SB-200 Power Supply

[Stu Lyon]

Jim,

The voltage divider resistors are probably off. The R3 
resistor consists of three 4.7Meg/1W/10% in series. Over 
time these resistors tend to drift high. The resistors are 
also over-stressed in that they are rated for 300Volts and 
have 800Volts applied across each one.

One of the improvements Harbach made to the SB-200 
replacement power supply board was to increase the accuracy 
of the resistor string by using 14 - 1Meg precision 
resistors.   http://www.harbachelectronics.com/

I don't think the 100uf filter capacitors have anything to 
do with the low voltage reading -- especially under resting 
bias conditions.

73, Stu W6CUX

James A. Sutherin wrote:
> The above amplifier is wired for 120volt. When I was bring the power
> supply up using a variac, I noticed when the input voltage was 120 the
> HV on the panel meter only read about 1800volts. The power supply cap's
> had been changed by the previous owner to 100uf / 450 vdc cap's. I
> realize the original cap's were 125uf. 450vdc. Is there anything I
> should check to see why I'm only getting 1800 vdc instead of the 2400
> +/- vdc.? Would having the 100uf cap's instead of the 125uf make that
> much difference? 
> 
> Thanks 
> 
> Jim K8DHC
> 

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