EL34 in a 6550 amp?

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.

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?

I don't have it yet. It will be delivered on Tuesday. Plus I don't even know which Jolida I got it from (Shenda or Maryland). The amp was designed for 6550, but they say a KT88 can be used as well. EL34 are supposed to be smoother so I was wondering if they would work also

It depends upon the specific amplifier. Contact Jolida.

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

Some amps that take EL 34s and can also accomodate KT-88s KT-90s KT77s and of course the 6CA7. Some will tell you that even the auto biased amps require some manual biasing to do this. It certainly makes intuitive sense that different bias voltages to the screens and plates for each tube would be required for them to operate optimally.
None the less I use KT-88s in my Jadis DA 60 which originally came to me used with EL 34s. I am not certain what it was built with however. I was informed KT 88s would work. They sound fabulous and are my favorite in this amp (GL reissues).
My thinking though was that transformers were more or less tube specific but I could just be running them at a lower plate voltage or something?? than is optimal. The bias is automatic and hard to set manually I have been told.
The only tube I have not rolled into this pin out is the KT-66. I am afraid to try that but understand that this whole family of power tubes was derived from that one.
Please correct me if I am wrong.

Well, you've received a no and yes so far.

What does the manual say about that? There are some amps that can use all 3 types, but if it's designed to get all there is out of an '88, probably it'll fry a '34.

Yes you can use el34

The amp would need a little modding to do so.