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In Reply to: RE: KT-150 ??? posted by Nunki on March 16, 2017 at 11:22:06
If the amp has fixed bias, an overrated power supply and output transformers that can handle the extra output wattage, then the tubes could produce higher output. (Not likely unless homebuilt)
Follow Ups:
hmm...very strange...fixed bias plus constant anode voltage means constant output power! right?
or does not?
N.
"How the fuck did our oil come under their sand?"
To your question, look at the maximum possible voltage output across the load is. Ideally, for PP it is 2X that of B+. Not quite going to happen; can't get maximum load current at zero plate volts, yes? As the load goes from a-a/2 while both are conduction to a-a/4 when only one is, you are effectively looking at a bridged pair of SE amps...:)
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
Hmm, not quite. Bias voltage is one thing, actual current is another. Forget the KT120 or KT150 for the moment, and suppose you're installing a new fresh set of tubes, same model and make. A given bias voltage will not produce (or restrict, rather) the current in an equal fashion between the two sets of tubes. One set might have a higher current output (closer to an open circuit). For the same reasons, this is why one would adjust the bias as tubes age. As the use builds up, they lose life in the form of current output (and I think transconductance as a result), so you have raise your bias voltage (bring up the negative value closer to zero), to restore the output level. Of course, there's a point where this cannot be done anymore (limitation of bias circuit), and a new set of tubes is necessary. And, working from that point where you've adjusted the bias for older tubes, when installing a fresh set, you want to apply more negative bias to restrict the current to prevent an overload condition.
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May your tubes be lively, warm, and long-lasting. Holy be thy heater.
Edits: 03/17/17
"Of course, there's a point where this cannot be done anymore (limitation of bias circuit), and a new set of tubes is necessary"
By this time the space charge around the cathode will be depleted to the point where the tube is in serious danger of arcing. One of the challenges of trying to suck the last once of life from a set of output tubes. I know from experience. ;~)
"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln
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