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Quick question.....I've changed Power Output tubes on my little Airtight Kt88 amp, which is NON-biasable.
Regarding the driver tubes, though they read fine at the antique-electronics-store-tester, I wonder if sagging driver tubes will eventually do anything negative to the O/P tubes or the amp.
Sorry if this is a real novice question, but thanks for replies.
Follow Ups:
It depends on the design. If direct coupled, then yes, drivers can upset output tubes bias if they are bad. If not, then the sound can still go bad.That said, again depending on the design and how hard they push the drivers, they might be expected to last a lot longer than the output tubes.
JD,Gotta agree with Osc... Driver tubes are just that, they drive the input signal to a level and impedance which is as close to optimum, for the power tubes to use (at least in theory).
Once, the "piazz" has gone out of the gain stage driver tubes, a lot of the gain is lost. The sparkle, quick response to transients, the good signal-to-noise ratio, and bass is gone, too. The system loses its dynamic quality.
Like water flowing downstream... If the headwaters are poor, the most spectular cliffs in the world can't rectify that problem & still give you a great waterfall. If the gain stages are weak or poorly designed; the power tubes can't rectify that and produce good overall tone.
If anything, I've seen tired power tubes make an "okay tone" provided the front end drivers are in excellent shape and the gain stage has components operating within a good designed operating range.
Ideally, you need: a good power supply, stable bias, good gain stage & phase inverter stage, PLUS healthy power tubes all working in harmony---to get the tone the designers of the unit were aiming for.
Remember this ditty? "You can't make Chicken Salad outta Chicken S*it."
Steven, I have looked up my Aussie alphbet and cannot find the letter * .
OLLY
Just thought I'd post the final result.....Even though input tubes tested OK at neighborhood electronic store, I thought there was some drag there and changed.
Big difference; the KT88 outputs (which are new) really needed the change of 12ax7 driver tubes to get the sag out.
Saggy ones were Mullard Cv4004's which got replaced by Tungsrams.
The Svet Kt88's are audibly relieved.
As it is, the Mullard Cv's lasted 2 yrs to the Svet Kt88's one year. Guess there's no reason to complain.
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