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Author Topic: SB-102 meter damping  (Read 339 times)
W5RKL
Member

Posts: 1078




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« Reply #15 on: December 08, 2018, 02:55:31 PM »


Some have stated adding a capacitor across the meter will help reduce meter bounce. Others
have stated changing R104, V3's 22K 1 watt screen resistor, to 22K 2 watt. Adding a capacitor
across the meter terminals or changing R104 from a 1 watt to a 2 watt resistor will have no affect
in meter bounce.

Meter bounce is primarily a mechanical issue. Naturally a circuit the meter is connected to where the
voltage decays rapidly or slowly to zero will have an affect on meter bounce. In this case the SB-102
RF output, GRID, HV, and PLATE meter circuits will have a rather rapid voltage decay to zero than the
slow decaying voltage in the receiver AGC and transmitter ALC voltage circuits.

I performed a simple rapid decaying voltage test  using a couple of Heathkit HW-100/101 and SB-400/401
meters. Both meters have the exact same electrical specifications, 1ma at 100 ohms, as the SB-100/101/102
meters have. I used a 6.15VDC lantern battery and a series meter multiplying resistor of 6.5K. The tests
were perform with and without a 0.0047ufd disc capacitor connected across the meters. The meter
multiplying resistor was calculated using Ohms Law formula

R = E / I

where

"E" is 6.15VDC
"I" is 1ma

6.15 / 0.001 = 6,150

I didn't have a 6,150 ohm resistor so I used the next "highest" value resistor, 6.8K. Don't use the next "lower"
value as that will result in a higher current flowing through the meter which could damage the meter coil.

Click the link below to watch the meter tests I performed showing meter bounce with a rapid decay of voltage
from the meter circuit.

http://w5rkl.com/wp-content/uploads/2018/12/HW101-Meter-Bounce-Test.wmv

73
Mike W5RKL
www.w5rkl.com
RMC(SW) USN RET
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KC1BMD
Member

Posts: 886




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« Reply #16 on: December 08, 2018, 03:23:49 PM »

Mike, thanks for sharing that video. Although I cannot hear the meter, I suspect that when you are close enough with no noise around you would also hear the meter hit the stop, especially on the down swing. In any case, the bounce looks quite similar to mine, so I will assume it's the nature of the meter mechanicals and I won't bother chasing it further.
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W5RKL
Member

Posts: 1078




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« Reply #17 on: December 08, 2018, 07:15:38 PM »

In the video link I show that Ohms Law calculation stated I would need a 6,150 ohm resistor for 1ma FS. I said I
didn't have a 6,150 ohms resistor but rather I would use the next higher value resistor I had which
I said was 6,500 ohms The actual next higher value resistor I had was 6,800 not 6,500.

Sorry for the misspoke resistor value in the video.

73
Mike W5RKL
www.w5rkl.com
RMC(SW) USN RET


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KC1BMD
Member

Posts: 886




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« Reply #18 on: December 09, 2018, 08:28:23 AM »

I guess that would explain why it did not get closer to FS. Glad you fessed up Mike! Smiley. Did you also hear the "ping" of the needle hitting the lower stop on the down swing? I just don't recall hearing it in the past but it likely did.
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