[Boatanchors]Heath HP-20 versus HP-23

[Richard Post]

Hi Phil and others on this thread,

I've had it confirmed that the 600 volts from the HP-20 is under 
load.  Other than its lower resistance bleeder, the HP-20 should 
theoretically have a no-load voltage that comes close to the HP-23. 
I also came to the same conslusion that you did on the higher 
internal resistance of the lighter power transformer of the HP-20. 
The HP-23B manual notes 700 volts with a load of 250 MA.  Its 
continuous rating is 150 MA which I suppose would be at about 750 
volts or so.

The HP-23 series were used with the Heathkit monobanders which use a 
pair of 6GE5 sweep tubes that have a design-center max plate rating 
of 770 Volts.

The Swan 175 monobander uses the 6DQ5 which has a design-center max 
of 990 plate volts (RCA and Tung Sol specs) or 900 volts (Sylvania 
specs).

The tube should be able to handle it as well as any of those used by 
Heath, but I will try to drop the voltage somewhat and watch the 
current and my tune-up times.

Has anyone tried to drop the volts on these a bit by series zeners or 
a zener and high voltage transistor combo?  A failure mode of short 
circuit would just be back to regular voltage or open, no high 
voltage.  This would actually cut back the no load voltage as opposed 
to use of a resistor.

73,
Rich

http://www.qsl.net/kb8tad


At 3:48 PM +0000 6/23/04, Philip B Atchley wrote:
>Rich et al,
>This is pure conjecture (based on sound scientific reasoning) as I don't
>presently have a HP23 and HP-20 here to compare.
>
>HP-23:  Current wise the HP-23 is a much heavier duty power supply, being
>designed to handle two 6146 (or similar) Finals while the HP-20 is
>designed for rigs with one final.  Heath states the HP-23 will output 800
>Volts without a load, dropping to 700 Under load (two finals).  Hence, I
>interpolated that it'd probably put out something like 750 Volts with one
>Final running on it (the Elmac).  It seems that the "later" rigs also
>pushed their finals a little harder Voltage wise (up from the typical
>500-600 Volts of the earlier rigs to 700 Volts or so).  This perhaps to
>either get more power output or because the newer rigs were mostly SSB
>with NO AM plate modulation like the Elmac and other rigs of the earlier
>times had.  I suspect the modulators of the earlier rigs might "break
>down" under 700 Volts or more. 
>
>HP-20:  This is a lighter power supply intended to run the older rigs
>running a single 6146 or similar final, often with a Plate Modulator.  In
>this supply Heath doesn't seem to say, but I suspect that under "key up"
>the Voltage may rise to well over 600.  However, since the supply is
>designed for less current (single final), it's transformer is most
>certainly wound with a lighter gauge wire, both in the secondary and the
>primary windings.  This would lead to higher resistance, causing a
>greater Voltage drop under load, bringing it down to the stated 600 Volts
>or so.  
>
>Does all this make sense to you?
>
>
>73 de Phil KO6BB
>  > Thinking of using the HP-23 for the Swan.
>>
>>  73,
>>  Rich
>>
>>  Boatanchor Pix
>>
>  > <http://www.qsl.net/kb8tad>
>  >
>>
>  >
>>