Can you recommend a replacement power tube set for my 2/90/2. It currently has JJ 6550. I’m curious about which brands are reliable now for 6550 and KT88? Also is it possible to use KT90? Is it also possible to use, for example: a pair of 6550 in Amp A and KT88/90 in Amp B, at the same time?
My next question is whether or not anyone is able to provide me with a bias procedure? I have an oscilloscope, function generator, and a resistive power load available to use for this purpose. Thank you
Hi Collin,
We’ currently use Psvane and JJ 6550. We were using Sovtek 6550s previously but they have had increasing reliability issues, and of course, they’re from Russia.
All of these exhibit good reliability overall, but the Sovteks can cause crackling sounds initially.
JJKT88s are reliable but the sound leaves something to be desired. They tend to be mid forward.
We were using EHKT88s previously, but they have not been available for some time due to supplier issues. We haven’t had a lot of success with any of the Chinese produced KT88s. They sound good, but tend to be microphonic compared to the 6550s.
We haven’t evaluated KT90s is a long time, but they are generally fine and bias about the same as 6550s. Some of them can be awfully microphonic resulting in a low rumbling sound.
You can also use different power tubes of the same type (KT88/6550) and bias each channel accordingly.
Please see bias procedure below.
Dave
2902Bias.pdf (50.2 KB)