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Re: [Amps] 3CX3000A7 on 144 MHz

To: Amps <>
Subject: Re: [Amps] 3CX3000A7 on 144 MHz
From: Roger Parsons via Amps <>
Reply-to: Roger Parsons <>
Date: Sat, 8 Feb 2020 01:15:57 +0000 (UTC)
List-post: <>
Jim w8zr wrote:

"Seems to me this problem may  not be so troublesome......"

I have to agree with Jim on this, for various reasons:

There is no reason why a DC filament supply should not be centre tapped, most 
simply with a resistive bridge;

The bias on the tube is related to the average of the emission over the whole 
of the filament, and this is static with a DC filament supply;

Those of us who are old enough will remember battery tubes (such as the 1T4 and 
many others). These (obviously) had a DC filament, and significantly an HT 
voltage which was sometimes as low as 22.5V. Any problems due to a voltage 
gradient along the filament would likely be much worse than with a power tube 
with several kV on the plate. Yet they worked;

And most significantly. I cannot find any recommendation by Eimac or other tube 
manufacturers against using DC filament supplies. This is despite their 
specifications going into great detail about other matters such as permissible 
filament voltage variation. 

73 Roger
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