Philco 20 volume control problem - Printable Version
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Philco 20 volume control problem - Tubesforme - 02-01-2017
I restored a Philco Model 21, which has a late Model 20 chassis. The original volume control was badly rusted and wouldn't turn. I obtained a replacement that was the very same make and style as the original and it tested good and turned freely. I opened the back and cleaned it with DeoxIT D5, before installing it. The radio played great and continued to do so for a number of weeks. then it began acting like a noisy volume control does. I took the chassis out of the cabinet and cleaned it again. Same thing happened again. This time it played great for a couple of months. Cleaning the control returned the radio to normal, but I have never had anything like this happen to any other radio I have restored and the problem is happening again. All parts and tubes test good. It is only the control gets noisy. Has anyone else had any experiences like this? If so what was the solution? Thanks guys.
RE: Philco 20 volume control problem - Tubesforme - 02-01-2017
I just had this radio out and cleaned the control. It played on the bench for three hours, no problems. I reinstalled it in the cabinet and continued to play it. While the volume control is working normally, I have noticed that randomly the volume will drop slightly. If you leave the radio alone it will suddenly come back up. If you raise the volume with the control, when it drops, when it comes back it is way too loud for comfort. I have monitored the output tube bias on the 71's and that stays constant so it isn't a problem with the transformer. I am not able to get to the 27, first audio to monitor any voltages. I have substituted all of the 24's and the 27 with known good tubes and that isn't helping. Thanks guys.
RE: Philco 20 volume control problem - KCMike - 02-01-2017
Just an idea if you haven't tried yet. Poke around the under chassis with wood dowel or something similar when problem occurs. Might have a bad solder joint somewhere.
RE: Philco 20 volume control problem - Tubesforme - 02-02-2017
(02-01-2017, 08:12 PM)KCMike Wrote: Just an idea if you haven't tried yet. Poke around the under chassis with wood dowel or something similar when problem occurs. Might have a bad solder joint somewhere.
Been there, done that! In fact I have resoldered all of the chassis grounds and all of the capacitor blocks that I rebuilt. I have the chassis out of the cabinet and not a single voltage varies, on anything when I probe and pull on the connections. I have even tightened up the tube socket contacts and hand cleaned them.
This doesn't happen when I have my signal tracer connected to the chassis so am thinking I need the chassis ground and being this is a TRF set, need a longer aerial. I noticed the position and direction of the 20' wire I am using does make major changes. A problem is in Los Angeles, we have far too many stations and they will leak over one another on a TRF chassis. My model 70 works just fine.
None of this, however, explains why the volume control seems to get noisy so quickly.
Thanks
RE: Philco 20 volume control problem - Radioroslyn - 02-02-2017
A rotting rf coil anyone??
Have checked the resistance of your pot before you clean it??
Check the rivet that holds the ant fastenstock clip, could be a bad connection there.
RE: Philco 20 volume control problem - GarySP - 02-03-2017
I agree with Radioroslyn. Might have an iffy RF coil. Fortunate that they are not to hard to remove from the chassis and rewind. Actually one of the easier coils to rebuild. Check the ground clip on the chassis as well. The one on my 20 was loose. I drilled out the rivet, sanded the contact points on the clip and chassis, and reinstalled using a stainless steel rivet. Take care, Gary
RE: Philco 20 volume control problem - Tubesforme - 02-03-2017
(02-02-2017, 11:18 PM)Radioroslyn Wrote: A rotting rf coil anyone??
Have checked the resistance of your pot before you clean it??
Check the rivet that holds the ant fastenstock clip, could be a bad connection there.
Yes, the original coil was open and was replaced when the chassis was restored. It was tested again and is good. The pot resistance was tested, out of circuit and it is perfect. I tested it with a VTVM, not my DMM. The antenna connection rivet was replaced with a screw.
RE: Philco 20 volume control problem - Tubesforme - 02-03-2017
(02-03-2017, 12:17 PM)GarySP Wrote: I agree with Radioroslyn. Might have an iffy RF coil. Fortunate that they are not to hard to remove from the chassis and rewind. Actually one of the easier coils to rebuild. Check the ground clip on the chassis as well. The one on my 20 was loose. I drilled out the rivet, sanded the contact points on the clip and chassis, and reinstalled using a stainless steel rivet. Take care, Gary
I did replace the fanstock clip because the original was totally destroyed. I do not have the chassis connected to any ground because I live in a large apartment building. I am afraid to try and connect the chassis to the electrical ground.
RE: Philco 20 volume control problem - Radioroslyn - 02-03-2017
original coil was open and was replaced
Did the replacement have a rewound primary? If not could be it's starting to give up the ghost too.
A crummy ground is better than none. As it stands with out a ground it's getting it ground though the neutral side of the ac line via the line bypass caps. Try grounding it to the outlet and see if that helps. It's should make the vc work better (more control). It may not do anything about the signal level going up and down while the vc is stationary.
RE: Philco 20 volume control problem - morzh - 02-03-2017
OK. It is "Fahnestock".
RE: Philco 20 volume control problem - Tubesforme - 02-04-2017
(02-03-2017, 09:39 PM)Radioroslyn Wrote: original coil was open and was replaced
Did the replacement have a rewound primary? If not could be it's starting to give up the ghost too.
A crummy ground is better than none. As it stands with out a ground it's getting it ground though the neutral side of the ac line via the line bypass caps. Try grounding it to the outlet and see if that helps. It's should make the vc work better (more control). It may not do anything about the signal level going up and down while the vc is stationary.
The replacement transformer was an original and not rewound. By the way I tried using my signal tracer to see where the problem might be. the problem is I live in Los Angeles and using the diode RF probe, on the tracer brings several strong stations, mixed, in together. When I disconnected the detector cap and connected it to the tracer, I had a good signal, however I didn't dare use much volume or it would distort. That is when I discovered that with just the signal generator ground connected to the chassis, the radio volume was better. The model 20 does not use AC line bypass capacitors. I also noted that the dial alignment is way off. I just ordered an alignment tool and will try grounding the chassis as well as aligning the chassis per the instructions that Ron Ramirez posted.
Just wanted to thank everyone for your suggestions. The problem was proper alignment and a ground as well as a longer aerial. I hope this also fixes the problem of the volume control acting like a noisy control after the cleaner has completely dried out. It just might be the ground that corrects that problem because the control is WW and one side goes to the chassis ground.