[Morrow] Morrow MB 565 transmitter modulator

[John King]

My very nice MB 565 has a peculiar modulator tube problem.

The transmitter works well as well as the modulator EXCEPT when I set the bias 
on the two 6AU5 GT modulator tubes to the  resting modulation current of 40. ma. 
with the  microphone PTT keyed as recommended in the manual, the two tubes begin 
glowing RED. 


It may be that the meter shunt for modulator current has changed thus when the 
transmitter is keyed, the modulator tubes are drawing much more that the 40 ma, 
indicated on the panel meter and turning RED because of excessive resting 
current when keyed up. The modulation sounds GREAT with no distortion or buzz or 
hum even with the modulator tubes turning red.

I am using the Morrow RTS 600 power supply to power the MB565 and MB6 receiver.

I might try and substitute an outboard meter  or use a VOM in the current 
position to check the accuracy of the Morrow inboard meter.

When modulated, the power output increases by about 300% and sounds OK.

Your experience with the Morrow MB transmitters will be appreciated. The 
modulator is in 

AB1. Thanks for reading and responding. 73, John, K5PGW