Heathkit diode 57-27 and the ALC circuit.

[Kenneth G. Gordon]

Does anyone know what type of diode the Heathkit part number 57-27  
is, and what its ratings are? PIV, current, etc?

I know it is a silicon diode, but that is as much as I can find out about it.

Three of these are used in the HW/SB transceivers in the ALC circuit. I 
think at least one of mine is damaged as I have no ALC action at all in 
any SSB mode. 

When I adjust the MIC/CW LEVEL control on CW with the key down, 
and with the meter in the ALC position, I can swing the meter from 
somewhat below 0 to full-scale, depending on where I set the control, 
but nothing whatever shows up on the meter when in voice mode, 
except an occasional blip upwards from zero on very strong voice 
peaks.

I have checked the settings of the MIC/CW LEVEL control on voice with 
a scope and on air, and the settings are proper for best power output 
and voice quality, but there is no ALC indication.

I found a short circuit from the screen voltage connection to one of the 
diodes under the final amps yesterday, so I think at least one of the 
diodes is blown.

Thanks,

Ken Gordon W7EKB

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