Philco 38-12 - Printable Version
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Re: Philco 38-12 - radiola - 05-06-2011
This set was original when I got it. I changed the capacitors and checked the resistors for -20%. It played well but made a popping noise about every 10 seconds. Then nothing. I took it apart again and found the oscillator coil to be rotted, in order as stated above. That's when I got a new oscillator and the real fun started. I will try what you have written above asap. Thanks for the response!!
Re: Philco 38-12 - radiola - 05-07-2011
Hi Terry, I did what you said, step by step, but the problem I had was squealing and even occasional motorboating. I guess if it won't put out a good signal at the grid cap with a signal generator, there is a big problem. Actually the set is getting worse. Last week I could get a clear signal at the grid cap. This one's got me backed into the corner. Even the speaker sounds compromised having to put up with all that high decibel noise. If you have any more ideas, I'm listening. I'd hate to loose this one. Thank you. I'm adding those instructions to my repair folder.
Re: Philco 38-12 - Radioroslyn - 05-07-2011
Ok well then adj for max signal before it starts to oscillates. You could try bypassing the B+ with a .1@600v at the point that the B+ goes to the IF transformers. That may stop the oscillation.
Terry
Re: Philco 38-12 - radiola - 05-09-2011
Terry, thanks. I think I found the holdup. There was gunk on the padders--underneath the first I.F. transformer can. I loosened the screws and dropped some 3 in one oil between them, let it loosen, then sprayed it with tuner cleaner to clean them out. I will also clean the 2nd I.F. transformer padders underneath. Then, I should be ready to align. Thanks for all your help. I've printed it all out for next time I have alignment problems. MUCH appreciated!!!
Re: Philco 38-12 - radiola - 05-15-2011
May 15th-All did go well. The oscillator coil works well now. I had to take the I.F. Can apart and clean out around the padders. They were clogged, which kept me form making the needed adjustments for the new oscillator. Thanks for your assistance!! Much appreciated!!!
Re: Philco 38-12 - radiola - 05-18-2011
Now it's time to move on to the last stage of this saga, which is the replacement of the speaker. I will probably have to recone this one in the future, but for now, I want to replace it with a compatible one. This is a strange setup. The field coil is on top of the speaker, but where is the output transformer?? What are the steps I need to take to replace the speaker in this particular model? Thanks in advance.!!!!
https://picasaweb.google.com/lh/photo/IiVDf_G-WiM9ScLA-FpdvQ?feat=directlink
Re: Philco 38-12 - Radioroslyn - 05-18-2011
Your pic doesn't show the speaker, just the bottom. The thing on top of the speaker is the output transformer. The field coil is at the back of the speaker where the magnet would be on a PM speaker.
Terry
Re: Philco 38-12 - radiola - 05-18-2011
Okay, that answers my question. My new speaker just got here since my earlier post. It is a permanent magnet speaker with an output transformer on top, so I plan to replace the field coil with a 10 w resistor and use original output transformer. If there is a humming, I may have to go higher on the first electrolytic cap. Sound good?
Re: Philco 38-12 - Radioroslyn - 05-18-2011
That will work.
Terry
Re: Philco 38-12 - radiola - 05-19-2011
Okay, removing the electromagnetic speaker and replacing it with a pm speaker. For field coil, I used a 1500 ohm-10 watt resistor. New speaker hums. Replaced 12 mfd power cap with a 16--less hum but still bad. Replaced the 16 mfd with 20 mfd. Less hum still, but unacceptable hum level still. What should I try next. Thanks for your comments!!!
Re: Philco 38-12 - Radioroslyn - 05-20-2011
Two things you can do replace the two filters with 47mfd caps or replace the resistor with the primary of an audio output transformer.
Terry
Re: Philco 38-12 - radiola - 05-20-2011
Are you saying to use an extra output transformer as a field coil?
Re: Philco 38-12 - Radioroslyn - 05-20-2011
Yup. Or even the primary of a small filament transformer. Just want to put a bit of inductance in the power supply. It works so much better than a resistor. The more inductance the less capacitance you'll need to get rid of the 60cy hum.
Terry
Re: Philco 38-12 - radiola - 05-20-2011
Thanks, Terry. As soon as I get a chance, I'll do that and let you know how it turns out. Much appreciated.
Re: Philco 38-12 - Radioroslyn - 05-20-2011
Just a small note. The speaker with a field coil is called an electrodynamic or dynamic speaker. One with a magnet on the back is called a pm speaker or permanent magnet speaker. Just so we are using all the proper terms, makes everything easier to understand.
Terry