Transformer selection for stereo EL34?

I called Edcor once about custom winding some power transformers. They will do it but at a price. Once you order it they add it to their catalog for the next guy at the normal price. At least that's my understanding.

Last time I checked (several years ago) Heyboer will wind custom spec'd stuff for minimum additional charge. My experience is have them do it on their automated winding machinery with their best steel core material, even though you need to wait for corporate orders to complete so the machinery is freed up. You will get a more consistent result that way. Several pieces they hand wound for me had poor regulation properties (voltage sagged substantially under full load as opposed to no load). They redid those for me for no charge but still it took an extra few weeks of back and forth and it would have been just as easy to wait for the winding machinery to free up.
 
Just want to through this out:

At 50 watts, you are pushing the EL34's to maximum output. Designing to a somewhat lower output, like 35 watts (a common design goal for others using this tube) you will get longer service life and give up only about 1.5 dB of headroom. Just some food for thought.

Shelly_D

Agree with this. More power than 40w/ch, and you should really be looking at KT88s or 6550s.

As for transformers to use with EL34s- the Dyna Mk IV used the same A470 output transformers as the ST70, to get 40w/ch, full bandwidth. Those transformers have almost exemplary behavior when used in this fashion. That would make a really good 40w/ch, without breaking a sweat. All it takes is a stouter power supply than the ST70 had...

Regards,
Gordon.
 
Could definitely do worse than Dyna iron for EL34. Cloning the Mark IV would be a good way to do it too. I kinda like mono amps, no chance of power supply cross-talk, and its easier to feed a single channel than two. easier to move around too, all that iron gets heavy.
 
I'd be inclined to use Dave Gillespie's Eico HF60 mod circuit (triode input) with EL34s and A470s. I did exactly that- except for using a pair of rather unusual Sherwood output transformers that had UL taps buried inside (who would have thought?), and which were brought out in leads when BuzzK restored them (replaced all the wiring and refinished the outsides). That design worked very well, but didn't have as much power as it would with A470s (the Sherwoods were smaller). With the A470s and stout power supplies, it should easily be able to make 40w/ch, all day.

Regards,
Gordon.
 
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