• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

SE Output xfmrs....who are the current suppliers for not many $$$

Hi all,

It's been 15 years since I last saw a thread on low priced, or reasonably priced output transformers, the last thread was great but some of the mfrs are gone, part numbers have changed etc.

I have decided to build a single ended tube amp, not sure which output tube yet but I have lots to choose from in stock. Under consideration are 2A3, 211, (242C, 276A, 261A all same size as 211). I would also consider 300B but would have to buy those, I have all the others I listed.

I have been looking around and re-reading the old thread and have found Edcor and Transcendar are still in business, James seems to be gone and some of the others mentioned are getting hard to find. Hammond is still going strong as well and I can get locally as they are a Canadian company.

So what is currently a decent quality SE output xfmr, either Asian or North American? Not looking for specific part numbers, more of a survey of current suppliers. Also don't want to buy the old classic megabuck partridges etc. I see on epay for a kilobuck per pair. Would be nice to find good ones less than $100 ea.

My other thought is to find an inexpensive already built amp with one of the listed tubes, then mod the crap out of it, or gut it and put in my own circuit and use the chassis and xfmrs etc.

Look forward to hearing your recommendations and if you have used them, your opinions of sound quality.

Cheers
 

Duke58

Member
2009-01-03 8:00 pm
Electra Print output transformers sound excellent on the 45 SET amp I recently built.

If you want cheap OPTs, scrounge the surplus businesses, scour the internet, go dumpster diving. There's an electronics surplus business nearby my house. They have shelves and boxes of transformers.

Compare the prices of the transformers to the price of a new or used good quality amplifier- I think that the price for Edcor, Electra Print, Hammond, etc. aren't that expensive, especially considering the time you'll spend looking for something cheap.
 

Nectarpuke

Member
2011-12-30 3:35 am
Edcor would probably be the cheapest, and get solid reviews here on the forum. Electraprints will certainly run you more money. If you are looking into using a DHT output stage the quality of the driver will likely be a bigger contributing factor than the OPT. I have had success using toroidal mains transformers as well. Namely in SET... but they do have special requirements to achieve satisfying bandwidth, and they can only be used in parafeed as they cannot handle any DC across the primary. They have high parasitic capacitance so you'll need your output biased with enough current to overcome any slew rate issues. With Antek 10VA models, I have found around 40mA to be adequate for over 30KHz. The most limiting factor with toroids is saturation of the core at low frequencies. For a 240 volt primary rated at 50Hz, you will only get 250Vpp of output swing at 20Hz. I have been very happy with the $10 Anteks, I cannot speak for other manufacturers.
 
Last edited:
Toroidy in Poland makes SE toroids. I have not used them but my experience with the quality of their PP and power transformers has been very good. They also offered excellent service and reasonable shipping. It’s at least worth a look at their web site.

I've been waiting to get a pair of those. I've often wondered, what do they have to do specifically in the winding method to get a torroid to tolerate SE DC? Is it the just the same concept of creating an air gap somewhere like an EI?
 

6A3sUMMER

Member
2016-06-07 6:50 am
My first SE amplifier used a triode wired EL34 output tube for each channel.
I did not have an SE transformer, so . . .
I took a push pull output transformer and pulled out all the laminations.
Then I re-stacked the laminations, all the E's on one side, a single or double layer of Kapton Tape (to give some spacing as an 'air' gap), and all the I's on the other side.
I connected one end of the primary to B+, and the other end of the primary to the EL34 plate.
The inductance with the new air gap was still enough to give good low frequency response, - 3dB at 15 Hz (-1 dB at 30 Hz).
That was a good transformer, at high frequencies it was -3dB at 60 kHz, about -1 dB at 45 kHz.
The bottom of the EL34 cathode's RC self bias network was connected to the 16 Ohm tap, that gave about -3 dB negative feedback, and that helped to give the wide bandwidth, and a better damping factor.
Pay attention to which ends of the primary go to B+ and to the EL34 plate, or else you have positive feedback, not negative feedback.
With it connected in the wrong phase, 3dB feedback will not oscillate, but the frequency response will be narrow, the damping factor will get worse, and the gain will go up (versus connecting it for negative feedback).

For later amplifiers, I used commercial SE output transformers from Electra Print and One Electron.

For push pull amplifiers, I used transformers from Hammond and Edcore.

Oh, also I had a pair of used output transformers taken off a Fisher model 500 or model 800 receiver.
Those were good ones too, the Fisher amplifiers used 7591's in pentode mode, and a 12AX7 as a gain stage and split load invertor.
That transformer had to be pretty good to work with pentode outputs, and lots of global negative feedback to give low distortion and reasonable output impedance.
They had superior open loop square wave response, so that that kind of amp topology did not become an oscillator.
 
Last edited:
The OP asked for OPT's that are Cheap.

Would be nice to find good ones less than $100 ea.

Then mentioned a list of tubes.

Under consideration are 2A3, 211, (242C, 276A, 261A

Everything but the 2A3 does not line up with "less than $100." Since the 211 and it's relatives prefer voltages in the 1000 volt+ range and require high impedance OPT's that cost $$$$.

It is possible to build a working 211 amp on 600 volts, but it is a compromise design. Mine runs on 1100 volts, uses a 10K ohm OPT and makes 40 WPC in A2. Not a low budget deal any more, nor a good choice for an inexperienced tube amp builder.

If the 3 to 5 watts that a 2A3 can deliver is enough, then I would look at Electra-Print, Transcendar, Edcor, One Electron, and Hammond in that order.

I currently have a TSE-II amp running old Chinese 2A3's at 380 volts (way over spec) and delivering almost 6 watts per channel. I have tried the Transcendar 300B transformers, the Edcor CSXE 25, and the Hammond 1628SEA.

My older first gen TSE runs Electra print OPT's with 300B's and I tested all of the previously mentioned OPT's in a "shootout" format with 5 or 6 people who did not know which transformer was being tested, only it's number. Turn around time was under a minute between tests. Musical selections were chosen up front by the reviewers, and voting was on a "per song" basis, then the whole test was re-run with the next song. Granted this is not an ideal test, but the best we could do at the time.

The Electra-Prints were the favorite, followed closely by the Transcendars. The One Electrons have a high primary DCR which costs output power, but sound good. They produce about 20% lower power than the E-P, Edcor, or Transcendar. The Hammond also costs about 10% power compared to the E-P, and has some HF rolloff issues.

I got my E-P's almost 15 years ago and they were $100 each then, so they are probably over the budget today.
 
Hello again,

Wow! Thank you al for the tremendous response, especially my fellow Canadians. Yes, a $50 part almost immediately becomes $100 landed, maybe more is it's over a few pounds.

You have all given me lots to check out now and consider, and I appreciate it.

George, I read your tests from 2006 and they were very helpful, glad you chimed in here, and is also why I asked the question as I thought there may be some unknown to me Chinese xfmrs that somebody has discovered to be a gem. Funny thing, shipping from China is cheaper for us than from the USA.

And as a retired broadcast engineer and ham, I have been working around HV for most of my life and have built/modded many amps, tube and SS and even had a mfring company for a few years building class A old school power amps, but I'm an engineer, not a sales guy, so it didn't go very far. :mad:

Anyway, we are heading into a massive blizzard of a storm here for a few days, temps to -30C and snow, it's just starting now...so I'll either have a lot of time to play audio, or if I can get out of the driveway tomorrow, be out plowing snow. :rolleyes:

As for tubes, I'm not stuck on the ones I have, although I only want to use true triodes. My 211s are NOS JAN spec United, still in the box, guessing from the 50's. The other similar sized tubes are about the same vintage but used. My 2A3s again about 16 or so NOS, RCA and Marconi JAN spec, and a mess of used ones as well. I have a couple of 801s, 809s, and a bunch of 810s (stepping into ham territory :D) I understand the 10K requirements for the 211s etc so for my first SET build, will stay with the lower power tubes. I have about a 20cu' box full of power and filament xfmrs as well, many oil filled caps 1,000V and higher, anywhere from 10-50uF each, many chokes etc so I really only need the OP xfmr and a nice chassis.

I have thought about modifying a P-P xfmr, but I don't have any of those either.

My speakers, well, all Altecs, VOTT A7-500, pair of Big Reds which have the 604E with Mastering Labs xover, 16 ohm, and Valencias, so 3-5W should be okay.

I'll check back soon, thanks again for all the help.

Cheers
 
Last edited:
I've been waiting to get a pair of those. I've often wondered, what do they have to do specifically in the winding method to get a torroid to tolerate SE DC? Is it the just the same concept of creating an air gap somewhere like an EI?

I’m not sure exactly what they do. The first company to do it as far as I recall was Plitron. They were much more $$ than Toroidy. I would like to try them as well, but it will be a while before I get around to an SE amp project.
 

Francois G

Member
Paid Member
2004-06-16 8:36 pm
Illinois
Toroidy in Poland makes SE toroids. I have not used them but my experience with the quality of their PP and power transformers has been very good. They also offered excellent service and reasonable shipping. It’s at least worth a look at their web site.

Second Toroidy although I have not used any of their SE transformers. I bought three pairs Toroidy PP transformers from Electronic components. Distributor, online shop – Transfer Multisort Elektronik, and they shipped packages under 5 kg to me in central US for US$9.90 per package. All orders reached me within 4 business days after ordering.

Check: TTG-KT88SE TOROIDY - Transformer: speaker | 40VA; O115x65mm; 0.01/56kHz; 250mA | TME - Electronic components
 
I've often wondered, what do they have to do specifically in the winding method to get a torroid to tolerate SE DC? Is it the just the same concept of creating an air gap somewhere like an EI?

Presumable they either buy gapped cores, or cut, deburr and glue them together again.
I dismantled a burned variac, the core was wound from several shorter stripes, some only a few windings.
For a pp OPT I rewound the core with 0,025mm foil between.
This, and winding it, was a total PITA, but I wanted to try out some other ideas also.
 

pl802

Member
2011-04-01 8:15 pm
london
After reading your #15 I feel like the master is approaching the student for assistance....I'm humbled by you.
I say Toroidy but fear post and packaging to Canada.
I have 3 sets from them.
PS Love your Altecs and envy your grandchildren who'll inherit them.
BTW what is your present amplifier or is that amplifiers?

Tubelab_com looking forward to the bashing those Toroidy's are going to get from you.
Lord have mercy!!!