The PHILCO Phorum
general question - Printable Version

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general question - DKinYORKpa - 03-16-2013

I have this set right now that had a bad output transformer and the only thing ever done to it was the replacement of the two 8 mfd filter caps. He used a 10 mfd for the rectifier side and a 60 mfd for the speaker side. Does the that 60 mfd and a bad OT go together? Did he just run out of 10 mfds? Thoughts? (every other cap is original and I can't wait to tear into this one, but that 60 is puzzling.) It's a Silvertone 1585 or Colonial 62)

RE: general question - Radioroslyn - 03-16-2013

No don't think so. If anything it would be a problem with the rectifier tube or the filter choke. What the power supply will see is a dead short till the 60uf cap starts to charge though the choke.
Terry

RE: general question - morzh - 03-16-2013

The dead short is only seen due to the 1st cap of 10uF, not the second of 60uF. The choke limits the current through the complex impedance, part of which is 2kOhms of active one.

But 60uF will not burn the output xfmr, and the only things that potentially could are: bad output tube 247 or the shorted speaker or a short in prime/second windings of the xfmrs itself.

RE: general question - DKinYORKpa - 03-16-2013

So he ran out of 10 mfds?Icon_biggrin

RE: general question - Arran - 03-16-2013

Sometimes output transformers fail for no apparent reason at all, although the one thing that could do it is the output tube drawing too much plate current perhaps. Many 1939-42 Philcos are notorious for having bad output transformers, they almost always develop an open primary. I don't believe that an output filter cap is to blame, I actually have a few Rogers built sets that use output filter caps of about that size, presumably it was because they were designed for 25 cycle operation.
Regards
Arran

RE: general question - morzh - 03-16-2013

Both my first two console radios, Philco 20 and Zenith 9S262 had output transformers' primaries open. Both got replaced with modern ones, a bit oversized for reliability.
I suspect I know the reason for the Philco - one tube in the output pushpull was gone, so badly it took 1.4k section of the multitap resistor with it. Although that might have been a consequence of the fried transformer. Which is not even important as long as it got fixed.

RE: general question - DKinYORKpa - 03-17-2013

The curious thing about the OT is that in the past, someone started to do something with it. When I removed the 2 bolt/nuts holding it on the speaker mount, the one side didn't separate, it was still riveted. I could then see that the other side was riveted, but the rivet was pried open. Thus the need for the bolt. So were the "guts" replaced in the past. None of this matters, of courseIcon_biggrin.