[ARC5] SCR274 improved with zener or glow tube?

[Rich Post]

Hi Jim,

As written up in my column in THE SPECTRUM MONITOR this past January,  I
modified a Heathkit HP-20 utility supply (Predecessor to the HP-23 series)
by adding a pair of high-voltage n-channel MOSFETS and a heat sink inside,
parts all recycled from dead computer power supplies.  MOSFET gate feed was
by 3 series zeners from the junk box, two at 100 volts each for the
oscillator (actually feed was195 volts for the pair) and a third zener at
75 volts for the 270 volts to the screens.  The MOSFETS were fed by the 300
volt nominal lower B+ side of the power supply which unregulated would go
from 366 to 333 volts but the 195 and 270 were rock steady from the zenered
MOSFETS.  Yes, I could have used VR tubes but wanted the whole deal inside
the HP-20.  Had to drill one new hole to attach the heat sink to the
chassis.  The 300 volt terminal was now 270 and a previously unused
terminal at the octal output jack on the HP-20 was re-labeled 195.

Since both my ham-modified 80 meter BC-696A and the 40 meter ARC-5  had had
the selector relays removed, I ended up wiring a pair of small 12 volt
junk relays from a dead UPS in series to provide the sequential keying for
the oscillator B+ and then the PA cathodes for break-in keying.  Stuck that
as a separate module inside a plastic utility box. Break in keying, no
chirp.and no bite from the key.

Fun stuff.

Rich KB8TAD

On Sat, Mar 19, 2016 at 9:35 PM, J Mcvey via ARC5 <arc5 at mailman.qth.net>
wrote:

>
> Has anyone tried a zener or glow tube to regulate the the OSC supply? Did
> it work?
> I have heard old MOPA rigs that only had a hint of chirp which is fine by
> me. How do I attain this goal?
>
> Jim, AC2EU
>
> ______________________________
>
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