2. amps-preamps
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Tube mixing

So what would happen (theoretically anyway) if in a "push pull" tube amp where each tube has its own bias pot, you stuck disparate tubes next to each other. I have 3 sets of power tubes...if I put 6550s and KT120s next to each other in each channel biased properly (or to the amp specs), or a KT88 next to a 6550 in 1-2-1-2 pairs...would this trigger cosmic calamity? Gear meltdown? Audio magazine subscription rejections? Would the tubes sit there and stare at each other in disgust? I'm not necessarily gonna try this, but it seems to be a way to get the advantages of different tubes ALL AT ONCE! Ha...and hmmmmmm....
wolf_garcia
mlsstl
1,435 posts
 
...but it seems to be a way to get the advantages of different tubes ALL AT ONCE!
That's one of those ideas that sounds great if you say it fast enough.

Rather like deciding your next car should have an 8 cylinder engine with 4 cylinders from a Chevy and 4 from a Ford to take advantage of the strong points of each.

That's usually not a good engineering approach. ;-)
wolf_garcia OP
6,695 posts
 
Hey...I'm not planning to try this as I assumed there would be good reasons not to but somebody had to ask (actually nobody HAD to ask), and now I know and I feel I've learned something. By the way...I'm sure some near sighted tube head has accidentally stuck similar but different tubes in something, so I feel this thread has performed an important public service.
hifitime
715 posts
 
I think the impedance mismatch alone may be a problem, causing either the push or pull side to have a different load. Even with the same bias load, the frequency response can also be different enough, to possibly overheat the output transformers. I've used two different brands in each side (same number), for a blend that I liked better. This was as much of a difference I have tried. But, I wouldn't risk a totally different tube in each push-pull side.
dekay's avatar
dekay
5,544 posts
 
That would be far-sighted (near-sighted means one sees well near)?
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