SB401 Problem Help Please

[Dan Pividal N4VET]

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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