[Heath] Concerning the HP-23 series of power supplies.

[Kenneth G. Gordon]

A couple of things I might mention concerning the HP-23 series of power 
supplies:

1) IMHO, the best of the series is the HP-23A, for several reasons. Basically, 
it is the most versatile of the bunch, having both 6.3 VAC and 12.6 VAC 
filament sources, both variable and fixed bias sources, a switch to change 
the low B+ from the 250V to 300 V setting without having to open it up and 
make wiring changes. The first model had no low-B switch, nor a pilot light, 
and models after the "A" model were much simplified in other ways.

2) Secondly, the "A" model is the first of the series which had closer to the  
correct high-B+ of the specified "820 VDC". 

If you look carefully at the schematics of the early HP-23 and that of the 
HP-23A (and subsequent models) you will see that the secondary voltage of 
the power transformer is 268 VAC in the HP-23, but 282 VAC in the later 
models.

Since the HP-23 series uses a voltage doubler for the high-B+, this results in 
a DC output voltage of about 758 VDC, whereas the HP-23A and later 
models' 282 VAC results in a DC output voltage of 798 VDC, or at least 40 
VDC higher.

Somewhat surprisingly, this makes a big difference in whether or not the rigs 
achieve their rated output power.

Despite this, the specified high-B+ output voltage is listed as "820 VDC" in all 
cases. There is simply no way that the early model can achieve this, but the 
subsequent models often can, depending on the line-voltage, and the 
condition of the filter capacitors.

I have both an HP-23, to which I have added a low-B switch and a pilot light, 
and an HP-23A, both of which I have refurbished. They are both very good 
supplies, but I use the "A" model for use with my transceivers.

YMMV.

Ken W7EKB