Philco 38-3 hates me - Printable Version
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Philco 38-3 hates me - DuMont - 05-18-2020
This is something I've never encountered. I have my signal generator and frequency counter and output meter set up...and I can do the IF (470 at dial position 580) with no trouble.
When I move to begin the RF, the signal from the generator doesn't come through. All I get is an annoying buzz. (which, oddly enough, I can peak by turning RF adjustors)
Anyone have any ideas???
Thanks in advance!
RE: Philco 38-3 hates me - radiodale - 05-18-2020
Are you tuning the radio to the same frequency as the signal generator?
RE: Philco 38-3 hates me - DuMont - 05-18-2020
Yes. The alignment instructions for RF broadcast band are:
1600 on dial, 1600 on generator
580 on dial, 580 on generator (rock this adjustment)
1600 on dial, 1600 on generator
1500 on dial, 1500 on generator
RE: Philco 38-3 hates me - morzh - 05-18-2020
Check the input stage RF coils, check the input tube.
Wear a mask, maybe it won't recognize you.
RE: Philco 38-3 hates me - DuMont - 05-18-2020
Ha! Oh, this radio knows me by now! Coils are in good shape. Tomorrow I will set it up to begin RF alignment and will change out the following tubes, one at a time in the order written, and see if I get a signal back in from the generator instead of the buzz.
6A8G
6N7G
6K7G
While these tubes check out "OK" on my Sencor tester, I've sometimes seen "OK" tubes have something wrong with them that doesn't show up on the tube checker. Beyond that idea, I'm fresh out of ideas.
Who was that masked man????
RE: Philco 38-3 hates me - David - 05-19-2020
When set up a 580 try shorting across the blades of the tuner and see if it makes the same sounds as when you are tuning at the upper part of the AM band. I know it is a long shot but easy to try. Good Luck David
RE: Philco 38-3 hates me - DuMont - 05-19-2020
David, what would that tell me if it does make the same buzz?
RE: Philco 38-3 hates me - David - 05-19-2020
One or more blades (plates) are touching when you hit a certain point when tuning. The cause could be dirt or trash or a bent blade. David
RE: Philco 38-3 hates me - DuMont - 05-19-2020
Ah, ok. I'll check it. Thanks!
RE: Philco 38-3 hates me - DuMont - 05-19-2020
Tried that, nothing is bent or touching that I can see. Even gave it a shot of compressed canned air, but it's pretty clean.
RE: Philco 38-3 hates me - DuMont - 05-19-2020
Ok. I changed out these tubes, one at a time, and still got no signal back in from the generator in the RF alignment of 1600, 580, 1600 and 1500 instead of the buzz.
6A8G
6N7G
6K7G
HOWEVER: I did discover that the IF signal of 470kc does play up and down the dial. It begins to fade around 1200 on the dial, but is still present up to 1600. But, that does me little good since i can't perform the RF alignment getting nothing but a harsh buzz instead of a smooth signal tone. I can hear the occasional station, but it's scratchy and may as well be lost in space as far as where it's supposed to be on the dial.
RE: Philco 38-3 hates me - Tim Tress - 05-24-2020
It sounds like the oscillator isn't working. Try checking the components around the 6A8, especially the coils.
RE: Philco 38-3 hates me - RodB - 05-25-2020
I think you can check pin 5 of the 6A8 for a small negative voltage to see if the oscillator is running. If its not, with the power off and broadcast selected you can monitor pin 5 to ground with an ohmmeter and move the tuning condenser through it's full range. You should see a reading of about 33K with no movement in the meter. If the meter reads zero or moves off 33K the tuning condenser oscillator plates are shorting.
Rod
RE: Philco 38-3 hates me - captainclock1988 - 05-27-2020
What make and model of Signal Generator are you using?
The reason why I ask is because I haver 2 Signal Generators a 1948 Radio City Products Model 705A and a Heathkit Model SG-8 Signal Generator, and the Heathkit SG-8 Signal Generator would produce a tone on Band A but then on Bands B-E it would just produce a buzzing noise that would be able to be "peaked" but wouldn't be a definite tone, but then my Radio City Products unit would create a tone on all of the Signal Generator Bands and on all of the radio bands, so to me it sounds like it may be your signal generator rather than your radio.
Just my 2 cents. It might be worth checking into.
-Levi