The PHILCO Phorum
Output transformer - Printable Version

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Output transformer - rfeenstra - 11-11-2017

I'm working on a model 14, code 122 chassis with an output transformer that has an open winding on 1/2 of the primary.  Transformer part number is 32-7082-P.  Any ideas on a replacement?  DC resistance from the CT to the good side is about 180 ohms.

I don't have a cabinet for this radio and was wondering what style cabinet was used with the 14 chassis.  I periodically see empty cabinets for sale on ebay and if the right one comes along, I would like to purchase it.

RE: Output transformer - klondike98 - 11-11-2017

Welcome to the Phorum!
Icon_wave

I've moved this into the electronic restoration section. Someone else will have to answer your transformer question but you can see cabinet styles in the Gallery.

RE: Output transformer - Radioroslyn - 11-11-2017

Hi and welcome to the Phorun,
What you are looking for in a universal replacement transformer is 5900 ohms to a 1.25 ohm vc @10w. This transformer is some what lower in impedance as the output tube are connected as triodes w/the plate and screens tied together. In a normal configuration as pentodes it would be about 12,000 ohms to vc.

RE: Output transformer - rfeenstra - 11-11-2017

So the speaker impedance is 1.2 ohm?  Do you have any sources for such a transformer?   I haven't found all of the sources for parts for radios. I'm relatively new to this radio business though am quite familiar with tube type equipment.  I've been in the electronic organ repair business for decades.  I remember the days of brushing up against the B+ of a high powered tube amp.  Not pleasant.  Hope to not do that working on these things!

RE: Output transformer - rfeenstra - 11-11-2017

I found the 125D series on Antique Electronic Supply.  I can match up a 1.5 ohm VC to 5.4K primary.  Close enough?

Thanks for your input!

RE: Output transformer - Radioroslyn - 11-11-2017

Hmmm.. Just did a bit more looking in to it and found that there are two different version of the 14 chassis. The 14B (table model) has the three 42 tubes. It has the 5900 ohm pri. The other version (floor and chairside models) has two 42 that are pentode connected. It takes an 12-14K transformer. Which do you have?

Before you get busy replacing the output transformer I'd check the driver transformer (if your set has three 42 tubes). This transformer can be difficult to source and expensive. Wouldn't proceed till I had a cabinet. My 2c.

Go here: http://philcoradio.com/phorum/showthread.php?tid=215 and open the spkr zip file. You can find all the specs for your spkr and transformer.

RE: Output transformer - rfeenstra - 11-12-2017

Thanks for your help!  This chassis does have the 42 driver tube though there is no indication of the B model. I actually powered it up this evening (having changed all of the caps and resistors) and it came to life just fine (except that the output is low cuz of the transformer.)  Now to get it lined up.

My older brother had this chassis by his workbench when he was a kid.  I too used it back in the 60's.  I may leave it just the way it is for the nostalgia of it all!  It was fun to listen to the top 40 while watching the tubes glow in the dark.  I know the transformer was out back then already as you could pull one of the output tubes with no effect, but the other would kill the sound.  I ordered the universal replacement from Mouser this evening.  They had one in stock.  I hope it's close enough.  At least it should be better than what I have now.

Interestingly, the shadow meter works backwards.  Should the vane be straight with no power? Mine is bent to one side.  If it were straight with no power I think it would register correctly.  It doesn't move a lot though so the magnet may need a little help.

Thank you again for your help. I'm enjoying this phorum.  I have another Philco to rebuild as well - a model 96.  The help here will be great.

Rob

RE: Output transformer - Radioroslyn - 11-12-2017

Hi Rob,
> I know the transformer was out back then already as you could pull one of the output tubes with no effect, but the other would kill the sound. 
The 42 w/the bad winding connected to it is more than likely toasted. With applying screen voltage w/o plate voltage to it make the screen want to act as the plate would BUT it isn't able to handle very much dissipation so it glow red and dies[Image: http://philcoradio.com/phorum/images/smilies/icon_twisted.gif].
As one of my friends sez I have short arms and deep pockets I would have given this one a try: https://www.tubesandmore.com/products/transformer-output-8-w
I think ratio wise it's pretty close. $50 for a opt ...EECCKKK!

Have a 95 out in the shed myself it needs a tuning cap. Some idiot previous owner took it apart and put it back missing a bunch of hardware. It's near the bottom of the gitterdone list.  Its somewhat unique in that it's the first set to incorporate avc . The 96 is about identical electrically. Technical note when replacing the two 2mf filter cap in the power supply use 630v film caps not electrolytic. They can't take the ripple current for long and will short.

RE: Output transformer - Steve Davis - 11-12-2017

Quote:rfeenstra said
I don't have a cabinet for this radio and was wondering what style cabinet was used with the 14 chassis.  I periodically see empty cabinets for sale on ebay and if the right one comes along, I would like to purchase it.
 Rob, I could make a reproduction cabinet for your chassis.

Steve

RE: Output transformer - rfeenstra - 11-12-2017

I looked at that one and liked the price a lot better!  But, I ordered the other one that is closer to the specs of the speaker - that is if the speaker is truly about 1.5 ohms.  I'm used to the more standard 4 - 8 - 16 ohm stuff.

Thanks for the info on the filter caps.  I would have used electrolytics!  That may be the next project since I'm into Philco's right now. Or maybe an Atwater Kent 55 that I've had for years.

RE: Output transformer - rfeenstra - 11-12-2017

Steve, I sent you a PM.  I see you'r a flyer. Do you fly the chopper?  I fly a Comanche and a little home built.  My interests flit from one thing to another, flying, player pianos, radios and who know what else.  Right now it's radios!  The discouraging thing is the amount of AM noise in a modern home.  Almost impossible to listen to a restored radio!  I haven't found a decent solution short of turning everything off. Any suggestions?

RE: Output transformer - Steve Davis - 11-13-2017

Rob, yeah, that's me flying that old Bell. That picture was taken over forty years ago. The helicopter was an old "wood blade" 47G-2. I owned a Piper J-3 for several years and a Cessna 150 for a while. I'm also an A and P mechanic.

I'll get back to you on the cabinet.

Steve

RE: Output transformer - rfeenstra - 11-19-2017

Installed the Hammond 125D and it works fine.  It has the same size core so I was able to remove the surround and mount from both transformers and install the Philco mount around the new hammond transformer.  It looks at least a little more original.  Not that it really matters.  It turns out that though the speaker is vintage Philco, it is not original to this model chassis so originality is out the window!

RE: Output transformer - rfeenstra - 11-25-2017

For grins and giggles I disassembled the old transformer and unwound the primary and secondary. I found a couple of places where there were black spots where the wire was broken. Not only that, every time I measured the resistance of the half of the secondary that was intact, I got a different reading. While unwinding (and counting the layers and turns), the wire came apart with virtually no tension on it. Evidently Philco didn't use the highest quality wire or there wasn't better wire available. Or, years of expanding and contracting dramatically weakened the, what I calculate to be, 35 gauge wire. Both a micrometer measurement and a resistance check of several feet of primary wire indicates this size.

Again, for grins and giggles, I've decided to attempt to rewind the transformer. I figure it will be good practice for repairing an irreplaceable one in the future. Any recommendations on the insulating paper between layers of wire?

RE: Output transformer - EdHolland - 11-28-2017

I am have been using high quality tracing paper for interleaf paper.

https://www.amazon.com/gp/product/B000KNJ52G/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

It cuts and handles nicely, and is very close to the thickness (measured) of the original paper.