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philco 37-630
murf
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#1

11-08-2013, 07:05 PM
Have been working on a 37-630 console that I picked up.
Someone has replaced the electrolitics recently.
No audio when I got it.
Found the output tranny on the speaker to be bad.
Bought a replacement speaker with tranny on ebay.
That took care of the audio problem, but it is distorted at lower volume. sounds better at higher volume.
Seems to get more distortion as it warms up for a while.
Have replaced a bunch of caps and a few resistors, checked the tubes.
Any chance the tranny on the new speaker is ok, but the voice coil is weak
Have not replaced any of the caps in the bakelight blocks yet.
I know some of the tubes checked barely in the green zone.
Which tube would have this effect on the am band?
Thanks and hope you guy's have a great weekend.
murf
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BrendaAnnD
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#2

11-08-2013, 07:16 PM
Restuff those bakelite caps. You'll find your problem goes away. The coupling cap for the audio is in one of them. What's going on is most likely that coupling cap is leaky and allowing DC on the grid of the output tube.
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morzh
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#3

11-08-2013, 07:32 PM
Murf


One would think long life in this forum should teach you one thing at least - do not leave old 70-year old caps in your radio. Why wait?
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codefox1
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#4

11-08-2013, 08:08 PM
Aye. Recap, Recarb, and then report. Always happy to help.
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AI2V
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#5

11-09-2013, 12:21 PM
The first place I would look is the grid voltage of the audio output tubes. I haven't got a schematic handy but I would hope to see something in the range of -10v to -16v.
Pete AI2V
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Phlogiston
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#6

11-09-2013, 02:52 PM
And don't run it anymore or you might be looking for another OP transformer.
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