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Blown output transformer - Printable Version

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Blown output transformer - Tynwald - 10-26-2023

I started looking at a 46-132 battery set that I picked up awhile ago at a swap meet. Discovered that the output transformer had an open primary and was actually missing one of its leads from the secondary to the speaker. Looks like someone in the past started messing with it as the speaker leads had been disconnected, then likely gave up on it. The part number is 32-8152 but I can’t find any information on it in either the Philco Library or a couple of parts catalogs I’ve downloaded. If I can’t find the exact one, I’m curious if there’s another that could be substituted for it. It has a CT primary and is being driven by a pair of 1A5’s in push-pull.

Jon Tippin

RE: Blown output transformer - Radioroslyn - 10-26-2023

Seems the this transformer has a pretty high impedance primary at 50K. The load for each of the 1A5's is 25k. The highest thing that I could find is 25K to 4 ohm vc. https://www.tubesandmore.com/products/transformer-hammond-universal-push-pull  125A   or  https://www.ebay.com/itm/186125514312?hash=item2b55f1f648:g:m1kAAOSwNhZlBF5g&amdata=enc%3AAQAIAAAA4Hnf%2BTuLIPO6kUo3z7tAaIhvtcDvcK5NyelIJ8iwcbQM85NtJZBX96bT6a%2BZkHVaKwNccs6lWB5jCpwz8yGH69FHz0S%2FCCFQ2d0j1Hc1Z5MX7R6ASfM8EC%2BoKe39tMdG6COyl8hWnorMa3Twf7X%2BGIc9stVdh%2Fj939MJmDxv%2B7Pr4fm8Yn01fUdEyf%2BXS%2BLQkb%2B7955vn8S7n9lj%2FYEfassrs35Pi0EKQQ3X3DcgX0sqCCZxFdgBCs8E6fF4w6eB7dvAypBenCSsz73YKoqZflYFDOHpVQlkM%2FjCn7xgUcUI%7Ctkp%3ABk9SR_zGr-ntYg 

GL

RE: Blown output transformer - Radioroslyn - 10-27-2023

Something else to consider the 1A5 is good for abt 115mw of output ea. That's abt a 1/4 of a watt for the pair. You could swap those for 1C5'5 and be at the 1/2 w level. Same pinout and total plate load is 16K not 50K.

RE: Blown output transformer - radiorich - 10-27-2023

Hello Jon.
That is a great idea that Terry has it sounds like a winner .
Sincerely Richard

RE: Blown output transformer - Tynwald - 10-27-2023

Great suggestions! Think I’ll snag the NOS transformer on eBay and swap in the 1C5’s. Will the 25k be close enough with those tubes?

RE: Blown output transformer - Radioroslyn - 10-27-2023

Some else that was ruminating in my pea sized brain was if you keep the current draw close to the original spec you could go single ended w/one 1C5. It would still make more output by a nose. If you look @ the diagram the opt pri resistance is almost 2K. This means that there is almost a 15v drop in the plate voltage at the 1A5's.

Using the 1C5 the dc resistance of the replacement transformer is going to be something around 400 ohms (16k vs 50K) I would think. So the plate voltage @ the 1C5's is going to be higher than the 1A5's

With this lower resistance primary tubes (1C5's) are going to pull more current at 90v and make sound. But what if we removed one of them? If we use a opt for 8K to vc and coverup the bottom socket as shown on the diagram. Just use the top socket with a 1C5 it will make as much sound as it did w/the pair of 1A5's and it will keep the plate current down to 10ma or so. With the pair of 1C5's it will run your B batteries down quicker.

A quick note there is a big difference between dc resistance which you can measure w/an ohm meter across the winding of a transformer and the ac impedance. That is the ac load that the winding presents to a circuit. In this case the plate of the tube. The 1900 ohms that is shown on the diagram has nothing to do w/the ac load it presents to the plate of the 1A5, there is no correlation other than the higher the resistance the higher the impedance but this is a rough guess which is mostly true. The dc resistance is there to give you an idea what it should read and if it's open or not. That's it.

Somewhere around here I have a 48-145 which is the loctal version with se output stage. It a good player and impressive for the amount of battery juice it uses. Without being connected to the a p/s or a wall socket you don't get a lot of the noise that you hear on other set that plugin.

OBTW to answer your question I'm not sure. Because I don't know what the impedance of the vc is. That's the long answer. the short one is it's better than a an open one.

https://philcoradio.com/library/download/service%20info/yearbooks/1946-1947/split/Part6-Philco%20Home%20Radio%20Yearbook%201946-1947.pdf

https://philcoradio.com/library/download/service%20info/yearbooks/1946-1947/split/Part6-Philco%20Home%20Radio%20Yearbook%201946-1947.pdf

RE: Blown output transformer - Tynwald - 10-27-2023

Ha! That’s hilarious, yeah, anything’s better than nothing. There’s usually a lot of leeway in these impedance matches, so it’ll probably be OK. I initially thought I had the solution. Since one half of the primary was good relative to the CT, maybe I could just use that as I’m going to a single 1C5. But then I remembered that someone had yanked one of the secondary leads out. I thought about digging into it to see if I could find the end, but I’ve never been successful with that kind of thing. Darn…