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THE AM BULLETIN BOARD => Technical Forum => Topic started by: Opcom on July 21, 2020, 01:14:11 PM



Title: 800Hz panel meter question
Post by: Opcom on July 21, 2020, 01:14:11 PM
I have a nice pair of panel meters, 0-150VAC 800Hz. They do indicate correctly on 60Hz, but there is too much current or something. The needle almost 'sticks;' when energized but is free when un-energized, that is, tilting the meter right-left-right it swings normally. It's not ruined, but I'm trying to figure out how to use it even if I have to modify something like the rectifier or multiplier etc. As far as I can tell it's a moving coil movement, not a vane. I have assumed it's aDC movement, but have not opened them.I thought I knew alot about panel meters, but apparently not. I would like to use them to show both sides of the 240V line voltage.


Title: Re: 800Hz panel meter question
Post by: KA3EKH on July 22, 2020, 11:06:00 AM
Maybe meters from a TBW or GP series WW2 transmitter. They used 800 Hz power supplies because they required smaller transformers and filters in the power supplies and they also used the raw 800 Hz to feed the suppressor of the 803 PA tube to develop A2 or AM CW.
The TBW had a gasoline powered 800 Hz generator and cannot imagine what that sounded like in operation. I had a TBW that I built up a regular AC power supply that I use to run and somehow think it had a meter that had two scales one for input voltage and a second scale for 0 to 15 volts that was used for setting the filament voltage of the PA tube, may a want to check because your 150 volt meter may just be a 15 volt meter?



Title: Re: 800Hz panel meter question
Post by: Opcom on August 08, 2020, 02:03:37 PM
Maybe the mechanism is similar. These have just the one scale and are what looks like a standard GE AC Volts panel meter from the 50's tp 70's, mostly square/rectangular but with rounded corners. The size is perhaps 4" across. The usual very small markings on the bottom of the scale may have a part number, but I recall seeing 800~ there. They are a similar style to the image attached.

I noticed there is a very slight vibration of the pointer on 60Hz. I've see 400Hz ac meters indicate well on 60Hz but more current was drawn.

Since it's an AC meter with a moving coil, it could either be the permanent magnet stator type using a rectifier,  or the electromagnetic stator type which does not need a rectifier if those are/were still in use. Maybe I could take note of the meter's resistance and try a little DC current.

I can't tell more without taking it apart and I'd rather not for fear of breaking it.
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