restoring RCA Voltohmyst Senior need part source

[Jeff L]

I'm restoring a RCA Voltohmyst and came across a 4 section potentiometer , 10K, 1/4 Watt, p/number 221336. Somebody overamped one section,and now the plastic adjuster won't move. Any possible source?

[alm]

Given that not everyone may be familiair with this particular instrument, maybe posting clear pictures of the part might help find a replacement if it's not a custom part.

[Synthtech]

I’ve been restoring a Voltohmyst along with several other VTVM’s and tube testers and a couple of vintage but solid state multimeters. My advice with any equipment repair or restoration of devices with a moving coil meter that is decades old is to first, before anything else to test the meter movement itself to see if it can still reach full-scale-deflection at the stated FSD current.

It’s not that uncommon for some old meter movements to lose field strength in their permanent magnet and in some test gear this makes it unable to be calibrated as the meter just can’t deflect enough. Be very careful though never to try and test a meter movement with a multimeter ohms range, many movements have FSD current in the uA range so you need a power supply and a decade resistance box and a precision resistor to measure current drop and a good multimeter to measure that drop and to calculate the meter coil resistance. Putting a multimeter on ohms range directly across the meter will damage it as the multimeter test voltage is too high.

[Stray Electron]

I’ve been restoring a Voltohmyst along with several other VTVM’s and tube testers and a couple of vintage but solid state multimeters. My advice with any equipment repair or restoration of devices with a moving coil meter that is decades old is to first, before anything else to test the meter movement itself to see if it can still reach full-scale-deflection at the stated FSD current.

It’s not that uncommon for some old meter movements to lose field strength in their permanent magnet and in some test gear this makes it unable to be calibrated as the meter just can’t deflect enough. Be very careful though never to try and test a meter movement with a multimeter ohms range, many movements have FSD current in the uA range so you need a power supply and a decade resistance box and a precision resistor to measure current drop and a good multimeter to measure that drop and to calculate the meter coil resistance. Putting a multimeter on ohms range directly across the meter will damage it as the multimeter test voltage is too high.

  X2.  And I'll add that the meter movement in many of the High Grade meters is quite delicate and they frequently don't survive being shipped.  Ask me how I know! 

[GLouie]

I have a 1955 original manual for the RCA Senior Voltohmyst here and don't see that part listed. There may have been design changes, so yes, photos, dates, serial number may help.

[Jeff L]

Decided  to go with brand new, sealed 18 turn potentiometers from Digikey-- next day delivered--  CND$3.75 ea.