[RichG]

Just another update.  Because of several tubes that were DOA, I started to check the power transformer windings for the correct ohm readings.  When I checked the HV secondary, my VTVM showed the hallmark reading of a leaky capacitor charging.  This should not happen as the HV secondary is isolated from the filter circuit.  I did some poking around the rectifier socket and found a burn mark.  When I poked at the burn, my probe went through the phenolic right between the plate connections for the 80 rectifier.  I suspect the burn allowed a path to the filament connection, which would allow a connection to the filter circuit.  Anyhow, since the socket has to be replaced, it seems better to replace it with an octal socket and replace the 80 with a 5Y3.  Any advice as to the type of octal socket, ceramic, plastic?  I may be able to get an octal socket from my local Vetco Electronics.
It looks as though someone replaced the line cord at some point.  Not sure, but I don't think it was done correctly and that, coupled with a leaky filter capacitor may have caused arcing that burned the socket.  I will be checking the other sockets for burn marks. 
Thanks!
Rich

[Chas]

Ceramic 4-pin for an 80. The wider spacing of the pins still remains helpful.

Do confirm the transformer is good by operating it without load, socket leads insulated. If it does not overheat in 1/2 hour, good...

Chas

[RichG]

Hi Chas,
I didn't know that the older 4 pin sockets were still available. I'll have to do some looking at various suppliers.  I thought a ceramic socket would be the better choice.  Since all the tubes have been removed, I can test the transformer under no load conditions.  I'll isolate the transformer primary so nothing else gets energized. I'll use my variac (AKA Adjust-A-Volt) to bring it up slowly just to make sure there are no other problems.
Thanks for the info.
Rich

[GarySP]

Ebay has several choices under "4 pin tube socket". Take care and BE HEALTHY! Gary

[Chas]

The "Variac" is fine or a "dim bulb" (100) watts), works too as it is evident that some high temps once existed. Will need a 1/2 hour at full voltage to access if there is low level short, Be SURE that pilot lamp sockets are not shorted. Transformer should be just slightly warm, no crackling, sizzling sounds.

Measure the distance between the rivets to find a socket that has matching holes. Use fiber washers under the nuts so not to strain porcelain. Bugger the ends of the threads with diagonals in event the hardware ever loosens the nut won't get by the spoiled threads...

I have some used porcelain 4-pin if you can't find the spacing. Or drill new holes. Some, old school sockets had an extra springs to grip the terminals... Transmitter tube sockets...

GL

Chas

[RichG]

Howdy,
Just another update on my progress (or lack thereof) and it's not good news. Underneath the chassis there are a number of splatter marks of a tar like substance, near the rectifier socket.  Because of the burn marks on the rectifier socket, I looked more carefully at the transformer.  I was able to easily remove the top cover.  I discovered that this transformer had seriously. and I mean seriously, overheated.  Whatever insulation that was used had melted and puddled in the cover.  I cut all the wires and removed the transformer.  I removed the bottom cover and it was nearly filled with melted 'stuff'.  All the windings measure pretty close to what is on the schematic except for the HV secondary.  It's supposed to be 160 ohms and measures 112. The, off center, center tap is supposed to measure 75 ohms to one HV leg and 85 ohms to the other. It measures 64 and 48 respectively.  Even though there is continuity, I suspect some of the HV windings are shorted deep inside. I did check, and all the windings are isolated from one another.  Not sure that would be the case with operating voltage applied.  I'm not even sure I want to test the transformer with a variac.  I don't trust that it has severely overheated and won't fail under load.  So, I will have to start looking around for a 'parts' chassis either a 39-54 or 39-116.  There may be other chassis that use the same transformer, but I'm not aware of any. I will not bother to do anymore work on this chassis as everything hinges on finding and installing a working power transformer.  Oh, forgot to mention the safety capacitor is a total short and it's part of a bakelite block.  I would try to take a look at the HV secondary, but it's buried underneath the LV filament windings. And before anyone asks, I'm not particularly interested in trying to re-wind the transformer.  That's definitely not in my wheelhouse.
If anyone has any suggestions, I'd sure appreciate it!
Thanks all!
Rich

[RichG]

Hi again,
Just realized I meant to look for a 39-55 chassis not a 39-54.  Must have fat fingered typing.  Also, it came to mind that I should check the field coil as it may have been affected by the disaster.  The filter caps would have been replaced anyway.  Two of them were leaking at some point and the other has a bulge in it.  Not quite sure what happened here, but I suspect that when someone replaced the line cord, they did not do it correctly.  Either that or one of the filter caps went bad and overloaded the HV winding.
Rich

[Brad Winder]

Hi Rich,
From my experience, unfortunately it is not uncommon to find the power transformer in the 39-116 to be overheated and possibly shorted. I have seen many examples that have either had their transformer replaced or are found with a damaged transformer. My thoughts on these are:
-For the physical size of the transformer and the demand this large chassis is putting on the transformer, they build up a lot of heat.
-The rubber wiring that was used by Philco and other manufacturers at that time deteriorated and shorted. The rubber coating turned rock hard, and the excessive heat accelerated the problem.

I am currently working on a 39-3116X which is the Canadian version of the 39-116X. Philco in Canada didn't use rubber covered wiring (Yay!!!) but on the 39-3116 chassis, they did source a number of specialized parts from the U.S. parent company, two of them being the power transformer and the selector lamp wiring harness. When I found this particular set, it had a replacement transformer haphazardly "installed" and I could tell from the burn marks under the chassis that a catastrophic end had come to the original transformer.

I was able to source a much beefier transformer to put in it...its from a late 40's Philco television! It has all the correct voltage windings, and it will juuuuuust fit into the chassis.

[RichG]

Hi Brad,
I had no idea that the overheating was problematic in this radio.  Do you know the part number of the transformer you plan to use?  I was surprised to find that the stock transformer HV secondary was only good for 131ma and the one 6.4 V secondary was good for 5A.  I did not check all the tubes filament draw, but 11 tubes must be running very close to 5A. Though the 1942 parts catalog shows the transformer is good for 14-15 tubes. The Thyratron has its own 2.5V 2.5A filament transformer.  I will check the motor transformer as it sits very close to the power transformer and may have been affected by the overheating. In looking through the parts catalog, I did see one transformer, 34-7455 for 15-16 tubes, that might fit the bill.  It has dual 6.3V and dual 5V filament windings and the HV winding will handle 180ma.  Not sure what chassis this was used in.
The existing transformer used cloth covered wires, though stiff, they are not compromised.  The chassis itself seems to have about 50% rubber and 50% cloth covered wiring. The worst rubber wiring is in the station lamps harness. 
I will not be doing any further work until I'm able to source a power transformer.  Which is kind of disappointing.
Thanks for the info.
Rich

[Brad Winder]

   
The transformer I located is from a Philco TV chassis, circa 1948. The part number is 32-8391

I do have the replacement transformer that was in the set when I bought it. It does work, and is larger than the original one. But it is an upright style, and therefore you would need to make an adapter plate to cover the hole. When I bought the set, the transformer was held in place by two bolts. The part number is PT-86

[RichG]

Hi Brad,
Thanks so much for the info!  Do you happen to have the specs for the PT-86 transformer?  I did not find a listing for that part number.  At least you've given me some ideas on transformers to look for.  I'll probably go looking on Ebay for some options.  The upright style mounting doesn't bother me.  There is enough room for that.  I'm sure I could probably make a cover plate for the chassis.  I'm not a purist, but I do like things to be neat and tidy as much as possible.
One thing does concern me though.  The existing transformer has an offset center tap. I'm wondering if this was due to the biasing requirements and would some changes be necessary to use a true center tap transformer.  Or am I just making more of this than is necessary.
Thanks.
Rich

[RichG]

Hi Brad,
I'd be interested in hearing how the replacement TV transformer worked out for you.  Were you able to get the proper biasing voltages?  For some reason, I'm still hung up on the asymmetrical center tap.  The schematic shows 85 ohms from one HV leg to the tap and the other HV leg shows 75 ohms.  I figure there must be some reason Philco did this.  So far, I haven't found any information on this type of transformer.  I tried to model it in LTSpice but can't figure out how to set it up properly.
Thanks,
Rich

[morzh]

It is not any more asymmetrical than all of the centertapped transformers are.

SImply speaking, the same number of turns, as the bobbin gets filled up, requires greater length due to the increased length of every next layer.
Therefore, the same number of turns will show different DC resistance.

[rfeenstra]

Ditto to morzh. I have rewound a couple of PT and have found the # of turns the same but DC resistance substantially different. Wire length is substantially different. Am rewinding an Atwater Kent 165 PT right now. Resistance readings were sort of close but enough different to question it. Wow, that thing was cooked inside. Really makes me question the long term reliability of these old transformers with old insulation. Yet, i have not had transformers fail on sets I have rebuilt. Fingers crossed! Good reason to add fuses to these old sets.