The PHILCO Phorum
118X electrical overhaul - Printable Version

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118X electrical overhaul - Davros - 12-29-2016

Hello all! I am getting ready to restore the Mechanical portion of a Philco 118X Console. The overall condition of the chassis is intact, but evidence leads me to believe this radio was stored in an attic for a number of years. The capacitors all have leaked, and the wires are all pretty fragile. it also looks like some repairs were made far in the past, as evidenced by some spliced wires.

I have restored about a dozen AA5 style radios to good working order, but this is my first Pre-War radio. I think I have more in store for me than just changing out a few wax capacitors, and I would appreciate any advice more knowledgeable people could offer.

To start I do have the 4 page Service Bulletin #194 with the schematics and parts list. It states the model as 118, but it appears to be accurate to the 118X.

So for starters, there are a number of Philco Bakelite capacitors. I have read that they can be re stuffed, but they are fragile. Is this something I should undertake, or should I just replace the cap with modern? I have no spares, or donors.

Next there are square capacitors that I believe are Mica, In the past I have not replaced them, as mica are generally not failure prone. Is that true in these radios?

There is a shadow meter on this unit, is there anything special I need to do to make sure this works?

There is a part called a "wave trap" that looks like it has clear epoxy on it, What is a wave trap? Is the clear stuff normal?

Lastly, what do I need to look out for on this particular chassis? Is there anything in particular I need to watch for?

Thank you for your help!, I look forward to sharing the results of this work!

RE: 118X electrical overhaul - klondike98 - 12-29-2016

Welcome to the Phorum!
Icon_wave

Those bakelite blocks are not all that fragile. They can be broken but I've only had that happen on me once. There is a good thread on stuffing them at this LINK and another good reference at this LINK and at this THREAD. Its very convenient to restuff these blocks because they have the necessary lugs for the connections to the rest of the wiring.

There is some shadow meter information at this LINK and this LINK.

RE: 118X electrical overhaul - morzh - 12-30-2016

118 has very easily restuffable backelites. I finished one a few months ago. Unlike 60 I finished a week ago, those have some hard tar inside that stuck to the case pretty strongly.

"Good till proven bad" is true for all micas, no matter the radio.

The shadometer will show you nartow sector when turned on and then will go wide. If not (when the radio is working) then you will address it.

Don't scare yourself, do one thing at a time.

RE: 118X electrical overhaul - Radioroslyn - 12-30-2016

Hi and welcome to the Phorum,

<There is a shadow meter on this unit, is there anything special I need to do to make sure this works?
Well you can test the coil by measuring it's resistance w/o the  parallel resistor connected Should see about 1k or so if it measures much higher then it's time to rewind it. But like Mike said you don't need to bother w/it till later in the rebuild.

<There is a part called a "wave trap" that looks like it has clear epoxy on it, What is a wave trap? Is the clear stuff normal?
It's designed to trap waves! It is connected in series w/the ant and is adjust to block out signals that are at the IF frequency from being received from the ant. Back in the '30s and 40's there were lot of long wave stations these could cause interference w/broadcast listening if one was transmitting a the same frequency as your IF.

<Lastly, what do I need to look out for on this particular chassis? Is there anything in particular I need to watch for?
Lots of things but it may be easier to take them as come along.

For starters unplug the spkr and measure the resistance across all of the 4 pins. All should have some resistance between them like 2000 ohms or less. If not you may have a bad field coil or output transformer.

In the power supply the 10mfd cap inside #73 + side is connected the chassis (doesn't have to have a HV cap there this there is only about 35v there, would use a 50v). The other two filter caps the - connect to the HV ct.

http://www.nostalgiaair.org/pagesbymodel/125/M0013125.pdf

GL

RE: 118X electrical overhaul - Davros - 12-30-2016

Excellent!, Thanks for the speedy reply everyone!

I will start with a thorough cleaning.

and after reading the bakelite condenser references provided, I will order replacement caps, and start that task.

I will leave the Micas until later, or proven bad.

I will re-stuff the cans, and replace the rest of the old caps.

The wave trap, certainly looks like someone glued something there. I will have to take it off and clean it up.

I'll also check the speaker, it looks like its in terrific shape...

RE: 118X electrical overhaul - morzh - 12-30-2016

The wave trap - if the coil isn't open I wouldn't even touch it, it is non-essential today. If it is open (almost unheard of) - just short it out.
Don't touch it, or take it out, just light dusting if needed at all.

RE: 118X electrical overhaul - Davros - 12-30-2016

I will leave the wave trap for now. It's pretty weird looking though...

RE: 118X electrical overhaul - morzh - 12-30-2016

I agree.

RE: 118X electrical overhaul - Davros - 01-01-2017

I read out the speaker, and I believe I may have an issue with the Output transformer.

Reading from terminal to terminal I got the following readings

Two terminals in the green box read 1100 Ohms

Two terminals in the red box read open 

Two terminals in the yellow box read .02 ohms (Shorted)


If I am correct and these readings are bad, what are my options?

RE: 118X electrical overhaul - morzh - 01-01-2017

If you are lucky the 1100 ohm is your field coil. Then you only have to find a new transformer.
The transformer primary seems open.

RE: 118X electrical overhaul - Davros - 01-01-2017

OK, so the Field Coil is the terminals that are reading 1100, and the OPT is shot. (Verified)

Looking into the speaker, it looks like I'm in for a rebuild, as the inside is in bad shape, with the wires are pulled out from the speaker cone.

I would like to replace the speaker with a PM speaker. As I understand it, I can use the Field coil from the original speaker and not have to mess with resistors and chokes. Then I will replace the OPT with the following OPT https://www.tubesandmore.com/products/transformer-hammond-universal-push-pull-15-w-80-ma

(I chose this OPT as it has a wide variety of impedance to choose from depending on the Taps used)

I can even get my B+ from the same side of the Field coil as I can see where its tapped into the original OPT

Then replace the 10.5" speaker.

I may even cut out a new speaker board, and place the original speaker in the void of the cabinet attached to the board. That way I can always revert back if needed.

I took the following info from another post, and I am putting it here for easy reference.

The audio output transformer is Philco Part No. 32-7078.
Secondary impedance = 1.25 ohms
Primary impedance = 5,580 ohms
Primary D.C. resistance of the 32-7078 output transformer is 310 ohms (Philco Service Bulletin 180B)

Any issues with this plan?

RE: 118X electrical overhaul - morzh - 01-01-2017

Cumbersome.
I would recone the speaker. You need the transformer anyway.

RE: 118X electrical overhaul - Radioroslyn - 01-01-2017

Sound like a plan. The 125E should a good match for either an original or pm spkr. As a practical matter the resistance of the field coil is not very critical as it is in the positive leg of the p/s. Some sets the fc is connected to the HV ct and the negative bias voltage is developed across it. Theses are more critical it will effect the bias voltage.

Your set has what Philco calls there 10w high fidelity amplifier, it's p/p 42's wired in a triode configuration (plate and screen tied together) And a single 42 driver tube.Set up like this it delivers a good low distortion output. If in were in the standard pentode set up it would have more gain (would take less audio to drive it) but more distortion. Great for listening to some snappy tunes from Paul Whiteman's band!
Another thing to have a look at is the driver transformer. Sometimes they can have an open pri or sec.

A few of the big Philco sets have the 15w high fidelity amplifier which have larger triode tubes like 6A3's or 6B4's and a 14" spkr
https://www.youtube.com/watch?v=1w1P1VK9jGs

RE: 118X electrical overhaul - Davros - 01-02-2017

Thanks for the confirmation, and advice.

I have a 10" speaker laying around the house. I will use it in the scenario above, and if I am satisfied enough with how it all turns out, and I want to keep it 100% original, I will re-cone the speaker. Unless the sound is "Game Changing" over an original speaker in which case I will stay with my original plan.

RE: 118X electrical overhaul - Davros - 01-02-2017

So I just finish comparing the schematic to the actual chassis, and going over it looking for any trouble areas.

The IF transformers seem to have dripped out some of the wax from the inner winding's. (Photo below) Is this something I need to be concerned about? I don't plan on rewinding IF transformers...

The Wave trap "gunk" also appears to be a soft wax of some type, maybe dripped from somewhere, like another winding...

Lastly I stated before there may have been repairs at some time in the past. I located an 8uF 450V electrolytic capacitor that is not on the schematic.(Photo below) I don't know what the purpose was, but it's connected to the compensating condenser and the large wire-wound resistor. As the Cap is pretty ancient, is this something I should replace? Omit?