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37-670 capacitor questions - Printable Version

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37-670 capacitor questions - Tom Hamilton - 01-23-2014

Hi All,

I am slowly gathering information and parts to recap my 37-670 console. I've already ordered the schematic and service notes from Chuck Schwark and I'm following along with Joernone's restoration of a 37-2670 on You Tube.

I've got a bakelite block, 8035-DG that needs two 110 pf silver mica capacitors. That part I know. The part that concerns me is the working voltage, which, according to the Philco Service Bulletin No. 289 on Chuck Schwark's site, needs to be 1200 working volts. Is that still true? And, if so, where can I order them?

The other capacitor question concerns the two Philco original .0015 1500 volt capacitors that are item # 73 and 74 on the schematic. The schematic shows them each having a value of .003. Did Philco change them out for the ones I have? Should I try and find a couple of .0015 1500 capacitors or use something else?

Thanks a lot, Tom

RE: 37-670 capacitor questions - hsusmann - 01-23-2014

Hi,

Regarding the 1200 volt rating on those silver mica caps. That is just how they came back in those days. There is no voltage in your radio nearly that high so don't worry about finding a 1200 volt cap. The highest voltage you probably have might be 450 volts worst case. If you get something rated for 600 volts or so that will be fine.

Perhaps someone else has info on the 0.0015 uF values vs. the 0.003 uF for the other caps. Same thing would apply to those caps though in terms of voltage. Get something like 600 or 630 volts and you'll be fine.

Herb S.
Ithaca NY

RE: 37-670 capacitor questions - morzh - 01-23-2014

For mica caps - they are never exposed to this kind of voltage, and a typical mica cap today is 2-3 bucks for 630V rated cap.

Your #73 and 74 are a bit different. Many folks will say you do need over a 1000V rating.
In a normally working radio I do not see the reason for it, the maximum voltage is your B+ which is usually 270V or so.

However the effect know as "flashover" does exist in tube amps and is usually the result of plugging and especially unplugging the speaker while hot and playing. This creates very high voltages and the cap may get a breakdown. If your speaker is soldered in and not pluggable, there is no reason to expect it, and 500-600V rating would be just fine.

RE: 37-670 capacitor questions - Tom Hamilton - 01-23-2014

Hey,

Thanks for the quick replies.

I haven't received my service notes yet from Chuck. Hopefully, there may be something about a capacitor substitution in there. What I don't know is if my two .0015 capacitors are the answer or were the problem which was solved by changing the value to .003.

Tom

RE: 37-670 capacitor questions - morzh - 01-24-2014

The Rider lists the caps as 0.003uF. Unless you find factory ECOs to the opposite, go with the schematic recommended values.
The larger value could bring down the treble but perhaps this is what's required.

RE: 37-670 capacitor questions - Tom Hamilton - 01-24-2014

Thanks to all of you for the advice. I'll see if I can find any service notes regarding the .0015 to .003 change.

Tom

RE: 37-670 capacitor questions - OldRestorer - 01-25-2014

http://www.nostalgiaair.org/PagesByModel/222/M0013222.pdf

Always check nostalgiaair for schematics first. they are free

I always order what the schematic says. you can get the 1600v and the 1000v from just radios. they are on the right side of the order page about 1/2 way down

Kirk

RE: 37-670 capacitor questions - Tom Hamilton - 01-25-2014

Kirk,

Thanks for the information. I've already downloaded the Nostalgia Air schematic and service information. They're a bit difficult to read in places. I guess I've gotten somewhat spoiled using Chuck Schwark's schematic service.

Tom

RE: 37-670 capacitor questions - Warren - 01-25-2014

Yes, thats the problem with most the free schematics, hard to read. Sometimes cantr tell something important. I like Chucks schematics, plus you usually get alot more info on the radio.

RE: 37-670 capacitor questions - Raleigh - 01-27-2014

There are no DC voltages near 1200 volts in your radio, but there might be some AC spikes that run high enough to warrant that high working voltage. Caps on the plate of the output tubes, like your 73 and 74, are often high voltage caps for that reason.

I don't know where in the radio your 110 pf caps are unless they are 42 and 44, so I can't say why they need such a high WV.

Micas in the 3 dot package are all 500 V. In the 6 dot packages they can vary a lot. Default with no color in the voltage dot is 500 Volts. I recently saw a 100 volt mica in that package.

Check the change notices when you get the schematic from Chuck. That might tell you if Philco made a change in the value of 73 and 74 at some point.

RE: 37-670 capacitor questions - exray - 01-27-2014

On the 110pf caps they used a high voltage rating as a means of minimizing leakage. No need to do that with modern caps.

And yes, the caps on the audio output plates need to consider both the DC present plus any audio spikes. Best to go with 1000 or more.

RE: 37-670 capacitor questions - Tom Hamilton - 01-27-2014

Thank you all for all the advice. Whatever what value I decide to use on part 73 and 74, it will be very close to the voltage of the original caps.

Hopefully, Chucks schematic and service notes for my radio will be in today's mail.

Tom