Understanding my tuning meter

[Binkman]

incandescent.. green sleeve fooled me. though I can't find the SM for this model I looked up the 8910 thru 9910 models and all list 2 pilot lamps rated at 8v 0.25A and 8v 0.05A.
Hope it helps.

 

[audiodummy]

The incandescent bulb in my STA-64B burned out, the bulb is so small and unless you had a fairy violent filament burning, it's very likely you can't see the break without a very strong magnifying glass.

The tiny "wheat" bulbs will be on the order of 20 ohms cold most likely and sure can check with an analog multimeter under Rx1 or Rx10, though best out of circuit. If you must test in circuit, try both ways and ensure both ways (swap probes) conduct fairly well before concluding a good bulb.

You know, I was thinking these old analog multimeters tend to pass a lot of current in Rx1, and may actually light up a tiny low voltage (1.5V) lamp -- maybe more, depending on design. Concern is that if these multimeters can blow semiconductors, it may do stuff with lamps too.

 

[Mantolaman]

Thanks to all! I've taken another look at the termination of these bulbs, and I see that there are several lights originating from there. The off/on light, the dial pointer light, the dial scale light, (not lit), and the meter light, (not lit).
So. resistance check on the Simpson just shows continuity. non conclusive info.
I'll order the new lamps and proceed to install when I get them.

 

[Ylli]

You certainly can, (power the receiver off first) then follow the green wires and measure between them with your meter set to 'Ohms' range. I am not sure what a bulb of that wattage should measure in ohms - let us know what you get and we can then judge if it seems like the bulb filament is intact or not.

Probably have to lift one of the wires, otherwise you will be measuring the secondary of the transformer powering the lamp.

 

[audiodummy]

Actually you wouldn't be measuring the resistance of the transformer in parallel. The bulb will be in series with a transistor that turns the stereo indicator on and off. However that transistor (or IC and its protection/intrinsic/parasitic diodes) may be forward biased depending on your meter probe positioning which should be remedied by swapping the probes.

If you get more than 10K ohms across an incandescent lamp in some orientation of the probes, it probably is burned out or your meter probes are not making good contact.

 

[Ylli]

Actually you wouldn't be measuring the resistance of the transformer in parallel. The bulb will be in series with a transistor that turns the stereo indicator on and off.

I believe at this point he is trying to check the dial light.

 

[Mantolaman]

Update. Installed new lamps and problem solved. Gotta say this was a real test for this old guy to solder those tiny wires! Couldn't believe one tiny lamp at the end of the dial scale would illuminate clear down the length of it.
And a big thank you to all you guys for helping me sort it out.