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[Amps] parasitic suppressor for six meters

To: "Amps group" <>
Subject: [Amps] parasitic suppressor for six meters
From: "Jim Garland" <>
Date: Thu, 12 Jul 2018 16:24:39 -0600
List-post: <>
About fifteen  years ago, I rebuilt a junker Alpha 76  (no tubes,
flashed-over bandswitch, burned plates on tuning cap, burned plate choke,
other problems) and converted it to a six meter monoband amplifier. I
replaced the pair of 3CX400s with a single 3CX800A7, installed vacuum T/R
relays, and redid the metering and front panel switching. You can see it at


I've used the amp for years, with about 750W output, but recently ran into a
power supply problem and had to tear into it. In doing so, I noticed the
parasitic suppressor was burned.  I believe it's probably the original
suppressor, and it consists of 1.5  turns of 12AWG tinned wire shunted by
two 51 ohm two watt resistors, one of which was burned in half. The amp has
never had parasitic oscillations to my knowledge, so I'm guessing there was
probably a bit too much inductance in the parasitic inductor. I'm thinking
about replacing the two burned resistors with a single 22 ohm 5 Watt metal
film resistor, and trimming the inductor to a single turn. Does this seem a
reasonable change? Does the tube require any parasitic suppressor at all?


Jim W8ZR

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