[Amps] Additional comments, re GU-74B/4CX800A

[Jim Thomson]

Date: Fri, 26 Oct 2012 09:42:01 -0400
From: "Carl" <km1h at jeremy.mv.com>
To: "Jim Garland" <4cx250b at muohio.edu>, "'Leigh Turner'"
<invertech at frontierisp.net.au>, <amps at contesting.com>
Subject: Re: [Amps] Additional comments, re GU-74B/4CX800A


Sell them for a nice profit and start over (-;

Carl
KM1H

## absolutely brilliant idea Carl !   Then buy a real tube, like a 3CX-3000A7. 
Where 100-150 ma of idle current will net you –59db pep  of IMD3..and that’s
at 5+ kw pep out. 
. 
50w in= 1.5 kw out.  100w in= 2.5 kw  out    150w in = 3.5 kw out 
200w in = 5.2 kw out.

What more do you want ?   The 225 watt CCS  grid diss is actually way more, once the grid
is bonded to the chassis in GG.  You can use it as a dummy load for your  xcvr.   The grid in that
tube is impossible to blow up, can’t be done.   A simple, fast 1A 3agc fuse on rear panel, wired between
chassis and neg terminal of grid meter is all you need for grid protection. Fuse blows , and no more path
for dc grid current.  Amp can’t be driven.  PO drops to zero..asap.   Input swr rises to infinity. Xcvr shuts down
real simple, why over complicate things, with ebs, neutralization, screen supplies, and having to cancel out the
xc of the tube on each band, pita. 

EBS will work, sorta....and esp if PTT is used.  On SSB VOX, it really buys you nothing.  None of em are fast
enough to cut off between syllables.   They are fast enough to cut off between words though..which saves  a little bit of
power.  Once the vox drops out, its cut off  anyway.   Ebs won’t work at all in  ESSB mode.. unless you slow down the
decay on the ebs... which then renders it useless. 

If you could pick any tube u wanted.... nobody would pick a GU-74B.   Other than its cheap price, 15 yrs ago,
it has nothing going for it. 

Jim  VE7RF