Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => AmpTools/Tech Tips => Topic started by: jjasilli on January 20, 2011, 08:36:36 pm
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In a period of endless regression, I seem to be rebuilding test equipment instead of amps!
The 2 meter movements on my Heathit PS- Regluated Power Supply Model PS-4 contain grit, like rotted pieces of bakelite; and the mA meter tends to stick on the way up @ the halway point of 75mA. A light tap gets it moving again. The meter movements seem to be sealed in their clear plastic housings. Is there a way to get in there, or am I better off leaving well enough alone?
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> am I better off leaving well enough alone?
Very likely. If you can't get the box open, you probably shouldn't be fussing with the very delicate stuff inside.
But.....
Take off the wires. Take off the 4 nuts behind. Get the meter out on a clear well-lit bench with a towel or sunday newspaper.
The front probably snaps off. On a different style, screws in the back are covered with wax. It is possible, though unlikely, the cover has been glued.
Two screws allow you to slide the scale-plate out from under the needle.
After that.... go very-very carefully. Even a 1mA movement is more delicate than some (mechanical) watches.
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Good Call! The rear of the plastic housing had four little inlets - must have been sealed with very brittle, dried out wax; not glue. Anyway I popped-off the cover cover and got all the crud out of the meter housing. Now, should I lubricate the meter works or leave it alone?
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The movement is NOT!! lubricated.
If clean, it works great.
If gritty, you have real trouble. It is not made to be taken apart. The springs and coil are VERY easy to bung beyond all hope.
It would not be a sin to get two $2.99 DVMs.
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Thanks for all this info! Now I can finish the restoraton job as well as possible. :smiley:
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Done & calibrated ! Cleaned inside and out. The ancient filter caps and "signal" caps were replaced too. With my soldering iron set to minimum heat, I melted the old wax holding the meter housing together; cleaned out the debris; re-assembled the 2 meter housings; and resealed them with soft wax.
I don't have a load handy, so I'll have to wait to see if the mA meter still sticks.
I'd be lost without your continued help. Thanks again!