-----Original Message-----
From: amps-admin@contesting.com [mailto:amps-admin@contesting.com]On
Behalf Of Marv Gonsior
Sent: 19 July 2002 06:26
To: amps@contesting.com
Subject: [Amps] Diode Bias Strings
I would like to ask the proponents of series rectifier diode strings if
they have ever measured the developed bias between the minimum and full
power conditions? I've done it with a Henry 3K Classic X, using and 8877,
and the bias soared about 6V from zero to full signal. Read that power
limiting that must result in additional distortion products. I couldn't
wait to dump Henry's Semtec diode pack and put in a 50W,12V Zener. IMHO,
there is nothing worse than diode strings as a biasing element. Further,
just ask the G-land 6M ops what they think of the bricks that find their
way into cluttering up the band with relatively high levels of splatter
resulting from diode bias. Ian et al, are you listening?
73,
Marv, W6FR
FWIW Marv I detest those bricks almost as much as people who use 4CX250B's
with strings of zeners in the screen supply. Having tried a big 50w zener, a
string of series rectifier strings with a tap for ssb/cw and the
TL431/TIP147 combination which I used successfully at 33v @ 1.5 amps. I am
very happy with the regulator adopted by both Ian White G3SEK and Paul
Hewitt WD7S. The big zener is reasonably acceptable and my current 8877 6m
amp used this until recently and no on air complaints were received. I have
tested the TL431/TIP147 combination extensively and it is very impressive
and cost effective. I have now used it in over a dozen PA's and the results
have been excellent.
73
Conrad G0RUZ
PS on 6m I have 178 DXCC,WAC,887 grids and 1897 unique NA calls in the log
so I have been pretty active on that band.
|