[Heathkit] SB-220 meter question

[Robert Dorchuck]

Ron,
 From my SB220 info:

-----------------------------------
The original plate meter is Heath P/N 407-145. which is a Ideal Precesion
meter. 1400ohms, 200ua, .28v. The basic meter movement in both meters is the
same. 1400ohms, 200ua, .28v. The multimeter for grid, volts and relative 
power
is Heath P/N 407-146. This is also the same basic meter movement used in the
SB-200 Amp. Its P/N 407-103. Just put your old dial scale on the new meter.

Looking at the circuit for the SB-220, R1 (1 ohm 5W) is your meter 
shunt. With
1 amp of current flowing you will develop 1 volt across this resistor. R2
(3600ohm 5W) drops the voltage of 1 volt to the .28v required for full 
scale on
the meter.

In order to calculate the value of resistance needed for the 30ua meter you
will need to know the resistance of the meter.

I'm sure you could change R2 to make the 30ua meter work.

You could also use the basic meter movement for the HM-102 Watt Meter, P/N
407-155 100ua, 1000ohm, .1v. by changing the value of R2 to 9.0k ohm, the
closest standard value is 9.1K ohm at 1/4W or more.

---------------------------

73
Bob  W6VY

On 8/14/2016 12:51 PM, Ron Bussiere via Heathkit wrote:
> Hi. I was wondering if anyone had the following, about the 2 meters used in the SB-220 amp:
>
> I know the P/Ns:
>
> 407-147 Plate current meter
> 407-146 Multimeter
>
> I would like to know the specs. Nowhere in the manual is there a description of the value.  They sure look the same, except for the face, of course.
> 0-1 ma or ?????
>
> thanks!
>
> ron
> N4UE
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