Heathkit diode 57-27 and the ALC circuit.

[Chuck W4MIL]

Ken,

The 57-27 cross references to the NTE 116.  It so happens, the 1N4001 
also cross references to the NTE 116.

57-27 = 1N4001  (based on NTE's data)

Hope this helps.

73 de W4MIL
Chuck



-----Original Message-----
From: kgordon2006 at VERIZON.NET
To: HEATH at LISTSERV.TEMPE.GOV
Sent: Sat, 3 Mar 2007 2:45 PM
Subject: [HEATH-TEMPE] Heathkit diode 57-27 and the ALC circuit.

  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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