Precision Apparatus EV-10A – Multi tester & VTVM – Restore / Repair

This is another strange looking instrument from 1950s era.  Took me a while to understand what  it is really, so here is the summary –

It is a VTVM + Normal Volt Meter. Which means it can operate without power as well with trade off of low input resistance.

  1. Center Zero VTVM  – Yeah, Zero in the center of the dial, you can read + and -ve without changing the probe polarity or Switch
  2. DC VTVM  – Max volts – up to 6000Volts
  3. Traditional Analog Multi Meter  (AC/DC/mA & dB) – No need for Power for normal measurements. For this left side of the dial is zero, like traditional meters
  4. HV Volt Meter – up to 6000 Volts, both on normal meter and VTVM.
  5. HF AC Volt Meter
  6. Gig Ohm Meter  – up to 2GΩ.
  7. Input resistance 13.3MΩ till 600V, 26.6 M till 1200V and 133 MΩ@ 6000v Input in VTVM mode, 1kΩ/Volt in normal volt meter mode.
  8. Can do up to 60KV with Additional HV Probe !
  9. Up to 12A Ammeter
  10. 70dB for output (AC/Sound/xmitter output) measurement

Here is the page from the 1952 catalog

Screen Shot 2018-11-15 at 10.39.48 PM

Here is a video of the restoration

 

Details of the restoration are logged below.

So here is how I received it –

before

Here  it is now, after restoring, showing

the center zero VTVM in action.

IMG_1339

Here is the map of front panel for the different functions, including VTVM and normal voltmeter  inputs.

IMG_1339

Resistance/Current/dB/Output  measurement jacks.IMG_1339 copy1 copy

The difference between dB and Output jacks is the presence of blocking capacitor C1 in output measurement Jack. dB measurement assumes direct sound AC input – eg from the speaker terminals –  where as “output” measurement jack can be connected directly to the plate of the output tube, and there is a built in .01µF/600V capacitor in the meter to block the DC B+ on the plate.

Screen Shot 2018-11-15 at 10.30.08 PM

Restoration

Very simple process, unless the tubes are bad.  Just two capacitors to replace. one is the C1 in the above picture – the DC blocking cap.

IMG_1330

And the replacementIMG_1336

2nd is the main power supply filter cap,

IMG_1328

And the replacement,IMG_1337

I removed the meter movement to clean it, also showing the old caps

IMG_1335

Few pictures of internals – Note: Meter movement is removed for cleaning.

IMG_1325

Close look at the tubes, 6C4 Triode, OA2 regulator and 6X4 rectifier.

IMG_1326

Dial  is substantially large, comparing it with a complete multi meter

IMG_1334

Here is the front panel removed, you can see the 1.5v X 2 cells inside the cabinet, used for resistance measurement.

IMG_1338

And here is the unit after cleaning and reassembly.

IMG_1345

Here are few measurements

Normal multi meter mode  – Voltage (DC) Measurement.Note: Power  is off -. Input terminals are the pin tip jack – labeled DC-AC-V-mA-dBdcv

DC mA – Note the series resistor.

dcma

Now to VTVM Mode, Power on and use VTVM Probe.

VTVM in positive polarity ie. Probe +ve goes to battery +ve and -ve to battery -ve

vtvmpos

VTVM in negative  polarity ie. Probe +ve goes to battery -ve and -ve to battery +ve

vtvm-neg

As center is zero

And quick resistance check in 2GΩ range.

res

Thats it.  I did not calibrate it as  the readings were “kinda of ” close and I did not want to poke around. May be some time later.

Disclaimer
I have no commercial affiliation with any of the products/organizations/individuals mentioned in this blog.
The information provided here is for educational purpose only.
You are free to distribute this as long as it stays original with all information as is here and it is free and you don’t scavenge any tubes from any scopes or this blog.

NO electrons were harmed during the repair/filming  of this instrument restoration. All free electrons found inside the unit were  rehabilitated to the nearest vacuum tube.

NO EXTRA SCREWS OR PARTS WERE OFFICIALLY FOUND AFTER REASSEMBLY. UNOFFICIAL EXTRA ITEMS WERE DISPOSED OFF SECRETLY AND DECLARED AS “EXCESSIVE ASSEMBLY” DURING MANUFACTURE.

Please do report any errors or stupidity.

=== THE END ===

Back to Home Page for more restoration projects

 

2 thoughts on “Precision Apparatus EV-10A – Multi tester & VTVM – Restore / Repair

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