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In Reply to: RE: The last 26-26 DC 45 amp schematic .... posted by drummerwill on January 23, 2015 at 12:04:05
Just for a comparison, here's an input section I tried previously. Sounded good! I always use interstages and filament bias - no coupling caps or cathode bypass caps. I discarded the 26 front end when I swapped to PSE 4P1L finals since I didn't need the gain any more. 4P1L has a mu of around 10. 4P1L is a more dynamic driver with better treble than 26 - it was a clear improvement to me.
Edits: 01/25/15Follow Ups:
Andy,I compute 3.39 Watts 4P1L anode dissipation on a 7.5 Watt plate. I like that for long term stability, IF I figured it correctly. Nice.
What would happen if one gave the Type 26 a grid to ground choke, as Willie does, ( rather than 100K to ground ) and direct coupled it into the second ( 4P1L ) stage with three runs of 19 AWG silver wire ?? What about your use of a 390 Ohm grid stopper, necessary ??, many go direct-in !!
Just thinking out loud.
Jeff Medwin
Edits: 01/25/15
I've got nothing against grid chokes. And the grid stopper could be omitted if you don't have any stabillity issues. I just put it in for security.
If you direct couple to the 4P1L you then need to ditch the filament bias and use a bypassed cathode resistor. Yes, for sure it's one way of doing it, but I just don't like cathode bypass caps. With my 4P1L> PSE 4P1L amp I just have 2 stages, so I don't have a 26 stage to couple, so that eliminated the issue completely. It sounded cleaner with 2 stages for sure, and I really like 4P1Ls as outputs. You're a bit stuck with the 45 since you don't have the 4P1L's mu of 10, hence the need for 3 stages.
I understand your comments on Rk bypasssing. Dennis Fraker is the only person ( I have seen ) who really can do that well, and he KNOWS how to do it. Its been in every one of his Serious Stereo amps, since 1989. It takes thousands of dollars to do properly, so most DIYers never attempt it !!It requires a main Rk film cap, of a not too large value, and then, a large number of additional smaller value caps, only of the highest quality AND importantly - the correct specific uF values, to optimally execute a bypassed Rk.
Its been very much FUN ( for me ) to hear the result, when its properly
done !!One other thing I fully concur with you on, a two stage amp, well done, will ALWAYS be better-sounding, more transparent sounding, than ANY three stage amp !! Do that !!
Jeff Medwin
Edits: 01/25/15
Wait a second, doesn't Andy's amp have less stuff in the way of the audio signal than the SS 2A3? And i thought that was the whole rationale of DC amps.
Observe, before you think. Think before you open your yap. Act on the basis of experience.
Heck no, Andy is going through iron ( interstage transformers ) in SERIES with the signal, whereas we direct couple one tube to the other with 3 pieces of 19 AWG finely-made silver.
One could say, in a SE amp, every part is in the audio signal.
Now, for Rk bypasses, THAT does take a LOT of parts to do it best, going from the top of the Rk, to ground !!! Those highest quality, expensive parts are MIA in your DC amps BTW. Foremost, the amps' designers never knew how to work with them!! But done right, I can tell you, they are essential to include, I LOVE them and what they do. Only DF, to my knowledge, knows to do this, and he executes it first-class in every piece he puts out. YOU can't judge that with one RMAF visit, where we are not always set up well. It took multiple venues and set ups for me to listen and figure this all out. But I am very very SURE of what he builds, and how it plays.
The most recent news is that Dennis' latest amps, he has four built, building four more, are totally unequaled with anything he, or anyone else for that matter, has done to-date in tube audio design. They are simply ...wonderful . Drummerwill, Corona Dope, and I got a "taste" a "preview" of this with RMAF 2013 on Sunday morning, before tear down. Blew us good listeners away, and ... it is certainly well beyond that, right now.
Some of this, I am hoping, will fall into my hands, with my home amps. Hell, I have ALL THREE of my DC two stage amps torn down presently, waiting for my rebuilds with latest ideas and parts !! Progress is being made. If I can come within 50-60% of what DF builds today, I will be a very happy camper.
There is the very latest in audio news, sir !! Capish??
Jeff Medwin
A word or a few of explanation seems necessary here, Jeff.RMAF 2013 was after the Pine Creek forest fire out here, which wiped-out my shops, all amps, and parts.
Since I had no amps of any kind-- even to listen to-- a friend loaned me a pair of amps that I had delivered in 2006. Berkeley Audio Designs fixed me up with a new Alpha-DAC2 with their USB link. (NO!-- I wasn't interested in anything else!). My music server P.C., which had been built for me in Virginia (Command Performance) was saved because the guy had had it there for a week! I got lucky there....
I quickly borrowed from him the Triple 12V. power supply that I build for P.C.s to make them come alive. I got it, photographed it's insides, and sent it right back. This saved a lot of time, as all my papers were gone.
I had that, and a Panasonic Plasma T.V. I got at Costco with an equipment rack. I quickly ordered (from a guy on E-Bay) a Pioneer BDP09-FD Blu-Ray player, knowing that the SPDIF on this 30 pound (strong, stable transport) baby could deliver good sound thru the Alpha-DAC2, and it did!
Sooo--- RMAF 2013 was the year I decided to do Blu-Ray-- since I had this rig! I Played The Eagle's farewell Tour-- Melbourne, Australia. This is GREAT audio!
Did audiophiles and reviewers applaud this departure into Blu-Ray? I think not.....!
Was this setup ideal? Hmmmmm!! BUT-- I, and I think quite a few others had a great time! I remember watching Joe Walsh and wishing we were serving Beer.... WHAT a GREAT voice! Hey! Blu-Ray is good! Don't knock a medium-resolution source with a great band that has good equipment....
Since I had no amps or shops, everything is all-new, and so are the latest amps. I got the opportunity to change anything I wanted to, and to buy any parts I thought were superior... They ARE!
The 2006 amps went back to their owner. I spent a couple thousand bucks on them, and charged nothing. I was already doing new engineering, so I just did it--- and really appreciated that he got me thru RMAF 2013...
The man called up and was deliriously happy, but so was I! I had gotten to use his amps while I engineered new stuff!
Well, you haven't heard the new stuff. Few people have yet. I hope to do RMAF 2015. Maybe.... we'll see.
---Dennis---
Edits: 01/25/15
"If I can come within 50-60% of what DF builds today, I will be a very happy camper."
Please, so many of us are sick to death of hearing about what your idol DF has been doing, and how wonderful his amplifiers are. Can't you just give it a break? He's just an average chap, making average quality home brewed amplifiers.
There are a few of us who appreciate every comment and every scrap of wisdom that Jeff brings to the forum and those of Dennis too.
Jeff has mentored me in building my own amp and now have what I consider a stunning amp with breathtaking sound. I admit it may only reach 50% of what a SS amp achieves but I'm having great fun building and listening to this amp.
It does cost money and that is perhaps why many DIY builders do not attempt it. With hindsight it may have been easier and cheaper just to purchase a SS amp but I wouldn't have gotten the pleasure of building and learning.
I'm trying to get others here in London to listen to my amp so they have an accurate opinion of its attributes but so far no takers.
All I ask of a forum and its members is courtesy and manners.
Is that too much to ask.
Smart
> Jeff has mentored me in building my own amp and now have what I
> consider a stunning amp with breathtaking sound.
We are glad you are happy with your build.
> All I ask of a forum and its members is courtesy and manners.
> Is that too much to ask.
Not much. But how about other forum members who don't appreciate let's say politely - engineering not based upon laws of physics, which have been propagated through 8500+ posts, with the addition of 1500 long and meaningless messages from his "teacher"???
Do these man have anything else to do apart from flooding forums???
Their wives and kids must be proud of them
"I admit it may only reach 50% of what a SS amp achieves but I'm having great fun building and listening to this amp."
We need to stick together!
Actually, though, I fear you are right, although I would say "some SS amps". However, I am taking cold showers and using other monastic remedies to rid myself of any such thoughts. But my experiences with a small number of SS systems are hard to drive out of my mind.
Observe, before you think. Think before you open your yap. Act on the basis of experience.
I have known Dennis for three decades plus. I know the man.
The way he is talking to me about his newest builds, I am pretty darn sure they will be a total sonic treat for people to hear !!!
This is a wonderful development, IMHO.
( As a personal note : It also calms me, when I think ALL THREE of my two stage DC SE amps are ripped apart, waiting for my copy-cat parts and wiring upgrades. )
Have a great day !!
Jeff Medwin
What hobbies do your wife and kids have?
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