What specs do tube amp transformers need?

[Balog]

Idle thought as I was looking at the various DIY tube amp kits. It seems like the most expensive part of the average tube amp (especially the large >100 watt units) is the transformers. I'm a building engineer by trade so I have access to both a lot of scrap industrial transformers as well as industrial supply places that can order/make whatever I want for relatively cheap. However, I only work on AC line voltage and modern lighting and hvac fixtures, so the intricacies of tube amplification is still a foreign world to me.

Obviously the exact specs vary depending on how many of what kind of tubes you are running, but I'm hoping for a set of guidelines to get started on.

[BbbyBld]

Do you want to know how to specify a custom transformer or do you want to know what to look for in salvaged transformers?

[MAMMOTHvolume]

Originally Posted by Balog

Idle thought as I was looking at the various DIY tube amp kits. It seems like the most expensive part of the average tube amp (especially the large >100 watt units) is the transformers. I'm a building engineer by trade so I have access to both a lot of scrap industrial transformers as well as industrial supply places that can order/make whatever I want for relatively cheap. However, I only work on AC line voltage and modern lighting and hvac fixtures, so the intricacies of tube amplification is still a foreign world to me.

Obviously the exact specs vary depending on how many of what kind of tubes you are running, but I'm hoping for a set of guidelines to get started on.

look on valve datasheets, they'll tell you what voltages and current you'll need. They'll also list the ideal impedances for O/T's

[T-Bird]

Hi.

Basically, a fixed frequency transformer and a variable frequency transformer share only the basic construction, and neither can be used very well in the other application.

If You don't mind the hysteresis losses and other anomalies, normal transformer lamination materials can be used for audio transformers. Be that EI, C or toroid.

There's plenty of books written on the AF transformers, their design and construction, some can be found on-line, some are "book-only".

This is a good page to start from if tube amp/AF transformer design interests You:

Technical books online

Regards
Sam

[throbbinnut]

I don't think you're going to be able to re-purpose any industrial power transformers as tube output transformers. Even if you did find the exact turns ratio and tap layout you need (center-tapped primary for push-pull design), with the proper size wire and core size, it's not going to be interleaved so the fidelity won't be that great. I've used some old TV horizontal drive transformers as output transformers for old power triode low-wattage hifi amps, and they worked, but real output transformers work better.

Same kind of problems with using industrial power transformers as the power transformer in the amp - lack of shielding could be an issue, won't have all the taps you need, etc.

I ran down that road when I first started building amps, and I lucked into old tube TV replacement transformers that I used for tube amp power transformers, but I ended up buying the real McCoy for output transformers.

Chris

[Balog]

Originally Posted by BbbyBld

Do you want to know how to specify a custom transformer or do you want to know what to look for in salvaged transformers?

I want to build a tube amp for fun. The transformers are the most expensive part from what I've seen, so I'm hoping to save money on them. I've been scrapping a bunch of old transformers lately, and was wondering if any might be repurposed or not. Failing that, I can hopefully order a custom one for less than buying one retail as part of a kit.

Many thanks to everyone who's replied, looks like reusing one is out. Now to read up and call our suppliers to see what kind of deal I can get...

[BbbyBld]

I want to build a tube amp for fun. The transformers are the most expensive part from what I've seen, so I'm hoping to save money on them. I've been scrapping a bunch of old transformers lately, and was wondering if any might be repurposed or not. Failing that, I can hopefully order a custom one for less than buying one retail as part of a kit.

You'd have to buy several hundred to get a custom cheaper than a lot of the DIY project transformers out there.

You may be able to find an OEM transformer on ebay from somebody who fell for an aftermarket upgrade. I know for a fact that there are companies who buy Peavey (and other makes) guitar heads new, replace the transformers, and then re-sell the amp at a premium. Maybe one of those companies would sell you an OEM tranny for cheap.

You could possibly find a used amp cheap and rob the transformers.

[Balog]

Interesting, good point on the little diy kits and the power of buying in bulk. Might still be cheaper and better if I was doing a 300w or something crazy like that, but it might be better to get some experience first eh?

[T-Bird]

Hi.

Originally Posted by Balog

I want to build a tube amp for fun.

Great, gets usually very expensive, very fast though .

Originally Posted by Balog

so I'm hoping to save money on them. I've been scrapping a bunch of old transformers lately, and was wondering if any might be repurposed or not.

IME (as a cronic DIYaholic), DIY is very seldom a way to save money, regardless of the trade.

Originally Posted by Balog

Failing that, I can hopefully order a custom one for less than buying one retail as part of a kit.

You could, but I can't see how that's possible unless the company is specialized in cheap one-off trransformers using fully programmable CNC winders, a large selection of lamination materials etc.

Originally Posted by Balog

looks like reusing one is out. Now to read up and call our suppliers to see what kind of deal I can get...

IMHO, it's not out, just takes quite a bit of self educating and research. You won't find one "right out of the box" though, that's for sure. But You can use the laminations and wind your own.

Regards
Sam

[WingKL]

This unfinished article might have some information.

[Balog]

Great points T-Bird, I appreciate it.

That is an excellent article WingKL, so much to learn in all this.