French tranformers

for the DIY ST35, the Dynakit and every other PP EL84

French tranformers

Postby domi64 » Mon Jun 09, 2014 9:30 am

i'm living in France and very interested by ST35 construction!

I have 2 output transformers type TU101 "AUDAX" , they are made for push-pull EL84 tubes.

is there transformers can be utilised here?

i join french constructor notice

Thanks for your answer

IMGP0129.JPG (69.41 KiB) Viewed 6598 times
TU 101.jpg
TU 101.jpg (111.37 KiB) Viewed 6598 times
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Re: French tranformers

Postby EWBrown » Mon Jun 09, 2014 10:38 am

Those output transformers should work vey well, even with their 10 Watts power rating. The specifications for these transformers are excellent!

If you wish to operate at 10 Watts output, then you could utilize 325 to 330 VDC B+ in place of the "standard" ST35 operating parameter of 365 to 380 VDC,
and set the cathode current (bias) at 35 mA, for each EL84.

The power transformer should have steel end bells, or be toroid-wound, in order to prevent the magnetic-field coupling of the 50 Hz mains power on the power transformer's primary winding, into the output transformers, which would then create an "incurable" 50 Hz hum problem.

/e B
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Re: French tranformers

Postby dcriner » Mon Jun 09, 2014 8:01 pm

I would try the two different push-pull connections, and see which sounds the best. It may depend upon your speaker impedances. Chances are, I think, the 8000-ohm connection will result in lower distortion.
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Re: French tranformers

Postby cedricb » Tue Jun 10, 2014 1:59 am

the UL tap is at 25%, I thought the optimum for the ST35 was 43%
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Re: French tranformers

Postby Geek » Tue Jun 10, 2014 10:54 am

Nope! EL84 likes 20-25% UL. Even Edcor has a special tranny for them:

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Re: French tranformers

Postby domi64 » Wed Jun 11, 2014 5:52 am

Thanks for your answers!

i join an old (1961) schematics using this transformers...
PP EL84 & TU 101 juin 61.jpg
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