Globe 350 Re: [AMRadio] 4-65's

RJ Mattson rjmattson at
Thu Apr 5 20:46:10 EDT 2007

Hi Jim
I am always looking for substitutes for my Champs AX9909's.
The top of the list are two 5894's with the plates wired in parallel. I 
believe there was a article in ER with is conversion?
How did you get the HV up to 1500v?
Would an additional fil xmfr resolve cathode modulation or could a DC fil 
ckt and cap decoupling be the solution?
I have a stock of both 4-65s and 5894/7854s

----- Original Message ----- 
From: "Jim Candela" <jcandela at>
Subject: Re: [AMRadio] 4-65's


   I used a pair of 4-65's in a Globe Champion 350 conversion from AX9909's. 
This was kind of tricky to do, but since I had the tubes, and the sockets 
were the same, i gave it a try.

Some recollections from that conversion:

The 4-65 is a Higher voltage, and lower current tube. In class C service, 
the efficiency is really great at 3kv plate voltage, and is diminished at 
lower voltages.

Used 4-65's like a lot of thoriated tungsten tubes have a filament that is 
very brittle, and therefore shipping them is risky since the filament might 
be rattling around when you take them out of the box. The 304 TL is also a 
good example of this.

In the Globe 350, with a beefed up plate supply (~ 1500v instead of 1000), I 
could easily run 500 watts DC input at about 80% efficiency, The in/out 
ratio was pretty constant from 160-10m. The tubes had little color. The only 
fly in this conversion was that I wired the two tube filaments in series to 
use the existing 12 volts AC for the 9909's. This resulted in some 60 hz 
cathode modulation making the rig sound like a BC-610 running on the 
internal VFO.


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