[Heathkit] SB-220 meter question

[Robert Dorchuck]

Jack,
Isent this to the list last week but I never saw it posted so here it is 
again.  I'm not sure about the HM-2102 meter.


 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 8/16/2016 9:37 PM, jack m wrote:
> Just wondering - the meters in the HM-102 and HM-2102 RF output/SWR meters are physically the same size as the SB-200 and SB-220.  What are the electrical characteristics of the HM meter movements?
>   
> If they are the same as the SB linear movements, it certainly is easy to change the faces of these to replace a broken or damaged SB 200/220 meter - and definitely lots cheaper based upon the prices I see for complete used HM's versus just the used meters for the SB linears!
>   
> If I recall, correctly, from  an earlier thread on one of the reflectors, all the small SB equipment meters differ only by the face, and all meter movements read full scale with 1 ma current.  I have changed faces on several of these with great success.
>   
> Jack  W3RU
>   		 	   		
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