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Old 1st May 2013, 08:21 PM   #21
rongon is offline rongon  United States
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Quote:
Originally Posted by centraltexastubeguy View Post
Thanks for the comments, all. I would like to get back on topic which is: what are the best PP transformers in the 30-100W range. Based on personal experience, not just hearsay.
My reason for revealing a bit about the topology under consideration was to aid in the flow of input regarding transformer sources.
So, yes, a list of manufacturers but put thru the filter of individual experience. That will be greatly appreciated!
Thanks again!
Rene

For either PP triode or PP UL, Tango and Hashimoto have sounded best to me. I have also messed with vintage OPT's from UTC, Dyna, Scott and Fisher. The Tango and Hashimoto OPT's I've heard or used have far surpassed the vintage OPT's. I have not heard Electraprint or Sowter.

A friend built a simple PP EL84 amp with Edcor iron and said the OPT's sounded extremely good considering the price. I'd like to try a pair of those.

I hope that's the kind of opinion you were looking for.
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Old 4th May 2013, 11:11 PM   #22
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Indeed! Thanks so much! Nothing like personal experience attached to a name(s).

Due to their relatively low cost, it sure would be great if the Edcor off the shelf turns out to be good. I'll look into Tango and Hashimoto.
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Old 5th May 2013, 12:58 AM   #23
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A good friend of mine who has quite a nice lab full of high end test equipment allegedly did a valid comparison of a bunch of output trannies, and swore that the more expensive ones sounded better. When he stepped out of the room for a moment, his side kick buddy told me he was there and heard no difference at all between any of them...

I've been having very good luck with Hammond power and output transformers for years, for both high end hi-fi and guitar amps. I've only gotten one bad one in about 20, and I returned it for a replacement. I usually buy them through Antique Electronics in Arizona. Although I haven't tried the more expensive brands personally, I suspect that they are really just fool traps, much like fancy speaker wire. Really cool looking, with rare earth elements in the core (cobalt for ex.), maybe pure silver wire, etc., and on the bottom line not audibly better than hammond cheapos, at least not to my ears. My Hi-Fi tube amp only has a max of 12dB negative feedback (adjustable 0-12), so minimal distortion correction, and it sounds dam good to my ears.

I've been a hard core audio engineer since the 60's so I would think I would know how to judge sound, but to be fair, there are those who say they can hear the difference.

My guitar amps that I built using Hammond Hi-Fi transformers sound so much better than the other guitar amps in the band I'm in (2 other guitarists, Fender and Peavey, all tubes), it borders on being embarrassing. I'd worry more about getting the impedance match to the tubes right, and use a topology that has minimal crossover distortion when in clipping.

You can check out my "Musicbox" 30 watt per ch. Hi-Fi tube power amp at:
http://www.spiritone.com/~rob_369

Last edited by Bob Richards; 5th May 2013 at 01:00 AM. Reason: link didn't work.
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Old 5th May 2013, 02:07 AM   #24
BudP is offline BudP  United States
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Any of Edcor's units are competently designed and well built. Hammond is a bit more variable. Don't bother with the "high end" boutique makers like O-Netics, Intact Audio, Tribute Audio, Sowter, Lundahl etc, until you know exactly what you do not like about the Edcor product. Chances are very good you will never need to spend more.

Bud
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Old 5th May 2013, 02:38 AM   #25
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Great stuff, fellows! Thanks so much, I hope it keeps coming.

Rene
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Old 5th May 2013, 08:00 PM   #26
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the Edcor I didn't like for push-pull pentodes. the single ended for a 6em7 was good for them.


the Black enclosed hammond transformers I like them for push pull DHT and pentodes on more of the budget stuff. I've had manufacturing inconsistencies with the yellow bobbin ones.


If you want to build a higher end, Plitron or Hashimoto is the way to go for push-pull.
Otherwise, the black enclosed Hammond works good.
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Old 5th June 2014, 07:12 AM   #27
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A transformer with tertiary winding (bifilar with the primary)would be really nice for sweep tubes. There is a good small production/custom shop here that I could get a quote, would you guys be interested?
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Old 5th June 2014, 10:07 AM   #28
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Here a test from some "cheap" transformers.
Budget Output Transformers | Tubelab

Not PP but SE and you can see non of them are really good, but useable. At the other hand, those "high-end" manufactures don't give datasheets so maybe they not better.

Quote:
Originally Posted by BudP View Post
Any of Edcor's units are competently designed and well built. Hammond is a bit more variable. Don't bother with the "high end" boutique makers like O-Netics, Intact Audio, Tribute Audio, Sowter, Lundahl etc, until you know exactly what you do not like about the Edcor product. Chances are very good you will never need to spend more.

Bud

Last edited by esltransformer; 5th June 2014 at 10:12 AM.
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Old 6th June 2014, 01:41 PM   #29
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I've tested a couple of the 15-20W Hammonds and they were not very good, especially on the 8 Ohm tap. Dynacos and their recent clones were quite good, though beat by a number of vintage transformers - including some Scott, Fisher, Triad, UTC, Stancor, H-K and even some Bogen PA transformers.
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Old 6th June 2014, 03:21 PM   #30
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Good Morning to All from beautiful Central Texas:

Thanks so much for all the input! Time to reveal my more focused thoughts and musings, and also a bit more about my experience and expertise.

I make my living as an engineer in the MWD industry. There we have to deal with very high temperatures, power magnetics, signal and sensor magnetics (magnetometers, inductive sensors, others), low noise/high gain amplifiers, logic/microprocessor circuits, and the like, all operating at temperatures in excess of 175C. No typo, over 175C all the way to 200C. In other times I have designed many transformers and magnetics of all types, including pulse, power, ferroresonant, etc.

In spite of my qualifications, I wanted the collective wisdom and experience of this group. There are lots of you who have been there, done it and probably have the tee shirt to prove it. No way was I going to miss out on that. Thanks again for all the postings!

During all this time, my research has been bringing me to a very specific topology, and a reasonable vendor.

I believe that Edcor will give me the best bang for the buck, especially since I want a bit of a custom design. Nothing way out but still a bit of a change from the standard configurations. But first, the topology so it all makes better sense.

I just love the old treatises on vacuum tubes and amplifier theory, with all the heavy math and all. While my original thinking was toward a conventional UL output stage but with a "tertiary" winding (in quotes because that appellation depends on physical placement, functionality, and other things some of which are subjective to the designer) in order to accommodate the sweep tubes with their much lower Vg2, I have since highly modified all that.

If I were building it today, it will no longer be UL implemented with the transformer. Instead, it will have a regulated Vg2 supply with the ability, via MOSFETs, to apply a percentage of plate signal to the g2s. But, that could wind up being none, just straight DC (full pentode operation). The transformer will have a very mild CFB factor, but not a separate winding for that. Instead, the speaker secondary will be center tapped, taps pulled for my 6 Ohm speakers, and further symmetrical extensions for a very mild about 5% CFB. The drivers will be 6AU6 with both output plate to driver plate feedback (so called Schade) and output plate to driver cathode feedback. The 6AU6s will be driven by a fully differential input stage with sand state CCS. Overall feedback of about 6dB will be applied to one grid and the other grid is the signal input. The jury is still out on whether to use MOSFET source followers between the 6AU6s plates and the g1 of the output tubes. Grid stopper resistors will probably be adequate, plus the margin being built but if I wind up biasing more toward A than B then grid saturation is a real concern and the buffers would come in very handy in an overload situation.

So, error correction for the output stage, error correction for the driver/output combination and error correction for the whole thing. The total nested and overall feedback factor will be in the order of some 30dB. From my days of designing and implementing closed loop analog systems, that is about right to produce a very clean system. Additional tricks of resolving the OPT's resonance and providing a corrective network, shaping the frequency response of the chain and running Bode plots to make sure all the phase shifters are tamed will of course be applied. Differential all the way to improve CMRR, stabilize operating points against aging and other factors, and inherent even order harmonic distortion cancellation. Looks cool on paper so far, can't wait to have the time to actually build the beast!

Back to the transformer, my thought is to specify a 70W stack, pick the P-P load I want, specify the secondary per text above and other than asking for the secondary to be fully symmetrical (which probably means they'll have to either make it bifilar or in identical sections suitably connected) including DCR for my bias stabilizing scheme, they get to make it their way which according to many of you, it seems they know how to do it right. The 70W will give me margin since I only want 50W. The down side of heavy feedback is no tolerance for overloads. If anything saturates, the whole thing rapidly goes down the distortion drain. Like NOW. So, a 50W rating with about 70W capability and useage more in the 5W range. Running things in class AB1 will give me some 7W or so of straight class A1.

Thanks to all, keep the comments coming!

Rene
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