[AMRadio] Heath SB-630 and SB-200 Parts FS

[Donald Chester]

 "Ken, W8EK" <kenw8ek at gmail.com> wrote:

> Resistors for Electrolytic Filter Capacitors:

> In all of the Heath HF amplifiers, they use
> a low resistance value, high power resistor
> for equalizing resistors across each of the
> filter caps. This is problematic in that they
> dissipate a lot of excessive heat, which causes
> the caps to get hotter than necessary,
> and die a premature death.

> The solution to this is to use a higher
> value resistor. It also should have a tighter
> tolerance, so that it equalizes the voltages
> across the filter caps better.

Perhaps it would be better to re-locate them
farther away from the capacitors, if they are
heating up the capacitors enough to shorten
their life. Any HV power supply needs a bleeder
resistor, for safety reasons as well as to maintain
a minimum load on the supply to reduce voltage
sag with variations in the primary load. 

When several capacitors are wired in series
to make up a HV filter capacitor, the bleeder
resistor should be divided up into equal sections, 
so that each capacitor has an equal portion of
the bleeder resistance across it to equalise voltages, 
since the internal (leakage) resistance of "identical" 
capacitors may vary considerably, and the leakage
resistance of a given capacitor may change over 
time, not necessarily in lock-step with the other 
capacitors.

Since a bleeder resistance is required in any case,
just let it serve also to equalise DC voltage across
the capacitors.  No need to have a main bleeder 
resistor in the supply AND equaliser resistors across 
each capacitor as well.

If the power supply has more than one filter capacitor,
the bleeder  resistances should be distributed evenly
across each individual capacitor in each series string,
so that  the total series/parallel "equalisation" 
resistance makes up the desired bleeder resistance.

Don k4kyv