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In Reply to: RE: The example fails minimum inductance requirements posted by hennfarm on June 09, 2016 at 10:50:31
I have been considering 211 push pull instead of se with hf filaments it wouldn't be a expensive amp to build and run. I am not sure how long the tubes last. I run my main amp 18 hours a day so running costs add up for me. Any one that has posted about a 211 push pull amp over the years(and it seems not many people do) has been positive about them.
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Perhaps a Ccore would be the best option to get anywhere near enough inductance. I am thinking 160H would enough So halved across the transformer (is that what happens approximately?) that would work out in the ballpark of 80H which is what the best 211 trans have that I have been shopping around for. 211 is not the only tube I want to try but it is the highest plate resistance of the tubes I want to try. The ones that are higher I want to use in A2. Would 160H put in back into the possibility of fitting into the window of a affordable EI core like one done by heyboer?
From the Lundahl datasheet,
"We define Power Low Frequency Limit, FPL
, as the frequency where LP= R LOAD. (The reactive impedance of
the transformer equals the primary load impedance). At FPL, the output power is reduced to 50%"
I don't think that's right.
If you had a 10k single ended transformer with 80Hy of inductance and you were driving it with a 10k source then at 20Hz (where the reactance of the 80Hy is 10k) the power would be 50%. (10k//10k=5k)
But the 3300 ohm plate resistance of the 211 (for instance) would swamp that equation. So that aside,
What the 10k reactance of the 80Hy of inductance in parallel with the 10k reflected impedance will do is cause an elliptical load line.
With 160Hy the reactance would be 20k at 20Hz so 10k//20k=6.667k and that will still cause an elliptical load line.
And that elliptical load line won't just be for 20Hz.
When low frequencies are present, all the frequencies will be following that elliptical load line and elliptical load lines increase distortion.
TK's 5X or 10X rule would prevent a elliptical load line but I don't see how it can be obtained in a gapped transformer (or plate choke).
Parafeed, using a CCS for the plate load, would work (parafeed output transformer don't have air gaps and have plenty of inductance) but if a plate choke or series feed SE output transformer is used.....using them to play bass seems out of the question.
P.S. I know I didn't answer your question. I don't know how much inductance can be had without causing other problems. Whatever the answer is, I don't think it's enough.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Plan B LL9202 I have posted above a question about the LL920 am verses the silicon core. I am leaning towards going that route first. Probably a higher chance of success.Then I can give up on the parallel feed 211 and have wound a smaller choke for the a2 tubes.
Edits: 06/10/16
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