[Jamie]

I've got a philco 620 that I can't get going. I'm still very new at repairing radios, so I am sure I've missed something. I do get a very low volume hum from the speaker, but you have to put your ear right next to it to hear it. It is not a tunable hum, nor is it affected by the volume control. If I touch the output lead from the tone control, I get some static. The field coil of the speaker gets very hot, but the speaker checks out fine with my multimeter. This radio had an accessory speaker tapped into the speaker wiring and I got no sound out of it either. It has now been removed, and the wiring restored to original.

I replaced all the caps, and checked the resistors. All of the tubes are good. That's about the extent of my abilities. I've got a feeling that I may have gotten one of the bakelite caps wrong, or missed a connection. If there is anyone near the Cincinnati or N. Ky area who would like to make some extra money, let me know. I really like this radio and I'm very disappointed that I've failed to repair it.

If anyone has any ideas, I need help. Thanks.

[marty]

Hi All;
I would suggest that the wiring arround and to the Field coil be checked, as it shouldn't get hot.. Check that the field coil is NOT shorted to the chassis..
It may have a short in the winding, but I would first check all of your wiring having to do with the Power Supply and from the Transformer to all the tapped out voltages, from the voltage dividing resistors..
Also check that all of your electrolytics are wired correctly, correct polarity..
Now, some of the other Guys and Gals with more experience may have other suggestions and say I am full of it.. but, it doesn't hurt to check your work, that much I know (from experience) for sure..
THANK YOU Marty

[Phlogiston]

Don't touch the lead from the tone control. The fact that you are not getting knocked on your butt suggests that the 243 volts that is supposed to be there is missing. The field coil on the speaker is getting hot because it is conducting too much current. Do not turn the radio back on less you risk burning up the field coil or the power transformer. Find the reason for the excessive current consumption.

[morzh]

The reason he is not getting knocked on his butt is probably because he is standing on an insulating surface, like a wooden floor or a carpet, and maybe not on the ground floor. And he is not touching the chassis with the other hand at the same time.

Still.....unless you are a pro or a very experienced person in elecrtricity, I would advise not to touch ANYTHING with your bare hands, even the chassis unless you are working off of an isolation transformer. Then you can touch anything. With one hand, keeping another one in your pocket.

[Jamie]

Thank you. thank you, thank you!!!!.

The field coil was shorted to the chassis where the hushatone was previously installed. That problem fixed, the coil no longer gets hot.
I had a bad solder joint to one of the electrolytic caps too. Problem fixed, the radio works now...

The tone control is bad though. I am getting sound now, and can tune stations, but only when the tone control is in the open position. I was touching the lead earlier, but one hand in pocket, standing on carpet, using a plastic tool. I am sorry.. it was stupid.

Thank you guys for putting me on the right track. I was giving up. FYI - your answers matched the 1943 edition of Radio Troubleshooters Handbook. You guys are good! ...

Now the question is, what is the value of the tone control? the Philco part number is 30-4316... Can I just solder a cap across the leads, or do I need to find a new tone control?

[Phlogiston]

No problem. I would rather your radio not work, than you (not work).

Some of those tone controls used 2 caps - 2 positions - or just one. Something like a .02 at 630 volts will not make it too muffled with the tone "on". On the schematic it looks like it goes through 2 of them to ground. A little unusual. See if your tone control grounds one end of that cap.

[Jamie]

I looked at the schematic and it looks like it's .02mf. I took the old cap out of the tone control box and it is a single unit. The strange thing is, it is a three position switch. So I soldered a new .02 cap in place, and now it only works in the other position. Just the opposite from before. When it's open, there is no sound.

Here is a link to the schematic.. tone control is number 60
http://www.nostalgiaair.org/PagesByModel...013804.pdf

The only other issue is that the volume is about 1/2 what it should be.

Any ideas?

[Phlogiston]

When "its open" it might be shorted.

Have you checked the voltage on the plate of the 42? When you turn the tone cont. it should not change (much). If you do not have the 240 V, turn it off and look for another problem.

Have you done a recap and component check on the radio?

[Jamie]

No, I have not checked the plate voltage of the 42. I will do that tomorrow morning. Yes, I have done a total recap and component check (resistors). A weird thing about this radio was that all but one of the tubes were dead when I got it. The bad ones have been replaced.

Someone did some shoddy repair work a long time ago, as an old paper cap was wired right across one of the cans.. I mean - someone just jumpered one of the 8mf connections by soldering a new cap, while leaving the old one hooked up. That paper cap was totally melted. And the brush hushatone attachment was not even soldered in, they just spliced the wires and taped it up.

I've been working on this radio all day. I need some rest. I'll check in tomorrow. Thank you for your help.

[Jamie]

I finally got time to work on the 620 this morning. I put all new wires to the tone control, and also replaced all the speaker wires. The radio only works with the tone control in one position. If I switch to the open or .003mf circuit, I get nothing. Plate voltage for the 42 tube is 10 volts (if I am using the correct method to check it). When the radio is working, volume is about 1/2 of what it should be. The 42 tube tests very strong. Something is very wrong. Any ideas?

[Phlogiston]

Take the tone cont. out of the circuit and test again. The plate of the 42 should be around 240 volts. If that voltage is being taken to ground it could be very bad for the OP transformer and/or the power supply. So test right after warm-up and carefully.

What are you using to measure voltage? Can you measure all of the pins on the 42 for DC volts except the filament(s) contacts?

[Jamie]

Ok, I've been working on it. This is going to be difficult for me to describe because I may not know the correct terminology in order to explain to you exactly what I've found.... but here goes..

This radio has had previous work done on it, so, assuming the mistake lies in the previous work, I started tracing things according to the schematic. I noticed that there is a connection between one of the 8mf electrolytics and part number 33-3222 (70 on the schematic), (also, this is correct according to the schematic)... well, a wire had been added that connected the ground end of the same 8mf cap to the same joint on 33-3222. To me, that represents a short! .. So, I removed that wire and voila! I have full volume and the tone control now works on all three settings.

The only problem now, is that there is a hum all the way across the dial. It isn't terribly bad, it almost sounds like interference.. but it isn't right. Any ideas?

[Arran]

The way that the stock tone controls are built is that they typically have one or more potted capacitors mounted in a can on the back side, they may account for the odd behavior on the volume level if you missed those or if someone messed with the wiring.
Regards
Arran

[Jamie]

Thanks Arran. I replaced the cap in the tone control and it appears to be working fine. The tone control works on all three settings now. The only remaining problem is hum. The radio hums all the way across the band. It's not terribly bad, but it is annoying. The hum increases if you increase the volume. Other than the hum, the set actually works well now. It pulls in some distant stations too. I've replaced all the caps, and I've checked and replaced resistors too. There is also some distortion and garbling above 70% volume level. I'm trying to trace everything according to the schematic, but it's very difficult.

Phlogiston, thank you. As soon as I removed the wire, plate voltage on 42 came up to 245. I'm using a DMM to measure. I'll check the other voltages too and report back.

This radio must've been fairly new when someone attempted to repair it. The bad wire I found was almost identical to the original cloth wiring. I only found it because, when I first looked at the chassis, there was a huge, melted paper cap in that area. It was not original. Then I noticed a huge glob of solder connecting this wire to part 33-3222. I'd originally attributed the solder glob to the melted cap, but the wire had been added too. Perhaps this repairman was trying to fix the same hum I am experiencing?

Any ideas where this problem could originate from? If I could narrow down the hunt, it would be a great help. Thanks.

[marty]

Hi All;
One possibility, but not the only source of Hum.. Is if the Power Transformer circuit, is not filtering good enough, or is wired wrong.. Possibly, too low of a Capasitance, in the circuit, bad choke or not wired in, when subbing resistors for choke the Capasitance is not big enough to overcome the resulting waves in the AC turned to DC..
My Philco 34 power supply for the 137 Volt supply had too low of a capacitor to do its job and so I had lots of hum.. I ordered some new ones in ( got them in yesterday ) and it took care of my Hum problem..
THANK YOU Marty