The RCA Battery Voltohmystyst

The RCA Battery Voltohmyst .. RCA WV-65A
THE RCA VOLTOHMYST WV-65A VACUUM TUBE VOLTMETER WAS PROBABLY MANUFACTURED IN THE MID TO LATE FORTIES. THE RCA WV-65A VOLTOHMST IS MENTIONED IN AN ARTICLE FROM THE RCA “HAM TIPS” IN JULY 1949.  THERE ARE VIDEOS REGARDING THE METER ON THE INTERNET.  
THIS IS AN UNUSUAL AND RARE VACUUM TUBE VOLT METER BEING BATTERY OPERATED.  IT IS PERFECT FOR RADIO REPAIR. THE METER MAY HAVE BEEN ORIGINALLY MARKETED TO “HAM” RADIO OPERATORS.  
AS WITH ALL THE VACUUM TUBE METERS BUILT BY RCA THE WV-65A HAS THE USUAL ONE MEGOHM RESISTOR IN THE PROBE. THIS ALLOWS DC MEASURMENTS TO BE MADE ON A RADIO WITHOUT INTERFERING WITH THE RADIO OPERATION.  THE PROBE WILL NOT ALTER THE AUTOMATIC GAIN CONTROL VOLTAGE AND WILL NOT KILL THE OSCILLATOR WHEN MEASURING THE OSCILLATOR NEGATIVE GRID VOLTAGE.  
THE WV-65A LOOKS LIKE THE RCA 195 VOLTOHMYST AND HAS A BRUSHED CHROME FRONT PANEL LIKE MOST OF THE 195’S. IT HAS A DC CURRENT SCALE WHILE THE RCA 195 VOLTOHMYST DOES NOT. THE CURRENT SCALES ON THE WV65-A ARE 10 MA TO 10 AMPS.
THE METER WAS DESIGNED TO USE TWO 45 VOLT SERIES BATTERIES AND FOUR D CELL BATTERIES. THE METER CAN BE CONVERTED TO USE A SERIES STRING OF NINE VOLT BATTERIES BECAUSE THEY ARE ACTUALLY CLOSE TO TEN VOLTS.. THE NINE BATTERIES WILL SNAP TOGETHER AND FIT IN  A SHELF THAT CAN BE ADDED AT THE TOP (INSIDE) THE METER. THE BATTERYS ARE THEN CLAMPED IN PLACE INSIDE THE TOP OF THE METER. THE NINE VOLT BATTERYS PROVIDE ABOUT 86VOLTS AND THE METER DRAWS 1.87 MA FROM THE BATTERIES. THIS GIVES A LONG LIFE FOR THE BATTERIES. NINE VOLT BATTERIES CAN BE FOULD TWO FOR ABOUT A  DOLLAR ON THE INTERNET.  I DO NOT USE ALKALINE BATTERIES BECAUSE THE B+ DRAIN IS SO SMALL. IF DESIRED THE ALKALINE BATTERY COULD BE USED FOR THE TUBE FILAMENTS. THE METER USES TWO 1C5 TUBES. THE METER HAS AN UNUSUAL PILOT LAMP.  THE LAMP IS NEON AND FLASHS ABOUT TWO TIMES PER SECOND WHEN THE METER IS “ON”. THIS IS DONE TO REDUCE BATTERY CURRENT. MEASUREMENTS SHOW THAT IT HAS AN ACCURACY OF 7 TO 10 PERCENT ON A FEW SCALES.  THE ACCURACY ON MOST SCALES IS ABOUT FIVE PERCENT.  GREAT FOR RADIO SERVICE! THE SPECIFICATON FOR THE VOLTOHMYST’S ACCURACY IS GENERALLY VAGUE.  THE SPECIFICATION OF MY 195 VOLTOHMYST IS THAT IT USES ONE PERCENT MATCHED RESISTORS. WHILE THIS MAY BE TRUE IT DOES NOT DEFINE THE ACCURACY OF THE METER.
THE WV-65A METER DOES NOT USE POWER FOR THE AC OR DC CURRENT MEASUREMENTS.  THESE MEASUREMENTS ARE MADE WITH THE METER IN THE “OFF” POSITION.  THERE ARE TWO “OFF” POSITIONS ON THE FUNCTION SWITCH.  
THE FREQUENCY RESPONSE FOR THE AC SCALES IS ABOUT THREE DB DOWN AT FIVE KILOHERTZ, AND THIS IS FINE FOR RADIO ALINGMENT. THE IMPEDANCE FOR THE AC INPUT IS ABOUT 12 THOUSAND OHMS ON THE 10 VOLT SCALE AND ABOUT ONE MEG ON THE 1000 VOLT SCALE.  I CHECKED THE 1000 VOLT SCALE USING 400 VOLTS AND IT WAS RIGHT ON. THERE IS NOT A THREE VOLT AC SCALE.    

 THE RCA VOLTOHMYST’S ARE HIGHLY REGARDED METERS FOR DC MEASUREMENTS BECAUSE OF THE METERS HIGH INPUT (10 MEGOHM) IMPEDANCE. IT IS ALSO REGARDED FOR ITS ABILITY TO MAKE RESISTOR MEASURMENTS UP TO 1000 MEG-OHMS. IT HAS GOOD ACCURACY FOR RADIO REPAIR.  NO WARM UP TIME REQUIRED. 


WHEN TURNED ON IT IS IMMEDIATELY READY TO MAKE MEASUREMENTS.  NO WARM UP TIME! THE NEW “VOLT” TEST PROBE WAS MADE USING FLEXIBLE COAX. THE NEW HANDLE WAS  MADE FROM AN OLD LEATHER BELT.

 Questions or Comments? Please e-mail me at whnj@att.net  Thanks, Bill.

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