[Heath] SB-200 problems...again...

[Kenneth G. Gordon]

On 19 Sep 2011 at 7:45, Glen Zook wrote:

> Not to ask a stupid question, but have you checked the value of the
> meter shunt resistor? It is a 1.5 ohm resistor, R-15 on the 
schematic

Hello, Glenn. Yes. R-15 is the grid meter shunt. In fact, I checked 
every resistor in the grid- bias string and all were within spec. 
However, just to be on the safe side, I replaced R-15 with a new, 
checked, metal film 3 watt 1% resistor. Results unchanged.

>. Also check C-19 which 
> is a 2 mfd @ 150 volt electrolytic.

I did check that, and although it checked out OK, I plan to replace 
it with a modern metal film cap as soon as they arrive from Mouser.

I have not yet checked the PLATE metering resistor R-12 (1 ohm 5 watt 
1%) but will asap.

I am wondering (but don't see how) if my replacement of the power 
supply capacitor- equalizing/bleeder resistors with 100 K resistors 
(rather than the original 30K) would effect the plate current 
reading. I would not think so since they, and the meter shunt 
resistor, are all in series, but I am still suspicious.

I also replaced the power supply filter caps with modern units at the 
same time I did the resistors.

I am going to (carefully) lift the ground end of R-12, and connect a
miliammeter in there to see what my actual plate idle current reads, 
and will compare readings.

Lastly, when I discovered the apparently high-resistance in the 
Harbach soft-switch, I contacted Harbach, but he was confused by 
that. He didn't see how that could occur, and I don't either...

Ken W7EKB