Amp: Can I mix tubes from different manufacturers?

I have a KR Audio VT8000 monos power amp which use a pair of 6550 (or KT88) for each mono amp.

I had a very expensive quad set of KR KT88 tubes but one of the tubes recently failed and thus leaving me with only 3 KR KT88 tubes. I do have a quad set of GE 6550 A and a quad set of Gold lions 6550. I do not want to invest in KR tubes anymore.

My amp is self biasing (auto bias).

My question to you guys is: can I complete the quad set in my amp by supplementing the 3 KR tubes with another non-KR tube (i.e. Gold lion 6550)?
Are there any likely technical complications for my amp or speaker other than potential degradation/differential of sound quality? Or maybe I can mix and match the KR and Gold lions in each monoamp (i.e. one KR and one Gold lion in each mono) thus giving me a identical channel outputs from both speakers.

Many thanks for inputs from those with first hand knowledge about such permutations.
I'm sure you can mix them, but won't you always be wondering if you are getting the best performance possible?

As with anything to do with this hobby, having at least matched pairs seems to be critical

When I had my tube amp I always purchased matched quads for the power side and matched pairs for the others.

I just reconciled myself to the matching aspect of tubes and bit the bullet - probably spent too much on tubes, but it sounded very nice

If you know the spec of the tubes you have you might find a vendor that will closely match a new tube for you.
Dont mix them. The plate impedance will be different. Just a matched set of good tubes. Jallen
Since your amp is self biasing you should be all right mixing tubes.
From talking to an experienced tube guru he advised me that you could mix power tubes from different manufacturers as long as you have the same tube set-up in both monoblocks. They should be identical on each side. Say One KR KT-88 and One GE 6550 tube in each monoblock.

If I was in the OP's situation I would just sell off the KR KT-88 tubes and use the matched quads or pairs available. My preference is matching quads or matched pairs on each monoblock if matched quads weren't a possibility.
Check with KR to see if the new KT-120 will work in your amp.
Jedinite24: many thanks for your suggestion regarding the need for identical combinations for each side. I'll do that and report the results. I have a lot of kt88/6550 tubes in stock and do not want to spend any more on tubes. Selling the 3 KR tubes and buying other tubes lead to complications regarding hassles, time and money.
Dont mix them. The plate impedance will be different. Just a matched set of good tubes. Jallen
Yes. you can mix/match tubes, but, only in pairs.