[Amps] Super Cathode Driven Tetrodes

[Carl]

----- Original Message ----- 
From: "Jim Thomson" <jim.thom at telus.net>
To: "Carl" <km1h at jeremy.qozzy.com>; <amps at contesting.com>
Sent: Saturday, October 27, 2018 3:51 PM
Subject: Re: [Amps] Super Cathode Driven Tetrodes


> <That seems very low drive for passive grid. The NCL-2000 could use up to
> <100W in the high drive positon at 50 Ohms and 20-25W into the low drive 
> 100
> <Ohm configuration.
>
> <Carl
>
> ##  NCL-2000  didnt use a 4CX-1500.   He used bird wattmeters on both 
> sides of the hb  4CX-1500B.   10 watts for 1.5 kw on low bands
> and  20 watts on upper HF bands.  Dunno how much  B+  and screen voltage 
> used.    I believe he terminated the grid with a 50 ohm globar  he
> removed from his heathkit dummy load.
>
> ## Local buddy has an Alpha  8410, with a pair of
> 4CX-1500Bs.  Dunno how much drive it requires, I will  ask him.
> He sez it does an easy 2 kw output on 80m.
>
> ##  Those  OM-4000  amps, that use  a pair of chinese FU  tetrodes,  sorta 
> their version of a
> 4CX-1500B,  only require 20-25 watts of drive for  4+  kw output...per the 
> folks I know that own them.
> A fellow in Colorado I know, just bought the manual tune version of the 
> OM-4000.  Input attenuator removed,and an easy 5 kw out.
> They removed the  FCC  approved input attenuator, or bypass the 
> attenuator. Then they end up with the
> same version OM-4000  as the rest of the planet gets.
>
> ##  Remember that  tetrode that Rich built ?   He used a  surplus  500 ohm 
> globar and a 1:9  trifilar .  20 db gain.   Ideally,
> a  450 ohm globar is used.  Then a small amount of uh in parallel with the 
> globar, to cancel out the tubes stray input  C /  XC.
>
> ##  Im not a grid driven tetrode  expert, with minimal experience, except 
> for the G2DAF  congig..... which I would not recommend to anyone.
>
> Jim   VE7RF


  The 4CX1000A/1500B and the FU's are all high gain tetrodes that take very 
little drive in AB1 swamped grid driiven. When almost no POWER was required 
they, the 8122, and other similar tetrodes were about equal in that 
respect..

My NCL-2006 conversion uses a tuned circuit for impedance step up to the 
grid and a 50 Ohm resistor at the input and easily does 1300W with 12W drive 
from the transverter.

The 4CX's were used in a few commercial/military TX and plain grid driven 
using receiver type tubes. Others used a loafing 4CX300A or 8122 in either 
cathode drive or swamped grid where quick QSY was needed.

Carl. 


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