Model 20 power transformer - Printable Version

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+--- Thread: Model 20 power transformer (/showthread.php?tid=805)

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Model 20 power transformer - Danny - 10-26-2007

Ran into another model 20. Two in one month. What luck but unfortunatly this one has a bad power trans. 376V between pin 6 and 9 but only 40V between 6 and 12. Does Mouser or any other parts supply house have a reasonable facsimile that I could drop in there ? Thanks

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- Ron Ramirez - 10-26-2007

Hi Danny

Unfortunately, no.

You will need a power transformer with a center tapped high voltage winding, a 2.5V center-tapped winding, a 5V winding for the rectifier PLUS another 5V center-tapped winding for your 71A tubes.

I would suggest you consider having Heyboer Transformer custom-wind a replacement for you, if you plan to keep and use the radio.
http://www.heyboertransformers.com/index.shtml

A new transformer for your radio should cost around $100. The advantage of having a new one made is that you can have them design the primary for 125 or even 130 volts AC, instead of the 110-115 volts that the original was designed for. This will reduce the strain of higher than designed voltages on your old radio's circuitry due to today's higher line voltages.

Should you decide to pursue this, you will need the complete specifications for your transformer - physical size, mounting, and the voltages and currents required for each winding. I'll post the transformer specifications later.

Heyboer does excellent work. I've used their services twice so far, and would not hesitate to use them again. But be advised they do not provide a terminal board as the original had, only wire leads. You will either have to adapt the new transformer into the original bells and terminal board, or hook the wires into the radio circuitry, without a terminal board.

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- Ron Ramirez - 10-26-2007

Happened to have a 1941 Philco catalog (on PDF) handy, here's the specs of your power transformer:

5-3/8" high, 3-7/8" wide, 3-1/4" deep. You'll need to measure the spacing between the mounting holes on your transformer.

Primary - 110 volts, 50-60 cycles. (For your new one, specify 125 or 130 volts for the primary.)

High voltage - 700 volts center-tapped (also known as 350-0-350V), 80 mA DC

Filament #1 - 2.5V center-tapped, 7 amps

Filament #2 - 5V center-tapped, 2 amps

Filament #3 - 5V, 2 amps (for rectifier filament, no center tap)

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- Danny - 10-27-2007

Wow, Thanks for all the info Ron. You've done all the work for me. Now,
can I get you to pay for it too ? Darn, $100 is more than I've got to burn right
now. Oh well, It'll sit on the shelf until I can scrape up the bucks. Wish I was independently wealthy. Thanks again Ron.

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- Ron Ramirez - 10-27-2007

Ha ha, not hardly! You're no doubt read about my misadventures of last Saturday in Old Ron's Bar & Grill about picking up a 40-201; plus confiscatory Indiana property taxes are coming due, Christmas is coming soon, ad nauseum...I have my own "no money blues" I could be singing. So, I feel your pain.

There are a lot of Model 20 chassis out there. You might try your luck with one of those. Or, use the power transformer from a Model 96, convert the output tubes to Type 45, and put that chassis in your 21 cabinet - you'll have a Model 21 Franken-Philco.

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- Danny - 10-27-2007

I did read about your travels and was wondering why, after the thermostat was replaced, did your car continue to overheat ? How to turn a 3 hour road trip into a 8 hour ordeal. While I have your attention, I've set aside that model 20 for now and picked up a little 42-PT49 that needs some attention. Tube complement is as follows 50L6-35Z3-7C6-7B7-7A8. I haven't been able to find a schematic for it. I've checked all the usual..Nostalgia ect ect no luck. Can you help??

[Image: http://img186.imagevenue.com/loc499/th_09112_Cabinet_Front_dial_scale_122_499lo.JPG][Image: http://img129.imagevenue.com/loc465/th_09154_Cabinet_Front_122_465lo.JPG][Image: http://img19.imagevenue.com/loc953/th_09155_Cabinet_Left_Front_122_953lo.JPG][Image: http://img169.imagevenue.com/loc1021/th_09161_Chassie_Parts_122_1021lo.JPG]

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- davemc - 10-29-2007

If willing to convert to 45's, take a look at this one sold by AES (P-T143).

Specifications
Rating: 350-0-350 V, 70 or 90 mA (if 5 V winding is used with 2 A rectifier)
Windings: 5 V, 3 A; 2.5 V, 7.5 A; 2.5 VCT, 3.5 A
Mounting Centers: 2.75" x 2"
Weight: 4.6 lbs.
Overall Height: 3.12"

The 2.5 volt windings can be paralleled or you can split up the 2.5 volt string into 2 strings. Might take some engineering to use it (45 bias), but at $64.25 you can save a little (on the other hand, getting 45's may cost you the difference vs. the solution suggested by Ron).

Oh well. Maybe waiting for a junker chassis is the best way to go!

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- Terry Judkins - 10-29-2007

RadioDaze has one for 45.00.
http://www.radiodaze.com/RD-transformer01.htm

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- davemc - 11-02-2007

Model 20 power transformer on eBay as we speak: 250182986055

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- Danny - 11-10-2007

Davemc
No one bid on it. I sent an email and he still had it. Offered him 20.00 for it and I'm happy to say the transformer is on the way here to me...Another model 20 saved. Thanks for the heads up on the ebay posting....What a great bunch of guys on this forum. I'm so happy

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- Danny - 11-16-2007

Hi All
Just an update on that PT. Got it yesterday and just finished checking voltages. All is as expected. Got a good one so I'm going to have two
model 20's. One will be a FrankenPhilco model 20/70 but thats another story for another day. Thanks every one for the help.

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