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In Reply to: RE: Dynaco SCA-35 question posted by gkargreen on December 26, 2016 at 18:13:47
See the schematic in the link. Looks like C18, 250V rated 1 uF. Use a decent film cap. A solens or something like that.....
Follow Ups:
Thanks, this schematic does have the proper value for C18 which you noted as 1 mfd @ 250 vdc, my schematic did not have that value, so unless there are multiple versions of the SCA-35... I have several 1 mfd @ 160vdc I would use IF the voltage across C18 is around 100 vdc or less, that is what I was hoping to learn. I see that C18 is across the cathode to screen grid of the 7199, so it could be higher than 100 vdc, time to ask Dave!
Hi
If you can believe the voltage chart in that same document then pin 3 of the 7199 is 32 volts. The cathode is listed at .7 volts as far as I can tell from the bad copy. Makes sense since it ties to the 16 ohm tap and ground through that cathode resistor. So my guess is that even as the tubes are warming up, the screen of the 7199 will never see over 100 volts. You could always tack a cap on there and fire it up and watch. Even a 100V cap could take that turn on surge the first time. My guess is it never anywhere near the 160V rating of the caps you have on hand.
Thanks, dls, that is an excellent suggestion!
Yes, the plate of that section is listed at 55 volts. Even at warmup before the tubes draw the supply down I bet that plate never goes over 100-120 volts. The screen will be below that, and the cathode will be around ground... No way that cap sees over 100-120 volts at turn on if that schematic is correct. Of course it sees 30-40 volts tops at steady state.
Excellent, thanks so much!
Let's just hope the schematic is correct! It should be, it is the Dynaco original kit instructions....
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