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Cheap xformer for tube output - OZ4 - 04-12-2018

I have never seen this one before. Here's a video on using a 70 volt line xformer as an tube output xformer. This guy shows how to calculate the impedance on the different winding's. He says they can be used for both single ended or push pull.
oops I forget to put in the link.
https://www.youtube.com/watch?v=-xrXjw7nt-g

RE: Cheap xformer for tube output - whirligig - 04-27-2018

I need to see if this will work on a Hallicrafters S-11. The original interstage transformer has a shorted winding. One side of the center tap is half the impedance of the other side causing one of the output tube to run scorching hot.

RE: Cheap xformer for tube output - Radioroslyn - 04-27-2018

https://www.tubesandmore.com/products/transformer-audio-interstage-10-ma

I'd give this a try. Line transformer is designed a relatively low impedance line to an even lower impedance voice coil.
At 10ma it's pretty close to the max plate of the 6R7. The ratio maybe a little high at 1:3, may need to load the sec w/a resistor across it. Price is good.

GL

RE: Cheap xformer for tube output - morzh - 04-27-2018

Well.
It is no good for pushpull. It is not really symmetric.
I once bought that "inexpensive" transformer which, when came, in the papers said it was the line xfmr. I needed one for my 90.
I checked the voltage, it was good 7 or so % asymmetrical.

The guy who sold it to me had no idea. He took it back.
I think in my 90 thread from, methinks, 4 years or so ago, I should've written about it.

RE: Cheap xformer for tube output - Arran - 04-28-2018

They had something about doing that in an old issue of the Antique Radio Classified, I didn't really pay too much attention as I thought it was rather impractical seeing that you can use a low voltage transformer to do much the same thing, even one removed from a "Wall Wart" power supply. However one of those line output jobs might work as an audio coupling transformer in some instances, depending on the ratios available.
Regards
Arran

RE: Cheap xformer for tube output - Phlogiston - 04-28-2018

(04-27-2018, 04:54 PM)Radioroslyn Wrote:  https://www.tubesandmore.com/products/transformer-audio-interstage-10-ma

I'd give this a try. Line transformer is designed a relatively low impedance line to an even lower impedance voice coil.
At 10ma it's pretty close to the max plate of the 6R7. The ratio maybe a little high at 1:3, may need to load the sec w/a resistor across it. Price is good.

GL

These are good. I've used at least 100 of them. They are a great replacement for 1920s and 30s radios where volume was more important than fidelity. Good price too.

But this is an interstage trans, not output - as in the thread title.

RE: Cheap xformer for tube output - codefox1 - 05-29-2018

Tube output stages are very forgiving, and there's no penalty for trying what you have. Of course, "portables" had little to spare in volume, so a mismatch in transformer or speaker impedence can be a problem. Agree, push pull outputs are a different story, not too many "other purpose" transformers can do the job, but within limits, no harm in trying.