SB401 Problem Help Please

[Mark Graalman WB8JKR]

I'd clean the relay contacts on both relays and make sure
the tube sockets are gripping the tube pins properly. Also
check and tighten the circuitboard to chassis hold down
screws.

Mark  WB8JKR


On Sun, 1 Dec 2002 17:13:41 EST Dan Pividal N4VET <OTAKEBI at AOL.COM>
writes:
> Have an SB401 that has an intermittent problem.
> The problem seems to take place if the SB401 is not used every day.
> If I use the rig everyday it will not malfunction.
> If I do not use the rig for two or three weeks problem gets very
> bad.
> Seems that I get only the RF output that the final bias of 50ma
> would give
> me.
> I get no grid and only 50ma on the meter.
> I can hear the relay kick in but I hear no load on the transformer.
> The only way I can get RF output is to tap ever so gently on the
> carrier
> generator board or the mixer-bandpass board.
> And, when I say it only takes a gentle tap I mean it.
> Once I get radio to work it puts out full power and no more
> problems.
> If it sits for more than a day I have to do the tap again or if no
> longer
> than a day the pushing of the mike several times to activate
> vibrations from
> the relay causes the unit to come to life.
> If I turn up the driver control all the way when I click the mike on
> and off
> makes this fix work faster.
> I do not think this could be a resistor or capacitor problem since
> the
> symptoms go away completely once the unit works.
> I have checked for bad solder joints and have found non.
> I have replaced tubes and problem pops up again.
> Can anyone come up with any ideas?
> Thanks,
> Dan
>
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