Date: Tue, 03 Feb 2015 13:36:23 +0000
From: Manfred Mornhinweg <manfred@ludens.cl>
To: amps@contesting.com
Subject: Re: [Amps] Need Zener for 2KD-3
This solution has a more stable voltage than a series string of diodes, uses
fewer components, and doesn't need any extra support, because the two small
parts are simply soldered to the transistor, which is bolted to the chassis or
a
heat sink. It's also suited to replace higher voltage zeners, which is
impractical using diode strings.
Manfred
## Your small zerner + transistor will work, I have used it myself.
A string of diodes like 1N5408 or 6A10 will also work, and are bomb
proof. High power 50 watt zeners are a pita..and run too hot imo.
Come glitch time, hiccup time etc, etc, they will fail shorted on you.
## A 6A10 is rated for 6A CCS, and a 400A surge. Nobody ever blew
a string of 6A10s out , when used for GG bias service. The V regulation
is plenty good enough. Put a 10,000+ uf cap across the entire string, and it
wont
budge. If u have an application where you require say 30-40 volts of bias,
and
cathode currents of 3-4 amps, a string of 6A10s works just fine. Cathode
current
of course being the sum of plate + grid current. 30+ volts with 2+ amps of
cathode
current will cook a small zener + pnp transistor setup. You would require a
big heatsink to
dump the 60-160 watts of heat. Strings of diodes don’t require a heatsink.
## If u really want to go over board, you can also parallel 6A10s..and the
current always
divides 50-50 or 49-51 in the worse case. You also end up with an 800A
surge rating.
## henry radio used strings of diodes, encased in a block, sorta like a k2aw
rectifier block,
for bias on both their 3k ultra and also 8k ultra.
## For whatever reason, when high power zeners are wired in series, the V
regulation
is not good.
## For low current, low bias voltage schemes, the small zener + pnp / npn
work just fine.
Jim VE7RF
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