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RE: [BULK] - [Amps] Mod thunderbolt to 4CX800A

To: 'Bob Good' <>,
Subject: RE: [BULK] - [Amps] Mod thunderbolt to 4CX800A
From: Steve Katz <>
Date: Wed, 17 Nov 2004 14:23:03 -0800
List-post: <>

I would appreciate comments on the feasibility of modifying an old Johnson
Thunderbolt Amp (4-400A's , tuned /  swamped input) to use 4CX800A's.  In
doing so, I would also desire to include 160 meters.  Care nothing about
useage above 20 meters.  I would expect to add fixed inductance to the
roller inductor, change or add to the plate RFC, add caps to plate tuning
and loading, modify input bandswitching for 160 meters, adjust screen / grid
parameters.  Will use only on 230vac. Continue to use tuned input.
Does the P/S have enough plate current capacity? 

::Not for me, it doesn't.  It's only a 2000Vdc 500mA power supply.  So, that
should be enough to run 1kWdc input and ~600W output, which is what the
T-bolt safely ran as designed.  The plate tank components, including the
roller inductor, really aren't good for more than that, anyway.

::My thought, as a T-bolt owner: Waste of a very large and heavy amplifier
that doesn't run much power to do such a conversion, other than as a science
project.  A "mint" unmodified T-bolt without any changes is worth more to an
EFJ collector than it is as an amplifier.  I'd sell it and buy an amp that
already covers 160, and is smaller, lighter and grounded-grid.  A kW PEP
output amp doesn't have to weigh over 120 lbs nowadays...  -WB2WIK/6

 Is the cooling adaquate?  How about including most desirable QSK from
available kits?  I've also seen kits for inrush and grid protection, etc.
Exciter will be Omni VI.  Thanks to Amps for posting and to all who reply.
Regards,  Bob K4BG
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