[Amps] Zener Bias Replacement

[Marv Gonsior]

>I've been following this string with a great deal of interest as 
>some years ago, W6GNX and I made bias measurements on three 
>different legal limit 8877 amps.  Two were home brew and one was a 
>Henry 3K Classic X.  All were measured up to 1A of anode 
>current.  We no longer have the data but the diode strings were by 
>far the worst regulators as compared to a Zener and a simple 
>transistor regulator.  The developed 12V from the diode string 
>continuously rose with the current like a rubber band and, obviously 
>as now a number of inputs have shown, the t.c. is part of the 
>problem let alone having ~20 diodes to assemble for an 8877.  The 
>suggestion of two 6V Zeners seems like a very good choice.

In my case, with the two different 8877 amps, the Henry was pretty 
bad and it used a  Semtech diode pack (replaced with a 50W Zener on a 
good heat sink) and the rise was in the order of several volts at 
peak anode current.  Obviously, this leads to current and power 
limiting and IMD generation.  In my opinion the diode string is the 
worst thing one could do for biasing!  In a number of times, in the 
past. when I have read where someone extolled the virtues of doing 
this, I have written and asked for a measurement but never had a 
reply.  I have to wonder why.  It is refreshing to see the current 
interest in this area and it would be a real benefit to all to see 
some additional, meaningful measurement data being published.

>73,
>
>Marv, W6FR