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RE: Frequency, etc

208.86.125.199

In Reply to: RE: Frequency, etc posted by Lew on March 23, 2021 at 13:14:12

You could try a soft recovery diode, but I would be inclined to focus on the RC time constant, trying different values for C202 and C204 or the varistor RV201 and RV202. Regarding R201/R203, I had missed that. That is a good question why one is 10K the other 22K. I agree with you, I would experiment with changing those. I would guess that it was simply a mistake on the schematic, someone meant to change them both to the same value, and only one was changed. But geez I have seen stranger things.

Follow Ups:

RE: Frequency, etc - Lew 15:48:05 03/23/21 (2)
As you say, I have been assuming that the value shown for R201 (10K) was in error on the schematic. Especially since on both of my actual amplifiers, R201 = R203 = 22K, with the attendant C202 = C204 = 470pF. On the 1977 schematic, C202 and C204 are 290pF. So they were clearly tinkering with that part of the circuit.

1977: uses 47K and 290pF, both sides
1978: uses 22K and 470pF, both sides (assuming 1978 schematic is in error)
- RE: Frequency, etc - fredtr 17:40:23 03/23/21 (1)
  It looks like the other thing they changed were resistors 206 - 210, which will affect amplifier loading and the feedback path. Are these resistors 1.0M or 2.2M in your amplifiers? Have you experimented with different values for these resistors?
  - RE: Frequency, etc - Lew 18:59:16 03/23/21 (0)
    2.2M in all positions. Still, I got crazy and replaced 4 out of 6 on the oscillating amplifier, to no avail.

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