Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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Jim -
Loss of control bias in ANY transmitting tube is a problem.
The problem here (as in so much electronic equipment) is that
electrolytic capacitors have a finite lifetime. Unfortunately it's
WIDELY variable, and just about impossible to predict which cap is going
to last 50 years, and which will only last five years. Or less.!
The capacitors that are causing "most" of these failures are all over 25
years old, well past even the most optimistic reliability expectations.
Hams being hams, they will use them until they fail, rather than take
any sort of preventative maintenance steps.
Fusing is not quite that simple, since the short term peak currents
associated with off-resonance operation during tuning can be pretty
large. As with most fused circuits, it's a narrow line between blowing
when you lose bias and blowing every time you're a little slow tuning up!
Another problem is that the fuse may have to clear up to 700 VDC
depending upon the condition of the tube.
Bottom line is, keep your power supply in good condition (update ANY
"original" AC-4 with an AC-4R upgrade kit) and make sure your Cinch
connector is plugged in firmly and doesn't have to support the weight of
the entire power cable. You're good for another 10-20-30 years,
probably longer than you're gonna need the T-4X(any)!!
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B & C-Line Service Supplement CDs
<www.k4oah.com>
Jim F. wrote:
"Jim F." <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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I see that tube bias is a big problem in these
sets.
Any chance of fusing the cathode resistors
to would help stem the bias problem ?
Do you think a couple of cathode wired-in-series fuses
work ?
Jim
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