Date: Mon, 1 Apr 2019 13:34:48 -0600
From: Steve London <n2icarrl@gmail.com>
To: amps@contesting.com, km1h@jeremy.qozzy.com
Subject: Re: [Amps] QRO 2500DX MARK lll 4CX800
<So, Carl, where would you suggest us cheap, constantly crying, hams get new,
or
<at least new-old-stock Eimac 4CX800's and 3CX800's ? Lotsa luck.
<73,
<Steve, N2IC
## Eimac NEVER produced a ... 4CX-800 !! Its not in any of their
catalogs, never was, still isnt.
The tube in question is a SURPLUS Russian tube called a ... GU-74B. US
hams are not gonna buy
an amp with a ...GU-74B in it. So they re-labeled the tube, and called it a
... 4CX-800..... and also came up with bs
new specs.
## Of course hams thought that the...Russian 4CX-800 was a clone of an Eimac
tube.
In actuality its a surplus russian tube..with 600 w of anode diss, and lousy
imd. To get
half decent imd from those tubes, they have increased the idle current through
the roof.
225 ma PER tube is crazy. Thats 450 ma for a 2 holer..and 675 ma for the 3
holer.
## Emtrons .... fix for the sky high idle current was to use EBS..electronic
bias..which sorta works
between words, but not between syllables. Emtron has since gone tu.
## 3CX-800A7s are used in single tube and also 2 holer configs in FM
broadcast. Eimac
came out with a warning for FM broadcasters to use the 3CPX-800A7 instead.
The 3CPX-800A7
is the pulse rated version, and will handle a lot higher B+...like 3600 vdc.
The issue was, in some foreign countries,
the incoming line voltage was all over the map..that plus spikes,
transients, surges etc, would flash over between
anode to grnded grid. The pulse rated version solves that issue, however,
the grid current is typ 10 ma higher, non issue.
Jim VE7RF
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