Quote:
Originally Posted by Findm-Keepm
I too have had problems with mica caps - mostly Sangamo molded ones - they are "pinker" than most.
The brown Elmenco "drops" are all mylar-paper caps, vacuum impregnated just like the old Sprague Orange drops. I've used them in sets for years, depleting my many assortment kits (Arco/Elmenco sold the "brown drops" in service kits years ago) and most of my sub-.01uF 600V stock. Never a problem with any of them. I've got tons, thanks to friends that shut down TV shops over the years. They sell the test equipment, but give away the parts. 
I've had to quit using orange drops - the manufacturer (SBE) has shifted production to China. I found several new .0047uF Orange Drops that were leaky - several hundred microamps leakage at full voltage, giving me some freaky grid voltages in a Motorola radio I was working on for a guy at church. I think the shift to Rohs/lead-free or poor Chinese quality may be to blame. I've since shifted to Nichicon (XK series) and Illinois Capacitor (MSR/MPR) radials and axials. Much easier to obtain in small values, and cheap too.
There was an earlier thread talking about the Elmencos/maroon drops and problems, but nobody ever gave specifics. My Sencore LC102 and Sprague Tel-Ohmike both check caps at full voltage, so I've always relied on them for testing most caps. For quickie tests, I used to connect a 90V battery up to my VoltOhmyst with the cap in series to check for charge/discharge. Any residual voltage indicated leakage. I don't anymore - the dang battery went dead - ever price a new 214 battery these days? 
I'm gonna re-read your CTC7 saga!
Cheers, |
Thats why you build a 90V boost converter from a couple of 9V batteries. :-)
I did this to my old Eldorado/RCA portable tube radio. i created a 65V boost converter that ran off a single 9V, and then wrapped a couple turns of wire around the inductor, a diode and filter cap to get boost-derived filament battery supply. the 9V battery ran dead pretty quickly, but the circuit ran good otherwise, and so did the radio for the short time period :-) Same concept as the nixie tube power supplies, i basically used the same regulated nixie supply circuit. The only downfall to all of this, is you have to size your inductor, and i dont know the math. so i experimented. too small and the B+ wont reach required power and the inductor will overheat/saturate. Too large and it draws excessive current, and harder to regulate/overshoot.
What would be better is building the circuit inside a replica-style looking "battery", or a an old original but gutted battery and have a rechargeable lithium cell inside to run it. when it dies, remove the battery from radio and plug the charger into it.