AndreasS said:
I tried various amounts of gNFB. 20db(v) gave a very solid statey sound that wasn't any better than the Big Box SS amp I was using for comparison. That lasted for a few minutes before I got that out of there. 12db(v) was a little better, but not by much. 4 db(v) added the necessary clean-up, and definitely helped woofer damping. With a good, low distortion open loop front end, which I have, and decent OPTs, you don't need a whole bunch of gNFB since there's nothing grossly wrong that you need to cover up.
Dropping C5 will lower input sensitivity, and as a bonus increase the effective resistance of the driver tube which increases its effectiveness as a V-I converter.
pm
eatin' ol' bean again
I wonder if an OPT of higher impedance than 2K5 would be necessairy here. As per A. Kitic "..the main theoretical reason why those amplifiers sound good is the drastically lowered internal resistance of the output tube. One of the main factors determining the factor by which the internal resistance (output impedance...) will be lowered is the transconductance (Gm) of the output tube in question".
I wonder if an OPT of higher impedance than 2K5 would be necessairy here. As per A. Kitic "..the main theoretical reason why those amplifiers sound good is the drastically lowered internal resistance of the output tube. One of the main factors determining the factor by which the internal resistance (output impedance...) will be lowered is the transconductance (Gm) of the output tube in question".
Yes, the KT66 power tube works fine in the Tubelab SSE. I use the new Russian production Genalex KT66 in
mine and am very pleased with it. The SSE can also be operated with 6L6, KT88 and EL34 power tubes by
using suitable cathode bias resistors.
Man, am I late or what ??
I now realize that I have responded to an almost 10 years old post.😱
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This is an example of why there is no such thing as "time." Atoms are only rearranged, and we live in a place where there "is" no past and no future.
Ah, but time does allow some of us to be able to learn things like basic SPICE simulation.
I put the circuit into LTspice and saw that open loop, the amp as presented has extremely poor frequency response, with a severe roll-off of high frequencies. Add the negative feedback and the high frequency response is restored. So, rather than being a somewhat linear amplifier that has been made better by adding loop NFB, it relies on NFB for flat frequency response.
Wouldn't it be better to design a basic pentode SE KT66 (or 6L6) circuit that performs passably well, and then add the NFB to make it perform better?
Or is the drooping open loop frequency response intentional, and necessary for proper closed loop operation of the circuit?
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PS - Tubelab SSE and SE use a triode first stage, not pentode.
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I put the circuit into LTspice and saw that open loop, the amp as presented has extremely poor frequency response, with a severe roll-off of high frequencies. Add the negative feedback and the high frequency response is restored. So, rather than being a somewhat linear amplifier that has been made better by adding loop NFB, it relies on NFB for flat frequency response.
Wouldn't it be better to design a basic pentode SE KT66 (or 6L6) circuit that performs passably well, and then add the NFB to make it perform better?
Or is the drooping open loop frequency response intentional, and necessary for proper closed loop operation of the circuit?
--
PS - Tubelab SSE and SE use a triode first stage, not pentode.
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KT66 in tetrode (post 1) is not very linear, more than subtle correction is necessary.
Member Jane did it his way a couple of years ago:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Member Jane did it his way a couple of years ago:
An externally hosted image should be here but it was not working when we last tested it.
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