[Amps] The dilemma of Tx tube

[Jim Thomson]

Date: Wed, 1 Aug 2012 19:37:39 -0500
From: Rob Atkinson <ranchorobbo at gmail.com>
Subject: Re: [Amps] The dilemma of Tx tube

The eimac triode connected g.g. cathode driven data sheet for the 4x1
has specifications for 3, 4 and 5 KV.

Rob
K5UJ

On Wed, Aug 1, 2012 at 4:07 PM, <Gudguyham at aol.com> wrote:
>
> If I am not mistaken, the 4X1 "typical" GG service is rated at 3KV. Pump
> it up with the proverbial "pole pig" power supply at 6KV and something has
> to go out of spec. Most likely IMD?


##  If you looked at any Eimac catalog  from the  1960-1995,  you WON’T 
see  any GG  specs for a 4-1000.  I mean with screen + grid  bonded to chassis, and
run as a high MU triode.    Einac did list some GG  specs for hams  
in the odd rag  like CQ  once in a while... like for 3-4-5 kv.   That was just a courtesy 
thing.  No ham was gonna buy a brand new Eimac 4—1000 anytime soon.  For less  money,
you could buy a NEW 3-1000Z.... which IS   rated for GG, and also rated up to 6 kv in GG.  

##  Fact is the IMD sucks on the 4-1000.     A   160m, monoband single 4-1000 in GG was featured
in  the ARRL handbook in the 80’s... and with just 900w pep out, the IMD was horrible on it! 
-30 db pep for IMD3.   The 5-7-9-11-13 hardly drops at all on the arrl lab 2 tone test setup, as depicted
in the handbook article.  

##  I had several of em myself.  The last one ran  4800 vdc no load, and  4400 vdc under load. 
120 watts of drive and  tuned input used for each band.  Output was 1900 w pep.   I lucked
out, and obtained 2-3  brand new Eimac 4-1000’s.  A broadcast eng buddy of mine sent a few
my way, sealed in the box’s... and only built 2-3 months  before I got em.   They were used,
4 at a time in some AM  broadcast TX’s.   2 in parallel for the RF deck,  and  2 more in PP, in the
modulator.   That’s  why you will see  the  odd ball fil xfmr in dahl’s  commercial catalogs. 
208 or 240 vac   single phase input..... and  4 x separate secondary’s,  each sec  was  7.5 vac @ 21 A  CCS. 

##  Even with only 4400 vdc on the tube under load, and brand new tube used, the imd at 1900w
pep out was not spectacular.   It didn’t help that the Drake T4XC and also drake  TR4 used to drive it
was only  -30 db pep  for IMD3.    -24 db below one tone, typ of the sweep tubes used by drake. 

##  NO tube maker will endorse  tetrodes used as high mu  GG triodes  anyway.  In most cases, the
control grid hogs most of the .....“grid current”  and the  control grid  diss  is exceeded. 
4-1000 only has 25 w of grid diss   vs the  50 w grid in the  3-1000Z  

##  Several  folks also tried and used 4CX-5000’s  in GG, with screen + grid  grnded to chassis, then
run as a GG triode.   Typ was to drive it with a SB-220, in the CW position, with 600w  of drive.
7.5 kw pep out  with lousy imd, but nobody cared abt imd back then in any 4-1000 amp. If you
had one... or a 2 holer, you were the kingpin in your town...and not to be trifled with.   And yes, mine
had a window in it.  Local’s  would stare in awe at it, running cherry red and orange.  No different
than muscle cars.  Legal limit was for somebody else...still is.  

Jim  VE7RF