Bob -
Absolutely! I know of several occurrences of that specific failure.
It's certainly a possibility here, although since this failure occurred
after an extended period of transmitting, the meter shunt is the first
suspect. R59 dissipates 0.4W at 350 mA, and of course after years of
tuning up with even higher 'un-dipped' plate currents. It really should
be a 1W or even 2W for long term reliability.
The B5G5 is a 600V, 500 mA diode, so a 1N4005 is ok, and a 1N4007 is
usually cheaper. That diode is a real challenge to replace, too!! :-)
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 2-C/2-NT, 4-B, C-Line&
TR-4/C Service Supplement CDs
<www.k4oah.com>
Bob Loving wrote:
Hunter, et.al.:
I have a T-4XC that would produce output power for a period of time
and then, suddenly, no output. If the rig was turned off and allowed
to cool down, then turnd on, the output power would again appear.
Several minutes later, same thing... no output power.
In my case, CR19 in the cathode circuit of the driver, V4 (the
ubiquitous 12BY7), was intermittent. With the transmitter turned off
(and back to room temperature), a DMM in the "diode" function was used
to measure the forward conduction of the diode. The diode seemed
alright. Then, applying heat from a soldering iron to one lead of the
diode would produce an open. After the diode cooled, it would measure
alright again.
Upon removing the diode, I noticed there was a crack in the case.
Since I didn't have the B5G5 diode used by Drake, I substituted a
1N4005 (1A/600V). I don't think the exact part is too critical so any
silicon diode with sufficient current carrying capability (100 mA or
more) and reverse breakdown voltage rating (300 Vdc or more) should
work. Comments Garrey?
Bob K9JU
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