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More rugged screen and grid structure for high vibration ( read military ).
Don W4DNR
Quoting Colin Lamb <k7fm@teleport.com>:
 And, just to complicate things a bit, the 4CX250R is stated to  
provide more output than the 4CX250B.  I think it is rated for  
repeater usage, although the bias and characteristics are different  
than the 4CX250B.
73,  Colin  K7FM
On 12/28/2014 1:34 PM, Fuqua, Bill L wrote:
   I suspect when EIMAC came out with the 7034 they wanted to  
suggest that they were a good replacement for the
4X150A. Military particularly wanted to use the same part number  
when replacing tubes in their radios, and I suspect that
EIMAC wanted to not only promote the 7034 they wanted to make one  
tube type rather than 2.
  There are subtle differences between the two tubes, besides plate  
dissipation limit. The characteristic curves for the 4X150A does  
not show any
area where there is a negative flow of screen current, while this  
is an obvious issue some times with the 7034 and 4CX250B.
This could be a problem in some cases when interchanging these  
tubes. There are other differences, one is that
when operating the 7034 at 500MHz it does produce the same output  
power but requires 1/3 the drive power.
 73
Bill wa4lav
 ________________________________________
From: Amps [amps-bounces@contesting.com] on behalf of Colin Lamb  
[k7fm@teleport.com] 
Sent: Sunday, December 28, 2014 8:15 AM
To: Peter Voelpel; amps@contesting.com
Subject: Re: [Amps] Power from Pair of Eimac 4 x 150 a / 7034?
"The Eimac data sheet does not confirm that
http://www.r-type.org/pdfs/4x150a.pdf
The RCA 4X150A/7034 data does:
http://pdf1.alldatasheet.com/datasheet-pdf/view/241849/ETC/7034-4X150A.html"
The RCA data sheet refers to a 4X150A only, which is a different  
tube than the 4X150A/7034. 
73,  Colin  K7FM
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