Heathkit diode 57-27 and the ALC circuit.

[Alex [Temple-Heath List]]

Hi Ken

The 57-27 diode crosses to the following substitutes, and is 
basically a 1 amp 600V rectifier diode. Any generic silicon diode 
with those specs should work.

57-27: 1N2071, 1N4005, 1N5397 (600 PIV 1A Rectifier).

The 1N400x series diodes (1N4005 = 600V, 1N4007 = 1KV) are both very 
easy to find and will of course fit the job.

Hope that helps.
-Alex

At 03:45 PM 3/3/2007, you wrote:
>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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