Philco 97B: Restoration by a college student
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Hey, guys. I'm new here, so pardon my ignorance. I'm taking an Audio & Recording class at Harding University, and we have a "creative project" due by the end of the semester. My father and I worked on vintage tube equipment a lot when I was younger, and I know my way around a schematic, soldering, troubleshooting, etc, so I planned on restoring some sort of tube equipment and documenting it for the project (which was approved). I was able to acquire a 1935 Philco 97B radio for free. I have never worked on something this old...so I'm hesitant to start working on it. The person who handed it off to me demonstrated that there is a slight buzz when plugged in. Not loud, but there. No stations tuned in. The light changed as the band selector changed. Any advice on getting the ball rolling on this? Like I said, this isn't my first radio, just the first in a long time...and definitely the oldest. Thanks!
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Welcome.
97B is a beautiful tombstone radio.
http://www.nostalgiaair.org/Resources/903/M0013903.htm
This is the sch and some guidance. Alignment, BOM etc.
If want a better quality sch, ask Chuck Schwark here or at Philcorepairbench.com.
Tubes work at high voltages do be careful.
Also, do not plug it in (whoever did it was wrong - bad idea) before you recap it.
Start with recap.
One good thing that came out of plugging it in is - you know power is working and the speaker too.
Replace all capacitors except mica type. Electrolytics, tubular and backelite tub types.
Then proceed.
Best
Mike
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
(This post was last modified: 02-12-2017, 01:37 PM by morzh.)
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You do not want to remove and discard the original bakelite plastic cased caps. Rather you can remove the innards and install modern film caps inside. This retains the original appearance and they also serve as terminal tie points for the other wiring.
Do a search on this site and you can find detailed info on how to accomplish the rebuilding of the bakelite caps.
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mafiamen2
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Welcome DSmith, I would also replace the resistors in the radio. You could unsolder each one and take it out of the circuit to test it, but I don't bother. Resistors are probably the most inexpensive parts in the set, and if you have it out to test it you're halfway to replacing it anyway. The older resistors, if you test a few, have probably drifted out of spec anyway. I personally prefer the peace of mind of new components in the chassis, especially when they only cost a few cents each usually. Take care, Gary
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Gary - Westland Michigan
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I say only replace resistors if totally whacked, and if there are tubular caps - replace not restuff.
Backelites - if not willing to restuff, drill the thin wires out of the eyelets and use the lugs as mounting points for new caps.
I only suggest this as Dsmith as a student and might have a deadline to meet plus other obligations.
This is why I wouldn't goad him towards authentic looks - the functional repair will suffice.
Unless of course he has the time and the desire, then sure.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
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Welcome to the Phorum!
As you can see, lots of help here. Post pics of questions and progress, it will help at final report time.
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Happy happy Trails ,,,CHEERS
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With regard to the resistors, with few exceptions, you should be able to test them in place. The exceptions would be if the resistor was connected in parallel with a coil or a transformer, since those are often of a lower resistance then the resistor. One resistor to pay close attention to is a pair of wire wound resistors on one form, listed as part number #58 on the schematic, one or both sections can become open circuit. With regard to replacement resistors make sure that you get replacements of a high enough Voltage and Wattage rating, in some cases it doesn't matter like for a grid or cathode resistor, but watch out on the plate load resistors if the voltage is above 250-300 VDC or so.
Fortunately since this is a seven tube set there are not as many paper capacitors to deal with as a larger model, so restuffing the Bakelite blocks or even any cardboard tube types would not be that time consuming. Morzh (Mike) has a fairly efficient method that is permanently posted in the tech section on here.
Regards
Arran
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