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Old 8th October 2021, 11:46 PM   #61
Tubelab_com is offline Tubelab_com  United States
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I think that it means that the transformers will perform quite well in their intended application which is a parallel pair of 300B's or a parallel pair of KT88's per transformer. They should work well in other applications that make a similar amount of power and draw a similar amount of current through the transformer.

The 300 mA and 60 watts are obviously a 1 KHz spec. I have not run 60 watts or 300 mA through these yet as it would take three BIG (26LW6) sweep tubes to get there without a meltdown event. I have seen 45 watts and 250 mA with good performance at 1KHz. The test was only for a few seconds as my 40 watt tubes were dissipating over 60 watts each.

I plan on using these in an SE amp build, but I'm not sure of the exact power level or tube count yet.
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Old 9th October 2021, 12:15 AM   #62
SpreadSpectrum is offline SpreadSpectrum  United States
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Sure, but I'm assuming they didn't specify 1kHz (maybe they did?). Obviously, a transformer will be capable of way more power at 1kHz than at the low end of audio.

Industry standard seems to be 30Hz power spec or sometimes 20Hz.

But as you say, stick to something close to the suggested application and you'll be fine.
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Old 9th October 2021, 11:23 AM   #63
Tubelab_com is offline Tubelab_com  United States
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As I have always said about OPT's.......size matters.

The Transcendar OPT's that I have weigh 2.2 Kg. They are a custom design created for a commercial 300B amp. They were sold as surplus when the amp company ceased production. When I got them the only specs were "300B, 3000 ohms, 75 mA, 10 watts max."

The Toroidys weigh 2.5 Kg which puts them in the same weight class, so their use for twice the number of 300B's is probably a bit of a stretch compared to the Transcendars, but they are probably conservatively rated.

I have a pair of Eastern Audio (Chinese) SE OPT's in the same size and weight class, and they are rated at "50 watts," Again, I can get 50 watts through them at 1 KHz, but far less at 30 Hz.

It is not even a fair game to compare The big 4 to 6 Kg OPT's like the Edcors and Hammonds to a 2 to 2.5 KG OPT's.

Years ago Plitron and Amplimo made OPT's with the "Vanderveen Design." He now markets his own OPT's. Rumor says that Toroidy is making something very similar, if not a direct copy.

The Toroidy's cost me $208 USD for the pair delivered to my address in the USA. ($176 for the transformers and $32 for shipping). For the delivered price, they are not a bad deal. If I had the budget I would order a pair of the 1250 ohm Edcors for a comparison, but that's not an option right now.
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Last edited by Tubelab_com; 9th October 2021 at 11:28 AM.
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Old 9th October 2021, 04:47 PM   #64
SpreadSpectrum is offline SpreadSpectrum  United States
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I've heard that the Vanderveen transformers are quite a bit cheaper than the ones that were sold from Plitron. I corresponded with someone who built a Unity-Coupled amp with the ones from Vanderveen and he paid significantly less than I paid for my transformers from Plitron.

I'm sure they're not as cheap as Toroidy but they seem much more reasonable now.
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Old 9th October 2021, 06:36 PM   #65
tomlang is offline tomlang  United States
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That was the UC amp I documented on AudioKarma.

Torusni transformatori - Uvod

AFAICT they are made with the same 11 herbs and spices as the ones that were made by plitron and amplimo...

Many of Toroidy's offerings are stocked by Electronic components. Distributor, online shop – Transfer Multisort Elektronik. On some USA holidays (memorial, july 4th...), they have a 15% off sale. Their standard shipping used to be $9.95 that allowed one transformer to be ordered and stay under the weight limit. Make two orders and save a few more bucks...

Last edited by tomlang; 9th October 2021 at 06:41 PM.
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Old 10th October 2021, 09:00 AM   #66
zintolo is offline zintolo  Italy
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Will those Toroidy’s KT88 PSE trafos handle three EL34 in parallel? At 400V with 10% a-g1 UNSET feedback and biased around 80% they should hit 140mA peak each, 420mA peak total. How will they perform on lows? Thanks
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Old 10th October 2021, 05:29 PM   #67
6A3sUMMER is offline 6A3sUMMER  United States
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zintolo,

Good question, I am not sure, but . . .
Let's put this in perspective.

How low of a frequency are you talking about?
A 32Hz organ pipe?
20Hz?
The world's biggest orchestral Thunder drum?
The 6Hz of the canon of the definitive 1812 Overture recorded by Telarc?
Oh, did I forget to mention the broken windows at the college where the canon was recorded?

If they do not saturate with 420mA peak at those low frequencies, go to church and thank God.

After that, get new speakers, not too many can handle all of that.
(During the late 1950s RCA recording of the 1812 Overture, they used a real canon. They had the recording monitor speakers turned up too high, and the woofer cones jumped out of the speaker baskets . . . live and learn).

Remember, do not use negative feedback that comes from the output secondary.
It will only make the saturation worse, because the feedback correction will pump even more current into the primary.

The quickest solution, turn the volume down a little bit.

Last edited by 6A3sUMMER; 10th October 2021 at 05:35 PM.
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Old 10th October 2021, 06:26 PM   #68
zintolo is offline zintolo  Italy
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Thanks 6A3sUMMER,

30 Hz of the low B string of a bass is the -3dB point of my speakers.
Having that transformer UL taps, feedback is taken from primary, that’s why I’m asking.
It’s not a matter of “pump da bass”, but on the performance of that specific OPT based on people that tested them.
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