70 V Line Matching Transformers

[Bloomfield]

I have three of these, nice NOS Peerless that a friend found while reorganising a music store basement. They have been sitting around for years as I haven't known what to do with them. Are they useful for anything (besides the obvious?) I saw an ebay listing claiming they could be used as output transformers, but the description was a bit confusing and sounded somewhat dubious.

Does anyone have any experience with re-purposing this type of transformer?

Thanks,

Andy

[mozz]

There is a Australian guitar amp building website (forum) that has a lot of info on the use of those. I would say figure out the impedance ratio and give them a try.

[Enzo]

I have never found them useful, but then I never took them on just as a challenge. I have used a zillion of them in my professional career, but I used them as intended, for CV speaker systems in commercial installations. (Restaurants, bars, stores)

[66 Kicks]

The attached may help. These things are Lo-Fi, but that doesn't mean they won't work for small guitar amps. They work well as reverb drivers where a restricted bandwidth is desirable.

[Helmholtz]

The attached may help. These things are Lo-Fi, but that doesn't mean they won't work for small guitar amps. They work well as reverb drivers where a restricted bandwidth is desirable.

As the 2k tap has half the turns count of the 8k winding, it could be used as the center tap in a PP amp with 2x6V6 or 2xEL84. I don't think the transformers would work well in single ended amps because they are not designed for the additional DC plate current.

[66 Kicks]

I don't think the transformers would work well in single ended amps because they are not designed for the additional DC plate current.

They seem to work fine as a single-ended reverb driver idling at 12mA.

[Helmholtz]

They seem to work fine as a single-ended reverb driver idling at 12mA.

Maybe, but I would expect a strongly reduced magnetizing or primary inductance leading to poor bass response.

Edit: I was referring to some SE output stage. Overlooked that you spoke of a very low power reverb driver.

[printer2]

The first P-P amp I made.









Good for about 4-5W more or less I guess. Looking at it today I would bump up the voltage 50V or more. Simplify all the switching stuff. I was just starting to mess around with tubes and this amp gave me an idea what different configurations sounded like.

[loudthud]

What are the primary (usually watts) and secondary (usually 4-8-16 Ohms) taps available on the transformer?

[Bloomfield]

Thanks for the replies. I haven't had a chance to look for that Australian site yet. I did just get the transformers out to look at though.

The large one, about the size of a 60W Hammond OT I have here, has primaries marked 8, 16, and 32 watts, and secondaries of 4, 8, 16 ohms.

The two smaller ones have primaries marked 30, 40, 60, 80, and 100W, and secondaries of 4 and 8 ohms. These ones also have capacitors connected to the primary common which are intended to be used as a high-pass filter. They can be easily removed.

[nevetslab]

At Cherokee Recording Studios, we used 25V Line Transformers to step up the output of the Crown D60's or D75's to drive headphone boxes. Phones are relatively higher impedance and like to see voltage. We used mic cables to distribute the headphone feed from these line xfmrs, with internally building out the headphone buss with 100 ohm 2W resistors. 4 stereo phones per box, XLR Female in, XLR Male out so you could daisy-chain them around the studio. The Peerless Line xfmrs normally had decent bandwidth, as they were the company making all the power and audio xfmrs for Altec Lansing.

[Bloomfield]

Here's the Australian site that mozz mentioned earlier if anyone is interested: http://ozvalveamps.org/optrans.htm

There is some good information there; I am going to do a little more experimenting at some point when I can put together a better set-up for testing them.

Andy