51-934 code 122 - Printable Version

51-934 code 122 - Printable Version

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51-934 code 122 - philco4me - 08-25-2025

Hello
Was looking to add a safety cap but it looks like both plus and neg go to the same ground. See photo.
I am confused.
Thank you.

RE: 51-934 code 122 - RodB - 08-25-2025

I'm looking at the schematic from the Phorum Library and C42 is the capacitor to replace with a safety capacitor. There's no polarity for safety capacitors. C42 is a 0.04mfd capacitor, you can replace it with a 0.01mfd X1 safety capacitor. In this case I like to use the disc style capacitor.

RE: 51-934 code 122 - philco4me - 08-25-2025

Thanks for the reply but on the 122 I do Not see that. See photo unless you see something I’m missing

RE: 51-934 code 122 - philco4me - 08-25-2025

Dose anyone have a code 122 schematic ?

RE: 51-934 code 122 - philco4me - 08-25-2025

Or use two safety caps ??

RE: 51-934 code 122 - RodB - 08-25-2025

Is there a 0.04mfd capacitor attached to pin 3 of the 50C5?

Just looking at the photo isn't doing me any good since I don't know what tubes are in the picture. All I can identify is an IF can.

RE: 51-934 code 122 - RodB - 08-25-2025

Looking at the schematic I have shows production changes. C42 was removed from it's connection to the 35C5 (not 50C5) and replaced with a 0.047mfd cap across the hot side of the power line to chassis. That's where the safety capacitor should go. I'm assuming the power plug is polarized.

RE: 51-934 code 122 - philco4me - 08-25-2025

So replace the .047 with the safety cap ? And yea the plug was just replaced with a polarized.
Thank you all so much for the help

RE: 51-934 code 122 - philco4me - 08-25-2025

Also on the plug just to be sure the neutral was connected to the larger of the two holes where the plug goes into the connector.

RE: 51-934 code 122 - MrFixr55 - 08-25-2025

OK, I think that the IF cans that you see is the convertor, 1st IF Xformer and 1st IF Amp, based on the 47 Ohm resistor between Pin 7 and ground. The cap seen on this socket is the Screen Grid bias cap.

The weird thing seen are the 2 devices between each leg of the power interlock and chassis ground. I have not seen any schematic specifically labelled code 122. I have looked at both the Philco Library and Nostalgia Air schematic (Contains both the Rider's and Breitman's data) and all 3 of these look the same. The 2 devices between the interlock and ground certainly look like factory.

A couple of important things:

This is a HOT chassis set not a warm chassis. Almost all AC-DC AM-FM sets that I have run into (1 Arvin, 4 Zeniths and an RCA) are Hot chassis sets with interlocks and no metal showing, even chassis mount screws. Like almost all AC-DC sets, the power switch is on the Chassis side, not the power input side. Polarized plug or not, there will be a situation where the chassis is hot. If the neutral is switched, the chassis is at neutral level with the switch closed but hot due to the low resistance of cold heaters when the switch is open. You may want to put the switch on the hot side.

There are several capacitors between various spots in the heater string and ground, On the schematics and I suspect on your set, there are 2 caps between the power input (hot side) and chassis. One is a 100pF cap. The other is a 0.05uF cap. There are 2 caps because the 0.5uF cap may have a high impedance at high frequencies, necessitating the 100 pF cap.

In your set, one of the 2 caps(?) connected to the interlock is superfluous and it will be bypassed by the power switch, and there is no reason I can think of for having that device.

If you can't find the elusive Code 122 schematic, consider wiring the set it in conformance with the other schematic when you find differences that you can't resolve by inspection. The schematics in the Philcp Library and the Nostalgia Air site were for a released version so it should be licit.

I don't think that one can find a 100pF safety cap. I would just use one with a good voltage rating. IMHO, there is not a lot of current across a 100pF cap at 120V 60 Hz. Do definitely use a safety cap to replace the 0.04uF cap, and possibly other heater bypass caps if they are higher than 0.005uF.

If your set is documented on a label as using a 35C5, ensure that there is a resistor in the heater string. If there is no resistor and the tube complement is a 19C8, two 12AU6s, a 12BA5 and a 12AT7, the voltage drop across these tubes should be 67V. Adda a 35C5 and the drop is 102V, requiring a resistor, but with a 50C5 (having the same heater current as a 35C5), the drop is 117V.

Hope this helps.

RE: 51-934 code 122 - philco4me - 08-25-2025

Yes this helps and thank you very much. I will take extra care working on this.

RE: 51-934 code 122 - MrFixr55 - 08-25-2025

Hi Philco4Me,

One other thing. One of those devices between the interlock and ground is the 100pF cap. The other cap is likely up by the selenium rectifier.

RE: 51-934 code 122 - philco4me - 08-26-2025

Thank you so much for the information. It is very helpfull. The .047 cap had a plastic cover from the factory. I have never seen that before and it was cracked I’m sure by years of heat. I put it on my tester and it’s dead.
Thank you all for the help.

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

So I tried to power it on for the first time and it blew my breaker. When checking I looks like the join on my safety cap shorted. I dont see anything touching but is it possiable that the rectifier is shorted ? How can I test It ?

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

I don't know what or how a selenium rectifier shorts. I do know that when it does it takes several weeks to rid the room of the stink. That's usually one of the first items I replace with a 1N4007 diode.

Try lifting one leg of the safety cap, Check your wiring. You should have a dim bulb at minimum. Measuring across the power cord plug with the pilot lamp out of it's socket and power switch on you should have a couple hundred ohms or so.