SB-200 Power Supply

[Ray Friess]

I noticed the same thing on my sb 200 and got the same advice about the voltage
divider resistors.  I have not yet changed them out, figuring that because I
use an external wattmeter, I can still tell if the amp is working up to specs
or not.  However, I may get around to changing them sometime...
Ray  wa7it


Quoting Stu Lyon <w6cux at EARTHLINK.NET>:

> 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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