>Subject: [AMPS] SB1000 grid current
>Sent: 4/04/1997 5:17 AM
>Received: 4/04/1997 8:37 AM
>From: Chris Pedder, g3vbl@netcomuk.co.uk
>To: amps@contesting.com
>
>Hi,
>
>Although I seldom if ever use it, I do keep an Heathkit SB1000 amp. Having
>fitted a soft (=step) start I am no longer troubled by the incredible thump
>that I used to get at switch on but am puzzled by the following on page 66
>of the manual:
>
>12. Apply only enough drive to indicate either 1000 watts of output power,
> or 200ma of grid current.
1000W of output from a single 3-500z at 3000v is downtown
Distortionville, Chris. However, at 4000v, not. The max. anode current
spec. for linear amplifier service is 400mA DESPITE the manual's
technoblather. At 3kV, 400MA is 1200w in. The output should be about
60% of that.(720w) .
>The figure of 200ma of grid current appears to be at odds with Eimac specs.
>Is there anyone who can comment on this?
Eimac does not have a max. grid current spec. for the 3-500z. By
underloading, you can peg the grid current meter in most amps, but
nothing seems to fail--but to do the peg out trick, only a trickle of RF
makes it to the antenna, which is hardly why we buy amplifiers. Tune for
max. RF output and the grid current will be just fine, every time.
I haven't seen anything were Eimac discuss adjusting for a specified
grid current in a g-g amplifier tube. .
The only kind of linear amplifier that needs adjustment of grid current
is Class AB1--wherein one adjusts current for virtual zero. .
Rich---
R. L. Measures, 805-386-3734, AG6K
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