Capacitor on tone control - Printable Version
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Capacitor on tone control - Tucker - 09-07-2018
I’m recapping a Stromberg Carlson model 400h and I noticed that the wax/paper cap that connects the tone control to the chassis is rated at 1200 volts. It appears to be the original cap but the list of parts doesn’t show the voltage ratings. The other wax/paper caps are rated 600 volts or less.
Can this cap be replaced with a 1k rated ceramic disc or a 630 v yellow cap? I’m not sure why this cap would need to be rated for 1200 volts. Here’s the schematic,
http://www.nostalgiaair.org/PagesByModel/498/M0021498.pdf
RE: Capacitor on tone control - morzh - 09-07-2018
It needs not to be 1200V. C21, right? Can be the same as C20. Which I would say should be 450V and up. 600V is good.
1200V was probably what they had in stock.
Some radios use the tone ctl at the last stage paralleling the output xfmer driver; those caps could be exposed to spikes when the speaker is taken out, so they use 1200V rating; here it is not the case.
RE: Capacitor on tone control - Arran - 09-08-2018
It looks like what you have in this set is a combination power switch, and tone control switch, the capacitor in question appears to connect between the plate of the 6SQ7 tube and ground, basically it is switched in and out of circuit to cut the trebble. If it is an original part, and not a replacement, I have no explanation as to why a 1600 volt cap would be necessary, the highest potential that cap will see in that position is maybe 80 vdc. If it were a tone control with a potentiometer, and one end of it were connected to near full B+, and the wiper was connected through a cap to ground, then I could see a reason for a 1600 volt cap in that position since if it shorts out or becomes very leaky it can burn up the pot.
Regards
Arran