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In Reply to: Re: Capacitance in early vintage amps ..... ( Long) posted by Joelt on November 27, 2004 at 20:05:05:
Did you know that this is not a 'feedback' amp?I didn't think so.
Follow Ups:
Please post the schematic, or point to a location on the web.thanks.
Please post a schematic or link to any jukebox amp with PP triodes made by any manufacturer during the 30's that uses negative feedback, then we'll talk.
Actually the concept applies to non-feedback amps as well.
Didn't know that?I didn't think so.
"Actually the concept applies to non-feedback amps as well."Joel, your original response to Willie was that he should be careful or he might screw up the delicate balamce of the feedback loop.
BTW: Any tone or attitude in my posts was just an imitation of your own. I probably shouldn't post right after getting home from work, but I have nothing to appologize for.
> > ...your original response to Willie was that he should be careful or he might screw up the delicate balance of the feedback loop. > >Nope. Didn't mention feedback loops.
"Are you aware that many of these old feedback amps were designed so that all the power supplies had the same time constant?"
Cigna reading retention score: F
Certainly the implication of what you did write in your original response to the question is that the various power supplies were designed to have the same time constant in order to facilitate the proper function of the feedback circuit(s). This is the way I (an intermediate neophyte) interpreted it. It seemed to make sense that preserving the time constant would be a good thing to do in association with applying NFB. So, Cigna gets at least a B+.
It's probably worth nothing that if you are trying to avoid LF instability in a feedback amplifier, perhaps the last thing you want to do is have all the supply sections have the same time constants.-Henry
> > It's probably worth nothing that if you are trying to avoid LF instability in a feedback amplifier, perhaps the last thing you want to do is have all the supply sections have the same time constants. > >Not the "supply sections" Henry, but the different supplies - ie. negative grid bias for output tubes, B+, any screen supplies, etc.
Joel
so what kind of feedback were you referring to?.
Have Fun and Enjoy the Music
"Still working the problem"
I don't have a scaned copy of the schemo. But its a Wurlitzer jukebox amp model 661. Its a type 30 : tone control : 30 RC 45 IT 45 PP. Its an early model no feedback in the circuit. The power supply is a CLC with taps for DC filaments of the 2 30's and the first driver 45, kinda neat !
Willie
It does sound like a pretty cool amp. It's interesting that the RCA data books of the time often offered 'typical operation' of power tubes in PP with the same tube type as driver with an IT phase splitter. No, I'm not saying that the Wurlitzer amps are straight out of the data books, I just think it's interesting to see examples of the common thinking of the time.Of course Sakuma gets all the credit for thinking up 'like drives like' in SE. ;-)
-- Dave
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