----- Original Message -----
From: "Jim Thomson" <jim.thom@telus.net>
To: "Carl" <km1h@jeremy.qozzy.com>; <amps@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 8410 is power limited to keep the FCC happy.
I guess they got a bit peeved when so many 8K's went to hams!
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