$100 for 2 tubes? And for the guy who said HIS tubes cost the same....not a realistic viewpoint. I just paid $106 for a set of 4 EL84's that used to cost $40
It is safe to do so. Just do not mix EL34 with 6L6 as that is not possible with the non-Simul Class amps. Not sure if that could be done with the V or the VII. I did a brief test with the STR440 and STR448. Did not hear much of a difference. Also keep the pairs as pairs. Easy to do with 100W amps as usually the inner pair should match and the outer pair should match. You can mix reds with yellows or others of the same type or different type as long as they are 6L6 tubes. Probably best to have a matched quad of tubes though. If the specs match for the plate voltage, no reason why you cannot run say a pair of TAD 6L6GCSTR with a pair of SED =C= 6L6GC tubes. Different tubes, different gain response and characteristics. Sometimes you either get not much of a change or something beyond expectations. However, Class A/B amps like the Roadster, MWDR or JP2C, mixing different 6L6 tubes may not achieve much. Usually with the Simul Class amps it can be different experience.That's great ! Thank you for these very detailed informations. I love STR440 in my Roadster and was afraid to be not able to find a similar replacement.
Did you also try and compare them in your MWDR ?
You mention that you plan to try a mix of tubes, like the STR440 + STR448 (or others combination). Is that safe to run two different pair of STR# together ?
Thank you very much for your very detailed answers, you rock !!! In conclusion, would you say that STR448 are sort of STR440 with a tighter character ?
I was also interested by your remark about grey vs yellow (STR440). What do you mean by they were too much ? I have some Yellow as a a spare but also Blu (that I never tested).
I also wonder how behave STR445 vs 448 in a Roadster (I found a YouTube video and they look tighter, with less low end). I love my STR440 but it seems no "new" tubes are really similar.