Philco 38-3 completely redone no reception - Printable Version
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Philco 38-3 completely redone no reception - DuMont - 04-06-2020
Hi, All -
I've finished a COMPLETE recap and all new resistors in a 38-3. The magnetic tuning switch works, and when the dial handle is pressed down to turn the station rotator, the volume drops accordingly. The only problem is - the volume is nothing but static. The set volume control will increase or decrease the sound. All tubes check out fine on a Sencor tester. Here's the strange thing - it was actually receiving stations before, and worked fine. This was after my total recap and resistors. I have it in a rack I built that I can either have it rightside up or upside down (to work on the chassis innards). Is it possible that when it was moved back to an upside down position something came loose in an IF can? I have a single longwise antenna connectd to the RED position, the other two positions are jumpered together. I have gone through it with a fine tooth comb looking for possible shorts and wire touches, see nothing. It turns on fine, it warms up fine, and all it gives me is static. I'm going to use my meter to check continuity on the coils later today, but under close physical examination I see nothing wrong there, either. I'm at my wit's end on this one....
RE: Philco 38-33 completely redone no reception - Radioroslyn - 04-06-2020
38-33 is a battery set.....
RE: Philco 38-33 completely redone no reception - DuMont - 04-06-2020
Sorry! It's a 38-3 Code 121. Floor console. I've got two laptops going here as I work from home!
RE: Philco 38-33 completely redone no reception - John Bartley - 04-06-2020
Turning a radio on it's side or upside down will not create a defect where there was none before. If there was a solder ball, splatter etc that came loose that's a different story. You can always turn it over again and shake it gently to see if anything dislodges.
Otherwise, following your schematic, probe your way from the speaker back to the antenna with a signal generator and see where the signal stops.
If no test equipment, go back over your repairs, one at a time and check them off on a print out of the schematic.
Testing voltages is also a good troubleshooting step..
To avoid creating extra troubles, do no more changes. You have enough to check out now.
RE: Philco 38-33 completely redone no reception - DuMont - 04-06-2020
Hi, John -
Thanks! As soon as I'm done for the day I'll get back to it and see what happens when I follow the trail.
LOL - there are no more things to be done with it - except finding out why it's got static and no signal!
RE: Philco 38-33 completely redone no reception - Radioroslyn - 04-06-2020
No problem but just want to be sure which model we're talking abt.
Agree w/ John would start w/ a generator @ 470kc 400cy modulation and connect it to the grid cap of the 6A8. If the IF stage is working you should be able to hear the generator very well. While you have it connected you can adjust the IF transformer for max signal.
GL.
RE: Philco 38-33 completely redone no reception - DuMont - 04-06-2020
Thank you, Radioroslyn. I have a BK Precision generator and will give that a shot. In my real life I do the media relations for the Alzheimer's Association in Texas, so the Philco project has been a nice unwind for me. Before I use the signal generator, should I go ahead and run continuity tests on the coils with the Fluke?
RE: Philco 38-33 completely redone no reception - RodB - 04-06-2020
I had a similar problem with a radio I had recapped. It turned out to be one of the tuning cap connector terminals below was bent just enough to touch the chassis. I had to bend it when I unsoldered the connection.
RE: Philco 38-33 completely redone no reception - DuMont - 04-06-2020
Thank you RodB!
I've looked at that tuning capacitor until I'm cross eyed, but again, who knows? I will give it another look with a really BRIGHT light on it.
RE: Philco 38-33 completely redone no reception - Radioroslyn - 04-06-2020
Another check for the tuning cap is measure the resistance from stator to rotor. For the most part it's going to be very low in some instances an ohm or so. Check with the plates open and closed. If it drops when it's closed you may have a bent plate causing a short.
RE: Philco 38-33 completely redone no reception - DuMont - 04-06-2020
Radioroslyn, THAT is a terrific trick to try! Thanks! My dad worked for IBM for many years, he would have loved hanging out on this chat board!
RE: Philco 38-33 completely redone no reception - DuMont - 04-08-2020
Hi, guys
Managed to grab a few minutes last night to check continuity on all the coils on the 38-3, and there are no broken wires.
Out of curiousity, I touched one probe to the chassis and the other probe to the antenna terminal marked RED. That's where I have my longwire antenna attached. The other two terminals on that piece of fibre board are marked BLACK and GND, and are jumpered together and grounded to chassis. I recorded continuity between the RED terminal and the chassis. Should that happen? Thanks!
RE: Philco 38-33 completely redone no reception - DuMont - 04-09-2020
Checked my 1946 Philco on the same continuity thought about antenna, and it did the same thing - so obviously that's not the problem. Tonight I'll flip it over and shake gently to see if anything tumbles out, then go to work on checking out the rotors and stator for a short.
RE: Philco 38-3 completely redone no reception - morzh - 04-09-2020
If your antenna loaded to the RF transformer to chassis, this is what you should see.
RE: Philco 38-33 completely redone no reception - DuMont - 04-10-2020
Nothing fell out, rotors/stators are insulated from each other. I used a generator @ 470kc 400cy modulation and connected it to the grid cap of the 6A8, but got nothing but a loud buzz.