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Subject: [AMPS] 4-1000 IDLING CURRENT
From: (David E Sinclair)
Date: Sun, 29 Mar 1998 01:50:50 -0500
Bob- You may have some measurement error with your plate
voltage or plate current readings. The figures you give of 4200V
and 450mA under load with 1450 watts out works out to nearly
77% efficiency. (1890 watts plate input) Perhaps you are tuning
into a greater than 1:1 SWR and forgetting that your net output
power would be the difference between foreward watts and
reflected watts? Wattmeters are nototiously inaccurate anyway.
77% sounds pretty darn good to me!  Not impossible, but some-
where around 50-60% is what I would expect.
Are you running the tube with or without a tuned input network?
It will be harder to drive without the network, and power
output may be less than what is possible with the network.
I'm not sure about the correct idling plate current, but I think I
remember someone on the reflector mentioning about 20mA
per kilovolt, which would put you in the ballpark.
You shouldn't have much problem driving it with 200 watts, even
without a tuned input. I'm not sure what you mean about the 
group of 3 tubes working the same in your amp and developing
"full output in another amp." It may not be a fair comparison due
to differences in input tuning networks, output tuning networks
plate VI relationships, etc. Are you really sure there is a problem
here?  73, David K3KY
 David Sinclair         K3KY

On Sat, 28 Mar 1998 20:16:13 EST K8MLM <> writes:
>My Home brew 4-1000 amplifier works great except for on thing.  The 
>power out
>seems low.  I believe it may have something to do with the low idling 
>Plate voltage is 4,600 VDC and idling current is about 80 ma.  The max 
>current I can load it to is 450 - 500 ma.  At 4,200 VDC under load and 
>450 ma
>plate current, gets 1,450 watts out with about 130 watts drive.  Have 
>the B- line for stray resistance; none.  Have tried it with the zener 
>both in
>and out; no difference.  Power supply is capable of more than enough 
>and I have 200 watts available.  I have 3 tubes: all 3 operate the 
>same in my
>amplifier, full output in another amp.
>Any suggestions!
>Thanks, Bob
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