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51-934 code 122 - Printable Version

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RE: 51-934 code 122 - philco4me - 08-28-2025

Thank you for the reply I need To get a variac. Would anyone have a 122 code schematic ? Can’t seem to find one

RE: 51-934 code 122 - MrFixr55 - 08-28-2025

Hi Philco4Me,
Definitely cut out both caps that are across the power line., remove at least one tube and ohm across the power line with the switch closed. In one direction, you should read infinite. In the other direction, you should read an increasing number which will creep into the megohm region eventually. When cold, tubes will read a rather low value of resistance and as they heat, the resistance increases.

Others mention a "Dim Bulb" tester. This is easily constructed using an octagon box, an extension cord and a ceramic or plastic socket (the type commonly seen in an unfinished basement or garage) to mount to the octagon box. Cut the black wire of the extension cord and attach the wire leading from plug (line) side to the center contact terminal of the socket. Attach the black wire leading to the socket end of the cord to the shell terminal of the socket. The white and green wires should "pass through".

Obtain a 100 Watt Incandescent or halogen light bulb (if you can still find one) and put in the socket. Essentially, what you have done is that you have placed a 100 Watt bulb in series with a 30 Watt radio. If there is a serious short or overcurrent situation, the bulb will light brightly but you won't trip a breaker, burn out the power switch on the radio, etc. If the radio is OK, it may not play when plugged into the dim bulb tester, as it is likely to be getting only about 70 or so percent of the power needed. The following instructions assume that you replaced the filter caps, that they are at least 160WV (200 WV would be better) and you verified filter cap polarity, wiring, etc. In addition, verify that the wiring to the dial lamp, the bulb itself and the socket is not shorted. In the diagram, this shows as being line powered, not low voltage. The parts list describes it as a 117V 7 Watt frosted bulb, so it is likely a white frosted C7 Christmas Tree or Night Light style bulb.

To use the dim bulb tester, start out with all the tubes and EMI caps (Caps #42 and 40) removed. Cap 40 is one of those devices that are between the interlock and chassis ground. Remove that other device that goes from the other pin on the interlock to chassis ground. With these devices out and only the rectifier and filters in circuit, there should be very little draw. If there is high draw, break the connection between the rectifier and everything else. If still a high draw, the rectifier is shorted to chassis.

I have tried several sources for the Code 122 Schematic and am striking out. Unfortunately, not all changes are documented on several Philco sets and this may be one of them. A Philco memo of changes for 1951 and 1952 sets does not list a Code 122 for your set. However,,it does list certain 1952 AC-DC sets with the 122 code where Philco merely added a globar resistor in the heater string, replacing a 50C5 with a 35C5. The resistor has a high resistance when cold and the resistance decreases as the resistor (and string) heat up. If the label of your set shows a 35C5 instead of a 50C5, then you have this resistor. If it is bad, jumper it out and use a 50C5. This may be the only difference.

Hope this helps.

I don't think that there is a difference that if you miss the difference you will blow circuit breakers. This is one of the easier type problems.

RE: 51-934 code 122 - philco4me - 08-28-2025

Thank you so much. I am Going to do what you said and test. Just to be sure I tin The switch off plug it in then test ? Just want to be sure.

RE: 51-934 code 122 - MrFixr55 - 08-28-2025

Hi Philco4Me,

Switch off or switch on it doesn't matter. You will have to turn the switch on as part of the test. Have one of the knobs on on the volume control / switch and avoid touching the chassis.

Do not be working on a metal bench. Remember that this is a hot chassis set. Depending on the switch being open or closed and the "polarity" of the plug, the chassis touching ground could blow the breaker or your heart. Seriously, be careful. On hot chassis and warm chassis (Chassis connected to B- through a cap) sets, I always rewire so the switch is on the "Hot" side (Rectifier and 50C5 side) and that the chassis or B-, 1st Audio) is directly connected to neutral. Replace the cord with a polarized cord (Wide pin is neutral).

Consider replacing the selenium rectifier with a 1N4007. Put a 1A MDL fuse in series with the hot side of the power cord, before the switch. The voltage drop on a selenium rectifier is higher than that of a silicon diode but at this voltage, it is not critical.

Hope this helps.

RE: 51-934 code 122 - philco4me - 08-28-2025

A big help for sure. I am Working on a wood table so I’m good there. Thanks again and I’ll let you know how it goes.

RE: 51-934 code 122 - philco4me - 09-04-2025

So still have a dead short somewhere. I can’t seem to find it. I thought It was the light socket at first so I disconnected it but still have an issue. Any suggestion on this is much appreciated.

RE: 51-934 code 122 - bridkarl - 09-04-2025

Did you check the power cable and the switch? Start with the obvious. I assume by dead short you are getting nothing - dead radio.
Do you have an ammeter to check the current draw? Did you check the tubes for shorts using an ohmmeter across the filaments?

RE: 51-934 code 122 - RodB - 09-04-2025

Remove the plug from the power source, be sure the dial lamp is disconnected, connect an ohmmeter to the prongs on the plug. If there's a short you will see a reading on the meter of close to zero ohms. Now you have a visual indication of the problem. If this happened since you have been working on the radio then you have inadvertently caused the short, either from soldering or a frayed strand of wire or a bad part. Since you have removed the line caps and dial light there's just 2 possible circuits involved. One is the tube heater string and the other is the rectifier circuit. Remove the wire that goes from the power cord to the rectifier and see if the meter shows two or three hundred ohms. If so, then the short is in the circuit of the rectifier. If, after removing the wire to the rectifier, you still have zero ohms then the problem is in the heater string. Check each tube socket wiring especially in and around the heater pins. You have to use this process of elimination to get to the source of the problem. Don't apply power until you find and correct the problem.

RE: 51-934 code 122 - RodB - 09-04-2025

bridkarl - the power supply breaker is tripping, he has a short.

RE: 51-934 code 122 - philco4me - 09-04-2025

Replaced cord. get bright bulb dimm bulb when powered so I can’t keep power on to check anything. Have all the tubes out and don’t see any issue with power switch. Thank you for you reply not sure where else to look.

RE: 51-934 code 122 - philco4me - 09-04-2025

I thought The dial light was the issue but I took that out. I will Run the test you provided and thank you very much. I will Update this when I have A result. Thanks again

RE: 51-934 code 122 - philco4me - 09-04-2025

After I cut The rectifier wire do I test from the one wire still attached to the frame ?

RE: 51-934 code 122 - bridkarl - 09-04-2025

Is he on a GCFI? I’ve had those trip on perfectly good radios. Otherwise the advice above - follow it

RE: 51-934 code 122 - philco4me - 09-04-2025

Just a regular plug my set was DOA when I got It

RE: 51-934 code 122 - GarySP - 09-04-2025

The schematic in our Philco Radio Library located at the bottom of the page does not specifically reference the Code 122 run, but the production changes made in that run are documented in our schematic. Hope that helps. Take care, - Gary
https://philcoradio.com/library/index.php/service-info/philco-1951-home-radio-year-book/