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Re: [Amps] Replace 2x 4-400 with 2x 3-500ZG

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Subject: Re: [Amps] Replace 2x 4-400 with 2x 3-500ZG
From: "Peter Voelpel" <>
Date: Fri, 2 Jun 2006 12:25:16 +0200
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I usually do it the other way round as 4-400G/QB4/1100/RS1002A are more
rugged then 3-500Z.
You will get higher amplification, so perhaps 20% more output with the same
driving power by using 3-500Z.
But with enough drive I prefer the tetrodes.
I can do 2,3KW output or even more with the pair of RS1002A in my L4B at
4KV, with stiff 3KV they provide 1,8KW at 120W drive and 1,5KW when using
the original power supply (made for 60Hz). My homebrew P/S is 3-phase.
The weak point is the bandswitch, it has to be cooled on the high bands, I
use a good size CPU fan there. If you run a commercial amp that will be no

Peter, DF3KV

-----Original Message-----
From: [] On
Behalf Of Posselt Werner
Sent: Freitag, 2. Juni 2006 10:26
Subject: [Amps] Replace 2x 4-400 with 2x 3-500ZG


Is it possible to swap the 4-400s with two 3-500ZG without any further
The tubes are operating in grounded Grid configuration.
The HV supply is homemade delivering 3,3KV.
How much increase in power output can I expect?

Thanks for your answers!

73, Werner
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