Cheyene / hp-23 question

[Steve Harrison]

At 08:34 PM 3/10/99 -0500, Tom V. wrote:
>Well I was all set to use my hp-23 to power up my new cheyene, when I
>realized that the cheyene requires 600V and the hp-23 provides 800V.
>Any ideas on how to make these work together?  Thanks for reading.

Even if the Cheyenne has a 6146 (or two) in it (as do the radios that
originally used the HP23-series supplies), part of the problem may be that
its final tank circuit was designed for best operation at the lower
voltage. No-load voltage of the HP23 may be as high as 900 volts
(especially on today's high AC line voltages) and you'd have to carefully
check everything in the Cheyenne's high B+ line to make sure it can handle
at least that much. Perhaps the final's screen supply is via a dropping
resistor instead of directly from the low B+? In that case, you'd want to
change that, either the dropping resistor itself or shifting it over to the
LV B+ supply.

Then, too, look at the original low B+ requirement: is it actually what the
HP23 provides or somewhat lower (such as 200V original vs the switchable
275/350 from the HP23B, or 250/300 from the older HP23)?

And how about the bias supply? And any relays in the Cheyenne? Does the
Cheyenne have any relays running from the bias supply, and thus capable of
exceeding the HP23/23B's bias supply rating? You're probably OK on the
filament supply current requirement but it wouldn't hurt to check that out,
too.

You need to go through each and every one of these if you don't want to
cook something in the Cheyenne or power supply. You *could* use a variac on
the AC supply except that'd probably reduce the filament voltage and maybe
the bias voltage too much. Then again, perhaps you could find a happy
compromise, such as reducing the AC input voltage to where the filament
voltage dropped from a nominal 6.3 to only 5.5 or so (or 12.6 to 11.0),
which is a drop of about 13% which would drop the HV from a nominal 820 to
715, not too bad (of course, the LV will drop the same). No variac? Try a
filament transformer wired as a "bucking" transformer; I do that for my
shop lights now and that's caused my lights to last a lot longer than the
usual 3 months or so than on the full AC line voltage.

But when you get done, you'll have a mod that would be worthy of being
added to KB9JJA's web pages of Heath mods (see
http://members.accessus.net/~dwentz/kb9jja/heathkit/ )

73, Steve K0XP

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