inches of wire lead length to the grid of the input tube. Do not ever " bundle" wires with tie wraps, etc.
Jeff Medwin
Thanks for the suggestions Jeff. When I posted earlier asking for suggestions for the negative supply, Ray Moth suggested I use a choke in place of a resistor in the CRC. For the voltages I had given in the post (probably not accurate) he thought a 1k resistor might be in the ballpark.
Whatever the value of the resistor turns out to be (let's assume 1k) are you suggesting that a choke with a 1k DCR should be used in a LCRC configuration? Or an LCLC using chokes with DCR of 500 ohm each? Or do you suggest using a low DCR choke in LCRC even though it must be followed by a higher value resistor to get the voltage into spec?
I'm not sure what I'll end up with but I'd like to hear your ideas on this.
As for the wire suggestions, I may experiment with that later or maybe not go quite as large. As a practical matter, how do you connect that large a guage to a standard size terminal strip or socket pin - especially considering that there are usually other leads from resistors, caps etc attached to the same place?
. . . Charlie
Fla Charlie,
Optimally speaking, the Cathode negative supply should be designed just as good as the Plate's positive supply.
Forget 1K resistances, in R's ..... or in Ls.
This past week, someone posted a schematic on an Eico vintage amp, and they were using ( back then !! ) 13 ohm Rs between caps on the negative supply, and, as I reall, 100 uF for the C's. Ray Moth sub-posted to it I recall. Everyone seemed to miss the point of the 13 ohm Rs, never openly commenting on that value, which, in MY MIND, is to maintain low series-resistance in the Cathode's negative power supply.
On thick wire, you tin the ends first, and then solder it where needed, using WONDER solder...no problem at all. How do you expect to keep intact the peak dynamic crests of the music, and "copy " the " low everything " supply implementation, if you change the parameters - and wire it with chintzy JUNK !!!!!!, especially after I almost ALWAYS post up here, " use heavy AWG, highest-quality wire ??.
Do it right, the first time, its NOT a budget breaker as there was just suggested for you a Radio Shack wire option .
Jeff Medwin
Jeff - Actually, I was the one who posted the schematic of the negative supply. It's not an Eico, by the way, it's a Scott 299B. I also posted an Eico HF-87 schematic and asked for comments on the viability of the 6SN7 portion of its input section as a possible input for the 6B4G amp since I want to use 2C22s (half a 6SN7) or 6SN7s or some combination of the two.
I have a rather large collection of vintage amps. The DIY interest came along with my doing restoration/repair on the old stuff. Out of all the vintage amps I have there are only a few that use fixed bias or some kind of negative supply - the Pilot 260, Dynaco ST-70 and the Scott 299B. I just posted this as an example of a negative supply, not with the intent of copying it.
The resistors are actually 18 ohm each and preceded by a 10 ohm, so don't these result in 64 ohms? That's a far cry from 1k, but as I said, the 1k was just an example. Hopefully I'll be able to come up with a combination of primary and secondary connections with the Signal transformer that will get me close enough for both the two B+ sections and the negative section that I won't have to use high value resistances. Mikeyb suggested previously that the Eico HF-87 input voltages could be adjusted and doing so I would need -125v to the cathode resistor. That's what the negative supply will be for.
I don't know what the Scott engineers were up to in this design somehow I don't think it had anything to do with "low DCR" since you'll notice in the Scott circuit there's also another leg with an 8.2k in it. So neither of these values are truly "low DCR" in your book. Correct?
I'll try to experiment with some heavier wire but, honestly, I wonder if 12 AWG wire will even fit through a standard tab on a terminal strip even by itself, not to mention on a tab that has other parts on it. I'm not sure if I even have any 12 guage around but I'll maybe try a pair of 16s or some 14 to see if it might fit.
I know there have been a couple of other guys who have built the "low everything" power supply. One, I believe you mentioned yourself, and you noted that he was pleased with the results even though he hadn't used heavy guage wire. Hasn't John Swenson (who I believe is a very experienced builder) built this PS too? Did he also employ your heavy guage wire strategy?
I'm going to be trying out various people's ideas in the process of building this amp, not building it according to, or trying to prove or disprove, any one person's theories. Sorry if that disappoints you. My purpose is to learn from it all and, of course, to hopefully end up with a great sounding amp. In the end, ALL of you guys will probably be able to call me an idiot and say, "There's NO WAY that could sound good because of . . . X, Y or Z." ;^)
. . . Charlie
"Optimally speaking, the Cathode negative supply should be designed just as good as the Plate's positive supply. "
Don't you mean the grid's negative supply?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
No.
JM
Jeff, will you take time to explain to me what this cathode negative supply is for?BTW, the negative supply and schematic FlaCharlie is talking about is for a Scott 299B. The negative supply is for the grid bias of the output tubes. It also runs the heaters in the preamp tubes. But no cathodes!
Thanks, Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Hi Tre' - I'm the cause of your confusion. I just posted the Scott schematic as a general example of a negative supply. The negative supply I want to try will supply -125v to the cathode of the input tubes.
In the post linked below, I posted a couple of input schemes and asked if they could be used for this PP 6B4G amp I'm building. One was a paraphase which someone had once suggested I could use as the input for a modded Dynaco ST-70. I also posted this schematic of an Eico HF-87, which uses one 6SN7 and one section of a 12AX7 per channel. I wondered if the 6SN7 section (only, no 12AX7) could be used. As stated previously, I want to use some 2C22s in this thing since I've read some posts which praise them highly. Mikeyb suggested that I could adjust the voltages so that the grid would be at 0v, the plate would be 180v and the cathode would be 5v and this could be accomplished by hooking the cathode resistor up to a negative supply. I'm not sure if this is really a LTP or a quasi-LTP or what since my technical knowledge is limited. Anyway, that's what the negative supply will be used for. I'll be using cathode bias on the outputs.
I'm not sure if either of these inputs (paraphase or the modded Eico) will work correctly but I may try them out. If I could get one of these to work I can use four 2C22s - two per channel. It was later suggested to me that I would have better luck using one 2C22 (half a 6SN7) and one 6SN7 per channel. I'm still open to suggestions . . .
. . . Charlie
Sorry, I missed all that.
Ralph does something similar with his OLT driver cathode follower so the output tubes can be both direct coupled to and biased by the cathode follower.
And yes, I agree with Jeff. That negative supply (or at least the last cap) is in the signal path.
Have fun, Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
"That negative supply (or at least the last cap) is in the signal path."
Suppose there's a CCS in the tail. How much signal gets through?
I know from experience that power supplies are more important than it seems they should be, and in ways that it seems they shouldn't. But, if we rank things in order of importance, I think the negative supply under a LTP is way down the list. The longer the tail, the less important it becomes.
-- Dave
As I mentioned, I'm not that familiar with negative supplies since only a few of my vintage amps use them. Probably a dumb question, but: All the schematics I've seen show an electrolytic cap with polarity reversed, as in the Scott I posted. Is it possible to use a non-polar motor run in a negative supply?
. . . Charlie
The polarity of the electrolytics in a negative supply is not reversed. Negative is connected to negative and positive is connected to positive, as in any PS. What is 'reversed' is the 'common' or 'ground', which is the negative line of a positive supply and the positive line of a negative supply.
So, can I use a motor run (non-polar) cap in a negative supply or do I have to use a polarized electrolytic?
. . . Charlie
Motor run caps would be fine.The reason the caps in a negative supply look upside down is the voltage is upside down. If you use a polarized cap, the + needs to go to the positive voltage point in the circuit and the - needs to go to the negative voltage point in the circuit. No matter where those voltages go.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
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