42-340 - Printable Version
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42-340 - joeinri - 12-28-2009
Hi everyone,
Looking for advice here. I've just re-capped a Philco 42-340. All seemed to be going easy...until I powered up. The radio was silent ...After a period of time,, > 3 minutes, the signal popped in and seemed great on all bands (2) good sound, and voltage measurement seemed fine. B+ is about 190V (180 on the schematic) I'm at a loss as to where to begin looking.
If I inject a tone at different points...I get it from front end all the way through. If's aligned good.
Any suggestions out there?
Joe
Re: 42-340 - Radioroslyn - 12-28-2009
Sounds like you may have a bad connection. Double check to see if all of the tubes are lit. Poke around when the set isn't working to see if you can find the trouble.
Terry
Re: 42-340 - joeinri - 12-28-2009
Thanks Terry!
I 'll do that, although I've been poking around for awhile now. All tube filaments are lit. All voltages look okay....just no signal getting through until it finally "pops" right in. I'm thinking along the lines of front end problems. Maybe in the antenna circuit. There are actually a few caps that I've not replaced. The "dominoes" in the Oscillator cirucit....haven't got correct values other than Ceramic type...and I don't think that that is the recommended replacements for these. I'll keep poking around....maybe touch that right connection that's causing my problems.
Joe
Re: 42-340 - Radioroslyn - 12-28-2009
If you think it's in the osc you can use another receiver to hear it. Set your Philco at 1000KC. Take another bc set and tune around 1460KC or so. Place the antenna wire near the osc tube. If the osc is running you will be able to a loud beat note (squeal) in the radio. If you move the dial on the Philco the note will change also.
Good luck
Terry
Re: 42-340 - exray - 12-31-2009
Sounds typical of an oscillator problem to me. My 42-327 acted the same way. I could wiggle or pull the tube and reinsert it and the oscillator would start working. I went thru several tubes and hosed the loktal socket to no end. Replaced everything in sight except for one very buried mica cap. Guess what the problem was?
Re: 42-340 - Raleigh - 01-03-2010
I had a similar-sounding problem with a Panasonic tube radio. The problem turned out to be an open grid bias resistor for the 50C5 audio amplifier tube. After warming up a few minutes it would start to work fine. If I turned it off and then back on, it would take another few minutes before it started working.
I measured the bias voltages and discovered it always worked fine with the voltmeter attached from the control grid pin of the tube to ground. Some bias current must have been getting through the meter, which clued me to check the resistor, which was open.
Your problem is likely something different, but the symptoms sound similar to my Panasonic.
Oh, yes, and I just remembered I had a similar problem in a Philco 41-280, which suddenly started taking minutes to warm up. It turned out to be the XXL oscillator tube. If I remember correctly I swapped the oscillator and mixer tubes (both XXLs) and the problem went away, but I may have replaced the oscillator with a spare.