Hi Guys,
I'm on my way to build PP EL84 amp based on Audio Note EL84 PP "inspired" PCB available in Aliexpress. It looks like a clone of the ANK Audiokits L1 EL84.
I'm straggling to make up my mind regarding output transformer. I’m looking for something economic, but not disappointing. There are so many options and I cannot make up my mind. I assume the experienced of you can give some orientation.
To start with, EI, C-core and toroids are offered- would you prefer one structure over the others?
Regarding suppliers- I read about Hammond (which are not liked due to their frequency response), Edcor, Lundahl (which are beyond my budget) and many other in between like Toroidy.pl., Triad.
On Ebay I can find old stuff like Siemens Klangfilm and some super cheapos from Indonesia or China.
You got the point… will appreciate any hints. I would like to stay below 100$ per OPT.
Another question- which power rating would be suitable for this design?
Regards,
Aviv.
I'm on my way to build PP EL84 amp based on Audio Note EL84 PP "inspired" PCB available in Aliexpress. It looks like a clone of the ANK Audiokits L1 EL84.
I'm straggling to make up my mind regarding output transformer. I’m looking for something economic, but not disappointing. There are so many options and I cannot make up my mind. I assume the experienced of you can give some orientation.
To start with, EI, C-core and toroids are offered- would you prefer one structure over the others?
Regarding suppliers- I read about Hammond (which are not liked due to their frequency response), Edcor, Lundahl (which are beyond my budget) and many other in between like Toroidy.pl., Triad.
On Ebay I can find old stuff like Siemens Klangfilm and some super cheapos from Indonesia or China.
You got the point… will appreciate any hints. I would like to stay below 100$ per OPT.
Another question- which power rating would be suitable for this design?
Regards,
Aviv.
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I am preparing a line of OT for different tubes included EL84
Soon I can send the details included the tests for freq. response and THD vs. frequencies.
That is very diffucult to obtain, normally.
Walter
Soon I can send the details included the tests for freq. response and THD vs. frequencies.
That is very diffucult to obtain, normally.
Walter
For 115 euro the toroidy output transformers come in a very attractive package, 67 euro for the standard toroid is hard to beat but then you'll probably want to hide them away
TTG-EL84PP - Tube output transformer [8kOhm] 2xEL84 Push-pull or similar - Shop Toroidy.pl
TTG-EL84PP - Tube output transformer [8kOhm] 2xEL84 Push-pull or similar - Shop Toroidy.pl
I believe these are some decent OPTs: ATRA0427 from Jan Wüstens
Frag Jan zuerst- Ask Jan first: Roehren und mehr
...although I never used them myself
Frag Jan zuerst- Ask Jan first: Roehren und mehr
...although I never used them myself
Never have used Jan's OPTs too, but I have an experience with his PTs and they are very decent indeed.
https://www.tbtroehrentrafo.com/produktseite/gegentaktübertrager-atr-30-für-el-84
Kind regards , Alexander .
Kind regards , Alexander .
I have limited experience with Jan's OPTs.
I use a Atra0288 which may or may not be available currently. I bought these as used items from DIYA member Yogi.
Quality seems good, bass response is supported fairly well, at a guess 45Hz or so, but there is quite a large resonance/group of resonances between 40kHz and 60kHz, which an OPT RC snubber will not completely compensate for.
The price/performance ratio seems to be good.
I use a Atra0288 which may or may not be available currently. I bought these as used items from DIYA member Yogi.
Quality seems good, bass response is supported fairly well, at a guess 45Hz or so, but there is quite a large resonance/group of resonances between 40kHz and 60kHz, which an OPT RC snubber will not completely compensate for.
The price/performance ratio seems to be good.
Thanks all for your recommendations.
The frequency of this toroid seems appealing in particular at low frequencies.
25Watt 8kOhm Push-Pull outputtransformer
However they also mention: "Full Power bandwidht starting at : 50Hz (25W)"
What do you think?
The frequency of this toroid seems appealing in particular at low frequencies.
25Watt 8kOhm Push-Pull outputtransformer
However they also mention: "Full Power bandwidht starting at : 50Hz (25W)"
What do you think?
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Looks like the G-series you've picked doesn't have screen taps for UL operation, if that's important to you. Toroidal Transformer Amplimo - toroidal-transformer.com
If you want screen taps go up their S-series, more expensive though.
Full power at 50Hz/25W. Will likely be a lower freq. at 12 to 15 W typical of an EL84 amp. Unless you have super-efficient speakers that go really low, 50Hz @ 25W is likely fine. Good luck!
Steve
If you want screen taps go up their S-series, more expensive though.
Full power at 50Hz/25W. Will likely be a lower freq. at 12 to 15 W typical of an EL84 amp. Unless you have super-efficient speakers that go really low, 50Hz @ 25W is likely fine. Good luck!
Steve
EL84 needs UL taps at about 23%.
Most UL transformers are at about 40%.
True UL operation requires a specific % number that is according to the specific tube model.
EL84 and EL34 are both true pentodes. But they need different UL tap % numbers.
Any incorrect % number is just negative feedback, but it is not True UL.
The only % number that works with all Beam Power tubes, and all Pentode tubes is 100% (Triode Wired).
But that is not UL either.
Most UL transformers are at about 40%.
True UL operation requires a specific % number that is according to the specific tube model.
EL84 and EL34 are both true pentodes. But they need different UL tap % numbers.
Any incorrect % number is just negative feedback, but it is not True UL.
The only % number that works with all Beam Power tubes, and all Pentode tubes is 100% (Triode Wired).
But that is not UL either.
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Pentode mode is the hardest on G2 screens.
Do not set the screen voltage higher than the maximum specs.
Triode mode is easiest on G2 screens.
UL mode is easier on G2 screens than Pentode mode.
Pentode Mode is generally the trickiest to set the Negative Feedback parts and parameters.
"All Generalizations Have Exceptions" - Me
Do not set the screen voltage higher than the maximum specs.
Triode mode is easiest on G2 screens.
UL mode is easier on G2 screens than Pentode mode.
Pentode Mode is generally the trickiest to set the Negative Feedback parts and parameters.
"All Generalizations Have Exceptions" - Me
Everyone who has knowledge about the manufacturing and winding techniques must admit that all these are not applicable with a toroid transformer.
So there are reasons why only some black sheeps decided to use them.
They will never perform and stand against a good Cut Core transformer or any other normal core type.
Per definition any toroid is unattractive for the experienced audio amateur with some wisdom from the transformer industry.
Personally I would prefer C-cores and would stay far away from the cheap designs. Cheap means cheap materials and winding methods.