Retubing my 2:90

Triaxis, Quad Preamp, Stereo Power series, Recto Preamp

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vitod
Bottle Rocket
Posts: 19
Joined: Sun Sep 20, 2009 10:43 am

Retubing my 2:90

Post by vitod » Tue Sep 22, 2009 9:52 am

Do all the tubes HAVE to be matched or it's just hype?

Thanks

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mr_fender
Mark III
Posts: 353
Joined: Tue Jan 02, 2007 2:50 pm
Location: Central Texas

Re: Retubing my 2:90

Post by mr_fender » Tue Sep 22, 2009 9:02 pm

For all 8 tubes, no. For individual push pull pairs, I'd say yes. Push pull amps require matched pairs of tubes for the best tone. Basically, the positive half of the signal uses one tube while the negative half uses the other. If the two tubes are not matched, you'll get crossover distortion and it will not sound its best. The 2:90's power tube layout is a little confusing. The pairs are arranged like this looking from the back of the amp:

----------------
- V1 V3 V5 V7
V2 V4 V6 V8
----------------

Tubes V1 through V4 are for channel A, and tubes V5 through V8 are for channel B. The matched pairs are oriented vertically and angled to the right, so V1 and V2 are matched, V3 and V4 are matched, V5 and V6 are matched, and V7 and V8 are matched.

Some say that for the most balanced stereo image the tube pairs for Channels A and B should be matched as well, but I'm not sure anyone would really notice with a fixed bias amp that has a "ballpark" bias setting anyway. Since all Boogie tubes are selected to be within a specific bias range, you shouldn't see any drastic differences from one matched pair to another.
Peace
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vitod
Bottle Rocket
Posts: 19
Joined: Sun Sep 20, 2009 10:43 am

Re: Retubing my 2:90

Post by vitod » Wed Sep 23, 2009 10:42 am

Thank you so much for that thorough explanation! Now to get the tubes! :mrgreen:

vitod
Bottle Rocket
Posts: 19
Joined: Sun Sep 20, 2009 10:43 am

Re: Retubing my 2:90

Post by vitod » Wed Sep 30, 2009 1:54 pm

Put in a fresh set of JJ retube.

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