EL34 in a 6550 amp?

You may get more from this:
http://www.thegearpage.net/board/archive/index.php/t-214517.html

It depends upon the specific amplifier. Contact Jolida.

I own a 502B. 6550 and KT88s are interchangeable (have done that) but, to the best of my knowledge, without circuit modification, EL34s shouldn't be used in in the 502. On the other hand, the 302B is designed to run EL34s. Maybe things have changed recently but that's been my understanding. Why not contact JoLida directly (I'm sure they're well aware of what Shenda is doing) or Underwood HiFi (very knowledgeable) if your seller can't help?

Hi Hoestner,

To answer your question directly from experience. It can be made to work with both EL-34 and KT-88/6550 by changing 4 resistors in the bias circuit of the power-tubes.

The 502 comes with 4 * 20 k ohm for biasing. These should be changed to 15 k ohm if you want to use both EL-34 and KT-88's. The 302 comes with 12 k ohm resistors. 16 k would work as well. But I used 15 k and they adjust fine. I personally still like the KT-88's better.