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57.66.65.3
In Reply to: RE: It's Alive! posted by Triode_Kingdom on March 03, 2015 at 22:20:09
I did a PP amp with these many years ago
Al
Follow Ups:
I don't want to identify the exact tube type until I'm sure I have enough. I've seen prices for this or that tube really jump after someone on a forum like this one started talking them up. Anyway, I don't know yet if this design will prove entirely successful. Frequency response isn't what I was hoping for, and I need to determine the cause. My first thought has to do with filament-cathode capacitance at the output stage (it's a follower), but it could be something else entirely. I'll know more after a little more work this evening.
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Buy Chinese. Bury freedom.
This turned out to be the output transformer. It's an inexpensive 5K:8 that I've frequently used for prototyping small single ended pentode designs. Its shortcomings are more apparent in an all triode amplifier like this with no NFB. I've minimized the response problem now by loading it differently. Originally, with an 8 ohm load, response was down about 3.5 dB at 20 kHz. With a 16 ohm load, it's only down about 1.5 dB. Output power doesn't suffer drastically with this change, about 0.65W VS 0.50W. Next step is to test with music, then check harmonics. :)
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Buy Chinese. Bury freedom.
> > My first thought has to do with filament-cathode capacitance at the output stage (it's a follower) < <
Is it really a follower? If the anode is at ground potential while the cathode at a negative one, it would not be a follower if the input is referenced to ground. For all intents and purposes this would be a grounded cathode stage, only turned upside down - or so I think.
" If the anode is at ground potential while the cathode at a negative one, it would not be a follower if the input is referenced to ground."
The primary of the output transformer is in series with the cathode. The grid is referenced to the bottom of that primary. The anode is grounded for AC. So, it's a follower, but with a twist - the anode is also grounded for DC. That renders the exposed anodes safe for my livingroom. :)
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Buy Chinese. Bury freedom.
> > The grid is referenced to the bottom of that primary < <
Then yes, it's a follower. I thought that you had actually referenced the grid to ground, hence my comment.
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