[Heathkit] Screen dropping resistors (was DX-100B on Phone - bad audio distortion /oscillation)

[Rick Poole]

I wish Heathkit had put reference designators (R6, C14, etc.) on 
their schematics.  Sure would have made it easier to explain things. :-(

In the DX-100B, the PA screens get their voltage from the 800-VDC PA 
plate supply, through two 10K ohm 10 watt resistors in 
series.  (Nothing connects to the junction of the two 10K resistors 
so why they couldn't have used a single 20K... but, I digress...)

The HV measures 840 volts on my Simpson 260 (a little higher than 
shown on the schematic) and the PA screen voltage is 187 volts, 
almost exactly what is shown on the schematic.

The power dissipation for that voltage drop calculates out to be 21.3 
watts, or 10.65 watts per 10-watt resistor.

Just a tad too much.

Some previous owner had added a third 10K ohm 10 watt resistor in the 
series, dropping the screen voltage to around 145 and the power 
dissipation through each resistor to a more comfortable 5.5 watts.

Is that a known modification for the DX-100 or is it something some 
previous owner dreamed up after he burned his fingers on the red-hot 
screen dropping resistors?

Will dropping the screen voltage from 187 down to 147 cause any problems?

Seems like I should get a couple of 10K ohm 20 watt resistors and use 
those.  I could get a 20K ohm 30-40 watt resistor but the way it's 
physically mounted, the two connection points are too close 
together... there is a spare terminal located in a strategic location 
so two 10K resistors in series will be easier to mount.

Rick WA1RKT