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Output transformer options in 2021?

StepheK

StepheK

AK Subscriber
Subscriber
I'm thinking about building another amp, and wondering who is still building the larger power transformers in 2021. Several of the manufacturers posted in the past seemed to have stopped production, and I'm not seeing a lot of options for exactly what I'm looking for, a 5K primary UL tapped SE capable of handling a KT88 @ 80ma safely with headroom. Edcor and Hammond are the two main ones, reading the big Hammond has some roll-off on the high end. I also see a 4.7K offering from Classic tone, not heard much about this 40-18080 model. I also see Electra-print is still making transformers and have a good reputation.

Anyway, just looking for some advice and to see what my options are.
 
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I recently saw on two sites that transformers for ST-70's are out of stock. AVA was one, the Ultravalve is temporarily out of stock due to lack of transformers. Maybe just waiting for another run.
 
Hammond makes push pull iron up to 280 watts. High power single ended transformers are going to be more of a specialty item, because it's not a conventional method of building.
Most of the time when someone sets out to build a amplifier above 15 watts they are using a push pull topology. It's much safer, in that you aren't in the 600 to 1000 volt plate supply territory. It's much cheaper, because the load is being split between two tubes, smaller, cheaper, more efficient devices can be used. Push pull, is likely to give you better bass response as well.
So the manufacturers of this stuff build what they know they can build and sell at a profit, and which the end user will find usefull.
On a single ended transformers the balancing act that the designer must perform becomes less and less stable as the power goes up, (core size increases).

One of my personal pet peeves is when people refer to single ended transformers as Ultralinear.
Ultralinear transformers were renown for their exceptional performance, Keroes Enterprises held the patent on it. They engineered some of the best transformers ever made. Was Keroes winding single ended transformers?

No, not a single one.
They aren't Ultralinear transformers they're single ended transformers with screen taps.
Ultralinear amps are all push pull.

In situations like yours, I pick up the phone.
People who actually make things, and are in business still answer their phone. Call arround to the smaller transformer manufacturers and tell them what you are looking for. It may be perfectly available just not listed online... I've found that to be the case in the performance audio, and performance motorcycle worlds. Those who really know what they are doing, likely arent spending all day polishing their website, and those who spend all day polishing their website likely couldn't build a tuna sandwich.
 
For SE work, if your design employs GNFB, then Electra-Print would be the best way to go. No other manufacturer within the common go-to names, or even any other manufacturer I'm aware of in the US is even a close second in that type of application. If you're not using GNFB, then those from lesser manufacturers may work passably well for you. If you go tapped screen however I's suggest you're back to Electra-Print, as the proper design of such a transformer requires more than just adding a tap on the winding.

Dave
 
trainbuftony said:
One of my personal pet peeves is when people refer to single ended transformers as Ultralinear...

In situations like yours, I pick up the phone.
People who actually make things, and are in business still answer their phone. Call around to the smaller transformer manufacturers and tell them what you are looking for.
Click to expand...

I'm fine with calling people and planned to. I was mainly asking for a list of companies who are still in business making them, as many of the companies that came up in a search are no longer doing this. Personal experience with the different manufacturers is also helpful, as I want this next project to be higher quality than my first one was.

I sure didn't mean to get anyone this upset. I'm new to this, and have seen manufacturers and respected folks like Kegger refer to his SE amps "with screen taps" as UL amps and didn't realize that could be a pet peeve. Sorry my request got under your skin.
 
Do the screen taps on an SE transformer accomplish the same things UL taps on push-pull ones do? IE output impedance more like a triode, but power output more like a pentode? Single ended amps are not a thing I've ever fooled with outside of the output stages of basic table radios and such like that.
 
It does sound like Electraprint might be a great option for round two. I'll gather some data and call them next week.
 
I have had Electra-Print transformers on my SE 2A3 amp for over a decade and really like their performance and sound. They certainly have sufficient bass in my application.

If (when) I were to build a SE pentode I would seriously consider regulated screen grids with GNFB; a couple of OD3 are ideal for the job.

trainbuftoon said:
They aren't Ultralinear transformers they're single ended transformers with screen taps.
Ultralinear amps are all push pull.
Click to expand...

Well, that's a new one for me. I suppose somebody has to decide these critical semantic issues.
 
trainbuftony said:
I've wanted to try some sowters for a while, but the price has caused me to sit it out.
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I know what you mean - however I do believe you get a premium product for your money. You'd have to spend an absolute fortune to get Sowter quality transformers in a finished amplifier. Given the quality of workmanship I've seen in your projects, I think you could totally justify a pair!

Speaking of great but expensive SE transformers, I wonder if Audio Note UK is still selling them separately. I haven't ever bought one of their transformers, but if they are the same as the ones used in their amplifiers it is another option strongly worth considering.
 
Transcendar makes great transformers. I've used their SE transformers in a couple amps, and I think they're great.
 
gadget73 said:
Do the screen taps on an SE transformer accomplish the same things UL taps on push-pull ones do? IE output impedance more like a triode, but power output more like a pentode?
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I would hazard a guess and say yes, since tying the screen in at a certain percentage of the plate signal offers a local feedback loop which changes the plate curves shape.
 
StepheK said:
Are they still in business?
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I bought a poor of output transformers and a power transformer from them this fall. They took a few weeks, and it sounded like they were busy. They have up to 20W SE 5K Opts with UL taps.
 
Ultralinear was a trade name. A slogan, so to speak. It was owned by Herb Keroses company Acrosound. Hence the Acrosound Ultralinear transformers of global acclaim. I own a few examples as well as a few original catalogs. In terms of the "Ultralinear" trade name, no there were never any single ended examples. So that all came about when hobbiests stuck the "Ultralinear" trade name on their single ended amps.

Theres no right or wrong way of looking at it.

Putting the Ultralinear name on a single ended design seems in my opinion to be an attempt to capitalize on a cool name which once meant outstanding quality.
Theres a manufacturer who prints Ultralinear on speakers. Doesn't mean Herb approves.
Sorry for the derailment.
 
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