On Jun 26, 2006, at 8:48 AM, Allen Jones wrote:
> I have a Heatkit SB-230 amp and would like to add
> protection for the grid. I'm not an engineer but it
> looks like a simple transistor switch with a latching
> relay will not suffice as it would be difficult to
> develop the 0.6 to 0.7 VDC needed with the low amount
> of grid current that normally flows in the metering
> circuit. Eimac specs the tube at 30ma max.
The spec is 5w max.
>
> I was told to use a circuit similar to the one in the
> Ameritron AL-800 or 1200 which uses an op amp. The
> manuals are available on the Ameritron site but do not
> contain schematics. Any suggestions or assistance
> will be much appreciated.
Grid fusing can be accomplished by putting a 20 to 39-ohm, 1/4w
carbon film R - or a fast-acting 1/10a fuse - in series with the grid-
I meter shunt. Additionally, a 30v to 50v transient V suppressor
should be connected across the fusing element, back to belly 3a
diodes should be paralleled with the meter movement, and a glitch R
added in series with the HV+ lead.
If it was my amp I would add a VHF suppressor to improve stability.
>
> Allen, W9DZ
>
>
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R L MEASURES, AG6K. 805-386-3734
r@somis.org
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