Heathkit diode 57-27 and the ALC circuit.

[Stu Lyon]

I would recommend the 1N5711 Schottkey designed for BalMod and AGC work.
See:  http://www.mouser.com/search/refine.aspx?Ntt=511-1N5711%09   
and   http://www.st.com/stonline/books/pdf/docs/3238.pdf

Haven't we had this discussion before?

73, Stu W6CUX

Kenneth G. Gordon 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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