Heathkit SB 220 Amplifier

[Gene A. Nailon]

FROM: Gene Nailon  K5DLE  k5dle at juno.com
17 Oct. 2004

Hello Bert;

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.

Best regards,

Gene
---------------------------------------------------------
Date:    Sat, 16 Oct 2004
From:    Bert Larson <W0YYG at CENTURYTEL.NET>
Subject: Heathkit SB 220 Amplifier

Gentlemen:

I am in " NEED " of the Plate Current Meter for the SB 220
Amplifier.  ( 0 - 1 ampere )

If an Exact replacement is not available, I could use a 0 - 1
Ampere Meter, to be used as a Reference, when determining the
Ohmic Resistance of the SHUNT for the 30ua meter which will bring
the 30ua meter at Full Scale, to 1 ampere.

Can you be of some Help ?

W0YYG at centurytel.net
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