Electronics > Repair

B&K 650 tube tester - need replacement meter


Does anyone know the specs for the meter used in the B&k 650 tube tester? I am looking to replace it with a similar meter and I can't find out the resistance of the coil or the full scale current.  I can't find any markings on the meter.
The meter was damaged when I purchased it as-is.  Upon testing the meter with a 10K ohm resistor in series with a power supply, the pointer started to move with about 10v and did not reach full scale with the limit of my power supply at 33v.  This voltage seemed too high for this meter.

Is this in-circuit with the antique capacitor C4 200uF 6V across the meter? I'd expect that cap to be defective, along with every other electrolytic given their age.

It would be strange to have such a high full-scale current, you seem to be around 3mA. The 6AT6 is rated 1mA max. plate current, so the meter movement seems off.
There are some mods to limit pegging the panel meter hard, hopefully it is not damaged. Try a much smaller series resistor say 1k with your power supply and closely watch the meter movement, for sticking, or linearity if 1/2 scale is 1/2 the full-scale current if you can get there. You can measure the panel meter ohms as well.
I have seen contamination inside (metal chips) cause problems as well. Had to do surgery and use masking tape to pick up everything stuck to the magnet inside, of panel meters.
Check closely the meter faceplate for any text about the meter movement. It might match other B&K tube testers but just have a different faceplate.

Thank you for your reply.
I can not find any markings on the meter face indicating the meter movement specs. (see photo).
The meter was damaged when I received it.  The pointer would not move.  I got the pointer to move freely but it would not measure any current.  After checking the solder connections on the spring, the meter would move with current applied although it took too much current to move it half-way.  I will try your suggestion with a 1k resistor.  Usually these meters are 100ua or a little more.

Different model from B&K but the meter has a cap across it and a rating of 1mA with a resistance of 100 ohm.

Might give you something to start from.

Model 650 manual with calibration and schematics. Unfortunately there are no details on the meter itself.

At a minimum make sure the cap is not shorted.....


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