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[AMPS] Amps in Sept QST

To: <amps@contesting.com>
Subject: [AMPS] Amps in Sept QST
From: km1h@juno.com (km1h @ juno.com)
Date: Tue, 26 Aug 1997 19:28:37 EDT
On Tue, 26 Aug 97 15:27:48 -0800 Rich Measures <measures@vc.net> writes:
>>The Product Reviews of the Alpha 91b and the QRO 2500DX merit reading
>>since these are the first with the Svetlana 4CX800/GU-74B tetrodes.
>>To be honest, I am amazed at the IMD performance of both amps; the 
>Alpha
>>is 45/49 dB and the QRO is 43/40 db for 3rd/5th orders. This sure 
>beats
>>the old 25/28 dB typical of 4CX250's.
>>
>That's probably better IMD performance than any transceiver, Carl.  
>However, a 4CX250B with 10 ohms of cathode RF negative feedback R, 
>loaded 
>to 5mA of screen current, has IMD performance that is comparable to 
>the 
>typical transceiver.  

Unfortunately most 4CX250 sockets have the cathode pin internally
grounded to the mounting ring precluding any changes. 

>...snip....
>>
>>Of particular interest is that all 3 amps experienced failures during
>>testing which IMO is a bit bizarre. 
>
>Bizarre by far.   What was the reported nature of the failures, Carl?  

Alpha had a screen circuit ( not tube) problem, QRO blew a 4:1 output
matching toroid and Ameritron had an unexplained large increase in IMD.  
The amps were replaced and testing resumed. 

SNIP

73...Carl   KM1H

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