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

[Wilson Lamb]

The resistor in series with the bleeder is for measuring voltage.  Lowering 
the equalizing resistors will make the B+ read high by the factor of 
reduction of the equalixiing Rs.  I expect the shunt should now be 30% of 
its original value.
WL
----- Original Message ----- 
From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
To: "Glen Zook" <gzook at yahoo.com>
Cc: <Heath at puck.nether.net>
Sent: Monday, September 19, 2011 11:37 AM
Subject: Re: [Heath] SB-200 problems...again...


> 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
>
>
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