The AM Forum

I'm working on a Valiant and I noticed one of the series parallel combination caps (C39) was getting hot. While I'm replacing these I might as well replace that mica stack too. I've read the HT50 series doorknobs are good replacements, but they will end up costing more than the transmitter. Is there something cheaper that will hold up?

This was a problem for me also.Sent 2 sets of 500 volt micas up in smoke.Now have 1500 volt ones which are, so far, holding up. Thanks to Rodger,WQ9E was able to get a hold of caps to replace the other stacked caps.Perhaps he will chime in.I can send pix of what I did, if you like.............John

John, did you use regular 1500v silver micas or were they something different?
I was looking through Mouser and found these 1000v micas: http://www.cde.com/catalogs/CD-CDV16.pdf
Has anyone used these?

Those HT-50 size caps are fairly common at hamfests and Fleabay for a few SS each. The silver micas start to heat up on 80M and below as can be seen by the current chart listed so its best to spread the load with a couple in parallel. The various Heath SB family amps use a single 500pf / 2Kv silver mica and they do fail.

OTOH, the 100pf 7500V-12KV discs used by Ameritron and others up into the 2KW+ region seem to hold up very well; you might check Ameritrons price.

Carl

Chris,
         I replaced the caps with regular siver micas.Followed the Johnson manual as to 1/4 inch spacing between the series/parallel setup They were specific for a reason I would think.Believe I found the caps at Radio Daze. .....John

Thanks guys.

I think I will try some of those CDV16 micas in series parallel for the padding caps.