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

Subject: Re: [Amps] Replace 2x 4-400 with 2x 3-500ZG
From: Joe Isabella <>
Reply-to: Joe Isabella <>
Date: Fri, 2 Jun 2006 06:47:59 -0700 (PDT)
List-post: <>
I don't know...  My Henry 3K-A puts almost 4kV @ ~1A on my RF Parts 3-500ZGs, 
and I beat the tar out of 'em.  They'll do 2.4kW output with 150W or so of 
drive.  I run them with about 80W or so drive for legal limit.  100W will do 
almost 2kW out.  I also run them on AM @ 350-400W carrier (still about 1500W 
PEP) and they take that abuse in stride (turning quite orange on the occasional 
long-winded AM transmissions).  :-)
Been running that way for several years now with no signs of stress -- still 
plenty o' power!!  The upgraded blower I put in helped, but I had to move the 
amp across the room because of blower noise.
Joe, N3JI

----- Original Message ----
From: Peter Voelpel <>
Sent: Friday, June 2, 2006 5:25:16 AM
Subject: Re: [Amps] Replace 2x 4-400 with 2x 3-500ZG

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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