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.
FYI: http://www.w8ji.com/neutralizing__amplifier.htm
GL, de Han JE1BMJ QM05BR
-----Original Message-----
From: Jim Thomson
Sent: Thursday, March 26, 2015 3:59 PM
To: amps@contesting.com
Subject: [Amps] 3CX1200 tubes
Date: Sat, 21 Mar 2015 07:30:20 -0700
From: "Randy" <hamradio@oz.net>
To: <amps@contesting.com>
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?
Thanks.
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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