[AMRadio] 4-1000A Tube question

[Mel Farrer]

Hello Paul,

I have used the 10 ohm divider to make a DC centertap on several amps 450 th etc without problems.  The gain you are getting is about typical so that is not a problem.  However, what I generally do on non zero bias tubes is not DC ground the grids, just put them at RF ground, and bias the tube appropriately.  On the 4-1000 it should not be an issue.  Check for distortion at all levels of RF and if clean, go with it.

Mel, K6KBE

--- On Sun, 2/26/12, Paul Baldock <paul at paulbaldock.com> wrote:

From: Paul Baldock <paul at paulbaldock.com>
Subject: [AMRadio] 4-1000A Tube question
To: amradio at mailman.qth.net
Date: Sunday, February 26, 2012, 4:34 PM

I'm getting close to the completion of a 4-1000A grounded grid amplifier.

The plate voltage is 4KV. I'm running  zero bias voltage. The no 
signal standing plate current is 60mA.

One unusual thing I am doing is instead of a center tapped filament 
transformer  I have two 10 Ohm resistors in series across the 
transformer "simulating" a center tap. This means there is 5 Ohms in 
series with the DC to the cathode. So at 60mA this will in fact add 
-.3V to the zero bias.

  The Eimac Newsletter FCJ-59D2 says at 4KV in grounded grid the 
standing current is typically 120mA. Is my 60mA an indication of a 
low emission tube ?

I do get a little over 10dB gain with 100W in and about 1200W out (75 
meters). The tube is of course an old, quite brown, commercial pull.

Thanks

- Paul

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