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[Amps] Amp output power

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Subject: [Amps] Amp output power
From: "Jim Thomson" <>
Date: Wed, 26 Aug 2015 00:32:18 -0700
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Date: Mon, 24 Aug 2015 22:31:06 +0100
From: Steve Thompson <>
Subject: Re: [Amps] Amp output power

If you check at

there's several data sheets. I came across a copy of the one with 
1370W output spec. and copied it to David to host. I believe there 
was a spell where FCC applied rules relating to output power spec. 
of the devices in a transmitter, hence the 750W rating appearing 
so a pair was valid for a 1500W amplifier.

I think the same applied in the case of Svetlana 4CX800A data.


##  u are correct.    Right after the FCC changed the regs  and went  from
1 kw dc average input  ( 2 kw pep input)   to 1.5 kw pep output,  Eimac
immediately  down graded the specs on the 3CX-800A7.   The idea of 
course was to make 2 x tubes  look normal for a 1.5 kw pep out amp. 

##  the pulse rated version of the tube is what Eimac recommends   for 
FM broadcast use..esp in foreign countries where the line voltage fluctuates
all over the map.   Too many tubes were blown up from excessive B+. 
The pulse rated version is good for 3.5 kv. 

##  a single pulse rated  3CPX-800A7 tube works good in stuff like the 
dentron MLA-2500 amps.    The chinese 8877 is a superb tube... but may well
be difficult to retrofit in a lot of table top amps, not enough space and 

##  Dunno why alpha  has always used a silly tube line up in its amps over the 
Their current amp with the 2 x 4CX-1000s  is yet another example.   A single 
would easily have done the job.   No screen supply required..and a simple 
Two breechblock 4CX-1000 sockets, gimme a break.   Alpha should just have made
two identical amps, one auto tune and the other a manual tune..and both using 
the same 
B+ supply and same single 8877 tube. 

Jim  VE7RF 
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