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Re: [Amps] 3CX1200 tubes

To: <>
Subject: Re: [Amps] 3CX1200 tubes
From: "Han Higasa" <>
Date: Thu, 2 Apr 2015 08:45:50 +0900
List-post: <">>
hi Randy san

3CX1200A7 and -D7 need neutralization for stable operation on
HF and 6 m, while -Z7 runs well without neut.

Neutralization of the A7 and D7 is easy using trifiller coil on a small
ferrite toroid core such as FT-50-43 or FT-68-43 as seen in AL-1200.


GL, de Han JE1BMJ QM05BR

-----Original Message----- From: Jim Thomson
Sent: Thursday, March 26, 2015 3:59 PM
Subject: [Amps] 3CX1200 tubes

Date: Sat, 21 Mar 2015 07:30:20 -0700
From: "Randy" <>
To: <>
Subject: [Amps] 3CX1200 tubes

Aside from the physical and filament differences is there much difference in
RF performance between the 3CX1200A7, D7, and Z7 tubes?  Is one more suited
for HF SSB service (lower IMD, etc.)?  If you had all three types available
and wanted to build an HF SSB amp project from scratch, which of these would
be the best choice?


Randy, W7HR

## For a HB amp, go with the Z7 version. No socket required... just a grid flange. And WAY less C from anode to cathode. That makes a huge difference to stability. A grid flange bonded to chassis provides the lowest inductive path from grid to chassis
there is.

## Now if ameritron used a socket on their latest Z7 version, they have it wrong. The older ameritron amps with the A7 version , neutralized the amp, cuz of the
inherent high C  from anode to cathode.

## You want to machine screw the grid flange of the Z7 directly to the chassis.

Jim   VE7RF

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