Getting desperate looking for OPT

Alan0354

Super Member
Hi

I know I have been talking about this here. I am desperate to find a little more reasonable priced OPT with primary impedance between 2K to 2.5K to do the first run prototype for me design. I really don't want to spend over $700 for a pair of good OPT on the first try. The only one that is reasonable is Edcor that is $110 each. But through communication with Edcor, I am not too confident with them. I have not managed to find anything in between Edcor and the more exotic Lundahl/Sowter or even Plitron.

Only other a little more reasonable is SAC from Thailand:
SAC Thailand.JPG

Hammond has the 1650T that is 1.9K primary and it's $148 each + shipping. 1.9K is pushing it. More importantly, from things I read, Harmond is not exactly an upgrade to Edcor!!!!

I am output of ideas. Anyone have anything else? Or any more encouraging things to say about Edcor to make me feel better in buying the Edcor?
 
IMG_0791.JPG I am new here but have a lot of experience with diy and tube audio and horns,I have built over 100 amps and still learning,for opt I have tried everything
Besides finding some used opt via e pay ,edocor makes some damn good opt,I too was skeptical till I tried their se opt and was surprised ,although I dont know their pp transformers their prices are good,for diy and experimentation.
You don't specify how much current ,wattage and bandwidth you need,
Here is a pic of my se el 84 amp with edcore
 
Why buy something that you will likely loose on selling if you don't like it! Unless you want to rip it apart to see how it was wound etc?

Silk PP 10K 15W was really liked by an amp builder/designer of the Musical Machine 6V6 PP amp several years ago!
 
I have not read all of the recommendations and do not know if James Transformers have already been suggested. I stopped reading when the snake oil references began. And decided that I should share my simple experience that proved to me there are qualities to more expensive transformers that can make them worth the price.

I have an SE test rig for pentodes hooked up to multiple regulated supplies for preamp/driver, and power tube grid bias, screen voltage and plate voltage. I have quite a few SE transformers from different manufacturers.

I always used the cheaper transformers for my tests so I did not accidentally damage my expensive transformers. No matter how I adjusted the supplies I always got results that were much less than what I expected from the data sheets. I struggled to get 4 watts out of a 6V6 unless I went beyond max suggested voltages and currents.

After some browsing on this site I read about testing the efficiency of the transformer by calculating the power into and out of the transformer. What I found was that all of my less expensive transformers were typically < 70% efficient. The ones that I most commonly use for testing were ~63% efficient.

I decided it was time to unbox the James and Transcendar transformers and test them. I hooked them up for the test and played some audio to make sure I had the full chain working. I was quite surprised by the result. There was a presence and detail that was not there with the less expensive transformers. I did the power calculations and both the James and Transcendars were 90+% efficient. And now I was able to get very close to the data sheet values.

I speculate that the greater efficiency and other qualities of the transformers contributed to the improved presence and detail.

Transcendars are currently unavailable and I would not part with mine but James transformers are available. The prices are very reasonable and akin to the budget you have mentioned.

As a result of my experience with these tests I intend to buy some of the higher priced transformers for my daily listener amps.

Steve
 
View attachment 1057978 I am new here but have a lot of experience with diy and tube audio and horns,I have built over 100 amps and still learning,for opt I have tried everything
Besides finding some used opt via e pay ,edocor makes some damn good opt,I too was skeptical till I tried their se opt and was surprised ,although I dont know their pp transformers their prices are good,for diy and experimentation.
You don't specify how much current ,wattage and bandwidth you need,
Here is a pic of my se el 84 amp with edcore
I am doing push pull, I am using 2 pairs of 6L6GC running at 50mA bias current each. So it's 200mA total. I need a 100W transformer as my calculation is about 70W output before the transformer.

Regarding to BW, of cause I want it as high as possible. I just get what I can get.

Edcor is the cheapest bar none. I am not going to use Edcor for the final amp, this is going to be built on a wood board as prototype amp. I want to optimize the circuit before building into the real amp. I am every intention to spend over $700 for a pair of OPT for the real thing, but I just want to get something reasonable that I can at least get a taste of tube amp first.
 
How about going vintage OPTs?

Someone on AK should have some unused Magnavox OPTs....

I’d imagine there is lots of old gear that used PP 6v6 .....
 
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I have not read all of the recommendations and do not know if James Transformers have already been suggested. I stopped reading when the snake oil references began. And decided that I should share my simple experience that proved to me there are qualities to more expensive transformers that can make them worth the price.

I have an SE test rig for pentodes hooked up to multiple regulated supplies for preamp/driver, and power tube grid bias, screen voltage and plate voltage. I have quite a few SE transformers from different manufacturers.

I always used the cheaper transformers for my tests so I did not accidentally damage my expensive transformers. No matter how I adjusted the supplies I always got results that were much less than what I expected from the data sheets. I struggled to get 4 watts out of a 6V6 unless I went beyond max suggested voltages and currents.

After some browsing on this site I read about testing the efficiency of the transformer by calculating the power into and out of the transformer. What I found was that all of my less expensive transformers were typically < 70% efficient. The ones that I most commonly use for testing were ~63% efficient.

I decided it was time to unbox the James and Transcendar transformers and test them. I hooked them up for the test and played some audio to make sure I had the full chain working. I was quite surprised by the result. There was a presence and detail that was not there with the less expensive transformers. I did the power calculations and both the James and Transcendars were 90+% efficient. And now I was able to get very close to the data sheet values.

I speculate that the greater efficiency and other qualities of the transformers contributed to the improved presence and detail.

Transcendars are currently unavailable and I would not part with mine but James transformers are available. The prices are very reasonable and akin to the budget you have mentioned.

As a result of my experience with these tests I intend to buy some of the higher priced transformers for my daily listener amps.

Steve
I looked into James Transformers per your suggestion, they don't have anything close to the primary impedance of 2.2K I want. Their lowest is 3.4K.

You ever use Edcor?

The reasons I go to 2.2K are

1) using 2 pairs of 6L6GC so I get more bias current running to get a bigger class A region. In my design, I get the first 18W in pure class A before transition to class B. That I don't push the tubes to reduce distortion.

2) To get a transformer with lower primary impedance. The lower the impedance, the less turns the primary needs, less turns implies less parasitic, less requirement of more sections interleaving. Going from 4.4K to 2.2K primary reduces the number of turns by 0.707. That is if 4.4K primary needs 100 turns, 2.2K primary only need 70 turns. Less turns, less sectioning is needed, that you can get away with cheaper transformers.

In another way of looking at it, if the transformer is wound the same high standard, the one with lower primary impedance always have the edge in sound quality as it just has less parasitic when everything else is equal.

Honestly, efficiency is not that important for me, I overkill in using 2 pairs of 6L6GC to start, calculation gives me 70W, even if it is 63%, I still have 44W, still very respectable for a tube amp.
 
The Silk ones (SAC) are great. Quality at a good price.
The one I want is 14000THB/pair, that is 14,000/32.59 = $430USD/pair. That's not bad. I wonder what is the shipping to USA. I just wrote to them, I can't understand how they calculate using the EMS. FedEx seems to be very expensive.

Problem of buying from foreign countries is the shipping. eg. The Sowter I want is $335 ea, BUT after shipping, it's very close to $1000 a pair.

the only one that is cheap shipping is Plitron from Canada. but they are $350 ea, not cheap as a starter. I like that their frequency response is to 175KHz!!!
 
Honestly, if it were me, I'd give Edcor a whirl.
I hope someone that used Edcor PP OPT can comment, it is cheap, perfect for prototype, the problem is whether it's too cheap and give an unfair representation of tube amp. I understand it's only a prototype, but I afraid it might be so bad that I question whether I want to pursue tube amp anymore. So I need to have something that I can use to judge.

The comments on Edcor are all SE here, I am not doing SE. My speaker is not the easiest to drive either. I bought a kit amp that is SE and it sounded so crappy. I wasted $250 already. So even for the prototype, it has to have some standard.
 
Why buy something that you will likely loose on selling if you don't like it! Unless you want to rip it apart to see how it was wound etc?

Silk PP 10K 15W was really liked by an amp builder/designer of the Musical Machine 6V6 PP amp several years ago!

Is the Silk designed to run 2k5 loading at 200 mA? The S256's sure are; it is listed in their OE literature.

I doubt you'd loose buying a pair at auction, at least not much. However, I have a project out with a few friends, an S265Q with E-Linear modification for 10k a-a use in current production is about $150 each...:) M4 vs M6 is a cost bump...there is some good Si steel we will use; thinner means less eddy current loss. This buy will *NOT* be configurable for 2k5 a-a use though. Qty of 8 pcs gave us a small break in price.

The amp you mention was *MUSIC MACHINE* and I discussed with Eric the use of 16458 and 16309 outputs, as well as the known excellent S265Q...and he was happy enough with the Silk you mention to ignore the troubles acquiring test samples of the W5 OPT's. That amp ran single pair 6V6 in triode into the design 10k a-a load...not quite the requested 2k5 that is possible with the S265.

Keep in mind that the S265 was originally built with steel a bit lower in power output capability. The 4E27 amps, built around M6 SuPerOrthoSil are quite capable of exceeding the 40W spec down to 20 cps at 10k a-a load.
cheers,
Douglas
 
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The one I want is 14000THB/pair, that is 14,000/32.59 = $430USD/pair. That's not bad. I wonder what is the shipping to USA. I just wrote to them, I can't understand how they calculate using the EMS. FedEx seems to be very expensive.

Problem of buying from foreign countries is the shipping. eg. The Sowter I want is $335 ea, BUT after shipping, it's very close to $1000 a pair.

the only one that is cheap shipping is Plitron from Canada. but they are $350 ea, not cheap as a starter. I like that their frequency response is to 175KHz!!!

You could try hunting down a set of UTC LS-58s w/ 2.5K & 1.5K primary Z. They are ~15 lbs. each.

108344400_o1.jpg


108344400_o2.jpg
 
If you can get your hands on a Dynaco A470 (ST70) output transformer- it may be worth it, to experiment with putting an 8 ohm load on the 16 ohm tap, or a 4 ohm load on the 8 ohm tap. That would provide a 2.15K load to the output tubes.

Sure, the losses will be a little greater- but it might do very well on the bottom end. It would need to be tested on the high frequencies, though- that may not be as good with that loading.

Regards,
Gordon.
 
Is the amp going to have a global feedback loop that includes the output transformers? If yes get the best you can afford. If no the Edcors will probably be fine.
 
Is the amp going to have a global feedback loop that includes the output transformers? If yes get the best you can afford. If no the Edcors will probably be fine.

Would modify that with something like, 'that includes the secondary of the OPT's', as in signal that is developed through the P>S coupling. It is also dependent on how far forward in the amp it goes. For example, taking an OPT working into a 16R load, with its secondary CT( the 4R tap ) grounded and delivering it to both sides of the Williamson diff amp stage grids is a wee bit different than taking a SE signal all the way forward to the cathode of the input stage.
cheers,
Douglas
 
I think Hammond 1650 series output transformers do a fine job considering their cost. Not the be all end all, but the ones I used make a nice sounding amp, which is stable with lots of global negative feedback.

Those UTC transformers shown above - wow, I hope I come across some some day.
 
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