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RE: 10uf isn't enough.

74.96.187.104

Lew

In Reply to: RE: 10uf isn't enough. posted by Ralph on February 15, 2024 at 09:17:09

What about the CCS? Would the CCS figure into the impedance seen at the plate of the CF, using the equation Z (looking down from the plate)= Rp+(mu+1)*Rk, where Rk is the very high Z of the CCS? In that case, 10uF bypass cap to ground would be overkill.

If I am wrong, then Z (for bypass calculation) = the parallel sum of 12K ohms and 2300 ohms (Rp for the ECC99). Then the net Z that needs to be bypassed for audio frequencies is around 2K ohms. In that case, I agree; 10uF is not quite enough. 50 or 100uF would be more like it.

At this point, it's all moot because I don't need to reduce plate voltage.

Follow Ups:

I forgot about that- it complicates things. - Ralph 11:09:00 02/15/24 (1)
A good CCS has a nice high impedance, so you're probably right.

Did you optimize the CCS to the operating point of the tube?

I've found it useful to run a sine wave thru things just to verify that the circuit is actually running the way its intended. More than once I've found it a country mile off.

Is this at the output of the MP-1 phono section?
- RE: I forgot about that- it complicates things. - Lew 12:21:43 02/15/24 (0)
  To your last question, yes.
  And yes I ran a sine wave through the circuit before finalizing. In fact I swept it from 20Hz to 10kHz.
  Now I think about it, I need to make a small correction in the calculation. The parallel sum of the 12K resistor and the net impedance from the plate down is essentially 12K ohms, because the tube plus CCS Z is so high. Still, 10uF should be enough.
  
  Edits: 02/15/24 02/15/24

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