Hi,
thank you for you cautionary comments. but then again, attempting PFB on an NFB triode amp sounds like a challenge, another one for the distant future perhaps. The bones of the circuit I am concocting looks more like this, where Q1 is a triode and Q2 is a pentode. I have developed a variation on this in my day job, sans tube, and it works quite well, +-20A, 1MHz bandwidth.... The challenge I haven't quite got round elegantly for an audio application is the input being way from ground, and how to do dc coupled feed back, and now some positive feedback as well. I suspect the solution will have several zener diodes and some well behaved power supplies in the short term.
thank you for you cautionary comments. but then again, attempting PFB on an NFB triode amp sounds like a challenge, another one for the distant future perhaps. The bones of the circuit I am concocting looks more like this, where Q1 is a triode and Q2 is a pentode. I have developed a variation on this in my day job, sans tube, and it works quite well, +-20A, 1MHz bandwidth.... The challenge I haven't quite got round elegantly for an audio application is the input being way from ground, and how to do dc coupled feed back, and now some positive feedback as well. I suspect the solution will have several zener diodes and some well behaved power supplies in the short term.
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This multiplied by 1000. I built a proto board version in less than one afternoon to measure open loop behavior and experiment. It is 4 transistors and a few resistors. ...and I have never built an amplifier from scratch before.
If you require a spoon-fed amp, purchase an F5 kit from the DIY store. You can get all the parts and boards. I bought the complete set and will build one soon.
I found the F7 scheme on the Polish forum.
Reverse engineering wzmacniacza FirstWatt F7 - schemat - fakcior blog | DIY, Elektronika, Audio, IoT, Smart Home
This looks like a very likely layout of the First Watt F7.
Mr Nelson Pass, is it like that?
Reverse engineering wzmacniacza FirstWatt F7 - schemat - fakcior blog | DIY, Elektronika, Audio, IoT, Smart Home
This looks like a very likely layout of the First Watt F7.
Mr Nelson Pass, is it like that?
Similar. The F7 doesn't use an output zobel network and they didn't
include the PCF. I didn't check the values.
The F7 with laterals and Jfets is essentially the ProFet brought to you by
Selectronics, unfortunately not made for some years.
Actually, they had a bit more crap in it, but when you strip it to the bone...
And my contribution was the positive current feedback, so we can hardly
criticize an effort that lacks the pcf, can we?
Selectronics, unfortunately not made for some years.
Actually, they had a bit more crap in it, but when you strip it to the bone...
And my contribution was the positive current feedback, so we can hardly
criticize an effort that lacks the pcf, can we?
The F7 with laterals and Jfets is essentially the ProFet brought to you by
Selectronics, unfortunately not made for some years.
Actually, they had a bit more crap in it, but when you strip it to the bone...
And my contribution was the positive current feedback, so we can hardly
criticize an effort that lacks the pcf, can we?
Interesting amplifier
6moons.com - industry features: Zen amps
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Actually, for a bit I thought I had invented the name....
But I always assumed that it had been explored at some point in the
past, as it was just too obvious.
A New Look at Positive Current Feedback, November 1957 Radio & TV News -
RF Cafe
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