1935 GE Model A-53 AM/SW Tombstone Radio

[vortalexfan]

Well for sure something's not right with this radio because the back of the radio says it's rated for 65 watts at 120 and the radio as it sits with its incessant 60 Hz hum is only 43 Watts so something's not right, either one of my filter caps failed or there's a bad tube or something else odd is going on with this radio.

I've tested all of the tubes in this radio and the 6K7 tube and the 6F6 tube both tested as having a H-K Short in it so I subbed them out with known good tubes and the hum is still there and the radio pulled the same amount of wattage, So I'm not sure what's going on with this mystery of a radio.

I'm about tempted to just salvage the bulb and tubes and capacitors out of the radio and scrap it out.

[dieseljeep]

Originally Posted by vortalexfan

Well for sure something's not right with this radio because the back of the radio says it's rated for 65 watts at 120 and the radio as it sits with its incessant 60 Hz hum is only 43 Watts so something's not right, either one of my filter caps failed or there's a bad tube or something else odd is going on with this radio.

I've tested all of the tubes in this radio and the 6K7 tube and the 6F6 tube both tested as having a H-K Short in it so I subbed them out with known good tubes and the hum is still there and the radio pulled the same amount of wattage, So I'm not sure what's going on with this mystery of a radio.

I'm about tempted to just salvage the bulb and tubes and capacitors out of the radio and scrap it out.

It depends what condition the cabinet is in! If the cabinet is in good condition, it's worth trouble-shooting a little further!
Remove all the tubes but the 6F6 and the rectifier and see if it still hums, proving it's a power supply issue. If so, bridge the electrolytics and see if it clears the hum. The power supply is a rather simple supply using a grounded B minus.

[vortalexfan]

Originally Posted by dieseljeep

It depends what condition the cabinet is in! If the cabinet is in good condition, it's worth trouble-shooting a little further!
Remove all the tubes but the 6F6 and the rectifier and see if it still hums, proving it's a power supply issue. If so, bridge the electrolytics and see if it clears the hum. The power supply is a rather simple supply using a grounded B minus.

The Cabinet is actually in pretty decent shape yet, but I did try what you suggested last night before I even saw that you suggested it, and it still has a hum, actually the hum got worse when all but the 6F6 and the 5Z4 were removed from the chassis.

I didn't try bridging the electrolytics yet, but I'm not sure what you mean by that, do you want me to bridge all of the ground connections from the electrolytics?
If so I'm not sure how I would go about doing that seeing as all of them are grounded to the chassis in some way, shape, or form so they should technically already be bridged, seeing as the chassis is the common ground in this case.

[old_coot88]

Bridging simply means "connect in parallel with", using a pair of clip leads. So bridge (jumper) each individual electrolytic (one at a time) with a single unit of equivalent or higher ratings. Note correct polarity.

The caps in question would be C19 and C20 (main power supply filters). You could jumper each with something like a 20mf 450V unit and see if it affects the hum.

EDIT. Those two caps should be replaced as a matter of course anyway. If they're the original cans they could be left in place for aesthetics, but out of circuit. There's also C26, a low voltage electrolytic across the cathode resistor of the 6F6. It won't cause a hum problem, but will cause reduced volume if it's gone open. It should be replaced anyway.

[vortalexfan]

Originally Posted by old_coot88

Bridging simply means "connect in parallel with", using a pair of clip leads. So bridge (jumper) each individual electrolytic (one at a time) with a single unit of equivalent or higher ratings. Note correct polarity.

The caps in question would be C19 and C20 (main power supply filters). You could jumper each with something like a 20mf 450V unit and see if it affects the hum.

EDIT. Those two caps should be replaced as a matter of course anyway. If they're the original cans they could be left in place for aesthetics, but out of circuit. There's also C26, a low voltage electrolytic across the cathode resistor of the 6F6. It won't cause a hum problem, but will cause reduced volume if it's gone open. It should be replaced anyway.

Its already been done, none of the electrolytics in the radio are original to the set, that was the first thing I did when I got this set, was replace the old electrolytics, which I left the old cans in place for aesthetics and wired in some new electrolytics which I installed onto some isolated terminal strips that I soldered ontop of the old electrolytic can's positive terminal (the terminal strip's attachment lug was isolated from the terminals so the original cans are still out of the circuit but are being used as an attachment point for the terminal strip for the new electrolytics without affecting the circuit, its a trick I learned from Mr. Carlson's Lab.)

I checked the capacitors that I installed in the radio and they still test good yet on my ESR Meter, (they mesured about 4-6 ohms ESR and they both are 2 4.7 MFD 450V axial lead electrolytics paralleled together to make 10 MFD at 450V).

And then the low voltage electrolytic is a 10/10 @ 160V Firecracker type electrolytic cap like the original was, and that one tests fine as well.

So unless one of these caps failed in a manner I'm not aware of, or that the ESR meter wasn't able to detect (dead shorted) then I don't think the electrolytics are to blame here.

[dieseljeep]

Originally Posted by vortalexfan

Its already been done, none of the electrolytics in the radio are original to the set, that was the first thing I did when I got this set, was replace the old electrolytics, which I left the old cans in place for aesthetics and wired in some new electrolytics which I installed onto some isolated terminal strips that I soldered ontop of the old electrolytic can's positive terminal (the terminal strip's attachment lug was isolated from the terminals so the original cans are still out of the circuit but are being used as an attachment point for the terminal strip for the new electrolytics without affecting the circuit, its a trick I learned from Mr. Carlson's Lab.)

I checked the capacitors that I installed in the radio and they still test good yet on my ESR Meter, (they mesured about 4-6 ohms ESR and they both are 2 4.7 MFD 450V axial lead electrolytics paralleled together to make 10 MFD at 450V).

And then the low voltage electrolytic is a 10/10 @ 160V Firecracker type electrolytic cap like the original was, and that one tests fine as well.

So unless one of these caps failed in a manner I'm not aware of, or that the ESR meter wasn't able to detect (dead shorted) then I don't think the electrolytics are to blame here.

Remove the rectifier tube and check the HV windings on pins 4&6. Should be around 600 volts AC or 300 volts from either 4 or 6 to ground. If it seems to be in order, replace the 5Z4 with a 5Y3. Maybe the 5Z4 got damaged!
I would leave the 5Y3 in there! I don't trust the old-time metal rectifiers!

[Electronic M]

Originally Posted by vortalexfan

Its already been done, none of the electrolytics in the radio are original to the set, that was the first thing I did when I got this set, was replace the old electrolytics, which I left the old cans in place for aesthetics and wired in some new electrolytics which I installed onto some isolated terminal strips that I soldered ontop of the old electrolytic can's positive terminal (the terminal strip's attachment lug was isolated from the terminals so the original cans are still out of the circuit but are being used as an attachment point for the terminal strip for the new electrolytics without affecting the circuit, its a trick I learned from Mr. Carlson's Lab.)

.

If the negative of the can is grounded you could alternately solder the terminal strip to the chassis so the mount lug of the strip can be used for a negative terminal...you need a powerful iron to do it that way but it can clean things up a bit in some cases.

[old_coot88]

With an ohmmeter set to RX1, be sure the negative ends of C19 and C20 are securely grounded (zero ohms) to chassis. Any resistance here would definitely produce ripple in the B+.