Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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Thomas -
I just re-read your message......
If the IDLE current is either Zero or 0.4A, with little adjustment, I'd
suspect the potentiometer has a break or "bad spot" on the resistive
element.
That behavior indicates that the Bias voltage is either some high value,
such as 70-80 Negative volts, cutting the final tubes off completely, or
somewhere around 30-40 Negative volts, allowing some 400 ma of idle
current, depending upon which side of the break the wiper is on.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B & C-Line Service Supplement CDs
<www.k4oah.com>
Thomas Wright wrote:
Maybe you guys can direct me a little. My AC3 has been showing signs
of bad caps, especially in the bias section ( one of the bias caps
measured at 700MFD). I replaced all the caps in all sections, using
33MFD 160 volt caps in the bias section, and while I was there did the
diodes. After reassembly the bias was adjustable from 41 or so to 80
volts. TR-4C was running well. Today after operating for an hour or
so, the transmitter started to show very high plate current, so I
checked the bias and found that it was either zero or above .4 amps,
without much adjustment between the two, and of course when higher the
xmit relay was engaging. Reducing xmit gain would not reduce the
plate current. I measured the voltage at the plug and the bias is now
only adjustable from 52 to 94 volts, which I think is too high.
There's not much else to replace in the AC3 except the bias pot and
two resistors, both of which measure within tolerance statically. Any
thoughts?
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