[ARC5] Fwd: HP 23 for ARC5

[Rich Post]

From: Rich Post <kb8tad at gmail.com>
Date: Mon, Feb 24, 2025 at 11:35 PM
Subject: Re: [ARC5] HP 23 for ARC5
To: Russ Tine <rtalfa at yahoo.com>

No need for a voltage divider.  Just add some regulation to the lower B+.
Back in 2016, I did something similar with a BC-696A and an ARC-5/T22.  The
HP-20 is the forerunner of the HP-23 series.  The published highest
voltages are different mostly because the HP-20 shows loaded voltage and
the HP-23 unloaded, but the power transformers are nearly identical.  The
highest voltage is obviously for the plates, but a lower B+ is available in
both.  Limiting the screen voltage is important.  I used a pair of recycled
high-voltage N-channel FETS as regulators for the lower B+ available in
both power supply models. The FETS were recycled from computer power
supplies. According to the data sheets, the junk box pieces showed that a
W9NA80 was rated at 800 volts and 8 amps, and a Toshiba K2746 at 800 volts
and 7 amps. The regulated voltage was fed the oscillator at about 200 volts
and the screens of the 1625 pair at about 270 volts.  One of the
transmitters had already been converted to 12 volts filament and the other
was still 24 volts for which I used a pair of gel cells to keep it original
but another 12 volt transformer could be added in series aiding.

I was able to mount the regulators right inside the HP-20, but an outboard
chassis would work as well. Since the keying relay was absent in both
transmitters, I also rigged up a simple QSK box with a pair of recycled
relays, a DPST and an SPST, in series-sequential-action to first trigger
the regulated 200 volts to the oscillator and the coil of the other relay
which in turn triggered the cathodes, solving both a chirp in the signal
and the open voltage on the key.

Restoration details and powered results were written up in a pair of
articles in "The Spectrum Monitor" magazine for the December 2015 and
January 2016 issues available as back issues, cheap from the publisher.


I will try to attach the simple schematics of the regulation circuit and
the sequential keying relay "QSK box".

Rich KB8TAD
[image: Figure 15.JPG]
[image: Figure 13. .jpg]



On Mon, Feb 24, 2025 at 12:20 PM Russ Tine via ARC5 <arc5 at mailman.qth.net>
wrote:

> Hi Folks,
>
> I'm new to the list, and I am looking for some advice about using an HP 23
> power supply for my T-22.
>
> I still use the power supply for my HW 101, so I do not want to make any
> mods to the PS itself, I would rather add a voltage divider external to the
> PS that I could plug in for the T-22 and remove for the HP 23.
>
> Thanks in advance and 73,
>
> Russ Tine K1RWT
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