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PrimaLuna ProLogue Two - mixing tubes?

I have a newer quad set of SED 6550Cs that I've been using as a replacement for the stock KT88 tubes. I decided to take advantage of the auto biasing feature of this amp and run one 6550 and one KT88 per channel, only because one of the stock KT88s is bad. I'd like to use up the other two good KT88s. I've read that this is acceptable with this amp, but I'm not sure if this will have negative impact on the 6550s. I plan to rotate the 6550s so that I still have a somewhat matched quad set of them. Has anyone done this before, and are there any pitfalls I should take note of?

Thanks
jwglista

Showing 2 responses by upscaleaudio

upscaleaudio's avatar
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upscaleaudio
258 posts
 
@Coltrane1, While PrimaLuna amps may not be directly designed to use several power tube types at the same time, the ability to do so is a pleasant side effect of our Adaptive AutoBias circuity. We've actually run 4 different power tubes at the same time in our own ProLogue Five, without any problems.

It will not damage the amp in any way, nor will it effect the longevity of the tubes... it's just not a practice we recommend, as it's not optimal in terms of sound quality.

We find this feature to be a useful tool for someone who's maybe throwing a party and has a tube failure... but the only spare power tube lying around is an EL34... that customer can put the EL34 into the circuit with KT88s (or whatever) and still have music going until a proper replacement can be had.
upscaleaudio's avatar
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upscaleaudio
258 posts
 
I never said it will sound nice. While using different tube types at the same time CAN be done in a PrimaLuna... that's not the same thing as sying it SHOULD be done. While you may blend the color of each tube, the slightly different operating parameters may make the sound less coherent and resolving.

I always recommend using only one type of power tube at a time. You can always change the 12AX7 or 12AU7 tubes to further fine-tune the color of the amp to your taste.
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