The PHILCO Phorum
Output Transformer for Model 41-300 - Printable Version

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Output Transformer for Model 41-300 - hyounce - 08-31-2010

I find that I am in need of a replacement output transformer for my model 41-300. Can anyone provide me with either a transformer, or sufficient specifications to find an after market replacement?

Re: Output Transformer for Model 41-300 - Ron Ramirez - 09-01-2010

The original 32-7997 transformer has the following specifications:

Primary impedance 12,000 ohms; secondary 5 ohms; 10 watts.

You can use a Hammond HX-125D as a replacement, available from Radio Daze or Antique Electronic Supply.

Edit: You won't find a new transformer that has the feedback tap in the secondary which the original had. But that can be worked around; we can tell you how when you get your new transformer.

Re: Output Transformer for Model 41-300 - hyounce - 09-01-2010

Thanks, Ron.

I do have access to another output transformer, in a 39-55 Philco that I haven't finished restoring, due to the fact that I have been unable to find a suitable replacement for the drive spring in the remote controller. Would that transformer work in the interim?

Henry Younce

Re: Output Transformer for Model 41-300 - Ron Ramirez - 09-01-2010

According to the 1946 Philco parts catalog, both use the same output transformer. Make sure your 39-55 transformer is good before you go to the trouble of switching it from one chassis to the other! The audio output transformers in Philco sets that are mounted under the chassis are all prone to failure, much more so than the older ones (1938 and older) which were mounted on the speaker.

Re: Output Transformer for Model 41-300 - hyounce - 09-01-2010

Ron,

The transformer on the 39-55 is mounted externally (top of the chassis) and is labeled Philco 32-7997N. I'm assuming that the "N" reflects the external housing.

If I purchase the replacement transformer you suggested and hook up to the secondary terminals 1 and 4, which terminal would be used for the center tap?

Henry

Re: Output Transformer for Model 41-300 - Ron Ramirez - 09-01-2010

hyounce Wrote:The transformer on the 39-55 is mounted externally (top of the chassis) and is labeled Philco 32-7997N. I'm assuming that the "N" reflects the external housing.

Ignore the "N," the 32-7997 is what's important.

Quote:If I purchase the replacement transformer you suggested and hook up to the secondary terminals 1 and 4, which terminal would be used for the center tap?

See my first post in this thread, above.

That is not a center tap on the output; it is a feedback tap, meant to provide degenerative feedback to the audio circuitry as a means of reducing distortion.

I can put together a workaround for you, but I frankly do not have time right now...I'm up to my eyeballs in college work.

Re: Output Transformer for Model 41-300 - hyounce - 09-01-2010

Ron,
Been there and done that, too. Fortunately, that's all behind me, now.

Henry

Re: Output Transformer for Model 41-300 - mgutierres - 09-04-2010

Quote:The audio output transformers in Philco sets that are mounted under the chassis are all prone to failure, much more so than the older ones (1938 and older) which were mounted on the speaker.

I've had to replace the output transformers on my 41-295 and 40-180 while the one on my model 90 remains strong. Is the fact that those later ones are mounted under the chassis the reason they fail more often? Any advice on how to make them last longer?

Mike

RE: Output Transformer for Model 41-300 - rck46 - 09-23-2014

I just started working on a 41-300 and came across this thread when I found that the primary on my output transformer is also open.  In addition to the use of a Hammond HX-125D as a replacement would this Edcor also be suitable?  see/www.edcorusa.com/gxpp10-4-10k.  The Edcor is less costly.  Does anyone have any experience with the Edcor products?  Regardless of which one is used I will need some guidance on working around the secondary feedback tap referred to earlier in this thread.

Thanks, Bob

RE: Output Transformer for Model 41-300 - Arran - 09-24-2014

 The Edcor ones should be fine, and less expensive then the Hammond ones, at least the universal Hammond types. Either make is probably of better quality then the failure prone originals, not only because of improvements in materials and winding technology but because Philco probably farmed out their output transformer manufacturing to the lowest bidder. Many of the early Philco output transformers fail too, although not at the same rate as the 1939-42 ones, with the 1939-42 ones it's almost part of the restoration routine along with the paper caps, resistors, and the wiring. At least with a 41-300 model the end result is worth the effort, if you plan on keeping the set, probably not worth it for resale.
Regards
Arran

RE: Output Transformer for Model 41-300 - morzh - 09-24-2014

Edcor builds to order with longer (forgot, how many weeks) delivery, even their standard products.
Hammonds are typically stock.

RE: Output Transformer for Model 41-300 - codefox1 - 09-24-2014

Old tube radios are not that picky, so whatever you can scrounge, provided it will fit, and you correct whatever caused the initial failure will be probably be OK, maybe a little less volume if there is a mismatch. Only made a difference in some portables in my experience.

RE: Output Transformer for Model 41-300 - Arran - 09-25-2014

 I suppose one nice thing about Edcor is that if they are building things to order you could probably get a replacement wound with the feedback tap, supposedly they have several hundred transformer designs on file, if you are lucky they may already have it. It's also possible that one of their stock transformers has a feedback tap on the secondary, although it's more common for one to be on the primary. It isn't really a big deal even if they don't, one of they old tricks to obtain some inverse feedback was to connect an RC network from the output transformer secondary to the grid of the first audio tube, I think that this was what Ron was thinking of. One thing to note though is that there is a tradeoff from doing this in an amp that does not already have it, you reduce the power output level and have to compensate for it somewhat.
Regards
Arran

RE: Output Transformer for Model 41-300 - rck46 - 09-25-2014

Thanks for all the responses.

Codefox:  I have several small output transformers for AA5 radios but nothing for this application with a center tap in the primary and the feedback tap in the secondary.

I'm going to go with the Hammond because of space limitations plus by the time you add the shipping cost to the Edcor it is about the same as the Hammond from Radio Daze.  I have placed my order.

Arran:  I do not have the knowledge to make the circuit revisions you suggest for the feedback tap.  Can you or anyone help with specific instructions?

Circuit diagram is at http://www.nostalgiaair.org/PagesByModel/423/M0013423.pdf

Thanks, Bob

RE: Output Transformer for Model 41-300 - rck46 - 09-26-2014

I just found this solution over at Nostalgiaair.  http://www.nostalgiaair.org/Forums/Messages/536/M0071536.htm  Does it look reasonable?

Bob