Mixing different tubes in a preamp

Does anyone have any experience with the results of mixing tubes from different manufacturers in a preamp? I have a BAT VK-31 which uses 6 6922s. I replaced the stock Sovteks with what I happen to have on hand, 2 pairs of Telefunkens and 1 pair of Mullards,, distributing them so that the left and right channels are symmetrical. The sound is fine to me, but I'm wondering whether anyone has actually performed this type of substitution in his or her own preamp, whichever brand, and can recount the results or would otherwise care to comment. I realize that the optimum arrangement would be 3 matched pairs from the same manufacturer, but I'm trying to avoid the expense. Thanks.
Lots of folks do this; some even experiment to find optimal location for each tube type.
I have a CJ premier 14, CJ used GE's and Sylvania's when they could get syl...now they use GE's and unmarked tubes that are labeled Gt Britain, which I'm assuming are Mullards.

I've used all Mullards, 2 Mullards and 2 Hitachi's, and stock GE and Sylvania, all offer a slightly different sonic picture. So I think you can mix n match as long as the tube type matches.

Go crazy with it, there is no harm in experimenting with different brands. I've even tried mixing 6922's with 6DJ8's in my former CAT pre...no problems with good results.

I do recommend better tubes for the inputs and decent tubes for the outputs (gain) sections. If you have a phono section place your best (or quietest) tubes there.

Have fun!