Posts Tagged ‘VACUUM TUBE MULTIMETER

22
Jul
22

ON THE BENCH: Vintage Simpson Model 303 Analog Vacuum Tube Volt Meter – UNTESTED

Order Summary From shopgoodwill.com

Subtotal$14.99

Tax$1.90

Shipping $8.78

Handling$3.49

Additional Donation$0.84

Order Total$30.00

Ask around for a recommendation for a good multi meter and get plenty of suggestions. Most people like the digital auto readout that takes the guesswork out of changing knobs and settings to measure voltage and resistance. The name Simpson is synonymous with a high quality meter. Many techs from the day had one on the bench or in the field. namely the model 260 in a few variants. Just a rough check now, a current 260 new will be around $400.00 USD. they are know for reliability, ruggedness and accuracy. Because of the quality build, many, many of the 260 series can be purchased on the secondary market. That is if an analog meter is your game.

While digital meters can be inviting and easy to read they don’t show any transients quite like an analog meter. True, some digital meters have a bar graph display that will show changes, it’s not as telling as the sweep of the needle of the full analog meter. It’s better than digital when peaking measurements for calibration. Using the meter often the scales of the meter get familiar and are read with ease.

Presently I have a multi meter, another purchased used and refurbished the small Amprobe AM 2A meter also purchased from shopgoodwill.com for $18.03 delivered. It does the job after frying out a china sourced basic not more than a few dollars analog meter.

Without a long winded explanation of the benefits of a high impedance input meter for accuracy, another tech staple is the VTVM or irreverently know as the vommit meter. As the acronym implies, Vacuum Tube Volt Meter, has a vacuum tube on the input for accuracy. Mostly for bench use because of the need for 120 vac power, they are a must have if precision voltage measurement is required, especially for calibration of equipment to manufactures standards. Some calibration instructions will list a VTVM as a requirement and may even specify the brand.

The Simpson Model 303 Analog Vacuum Tube Volt Meter is a good example of a good all around fairly priced used multi meter, rugged and well built as we will see. Made to last these are excellent candidates for over haul.

First a couple of tips if you are following and will attempt repairs:

BAG AND TAG FASTENERS AND PARTS WHEN REMOVED AND THEIR LOCATION.

TAG CIRCUIT BOARDS AS TO THEIR PLACEMENT WHEN REMOVED

TAG WIRES AS TO THEIR CONNECTION POINT AND FUNCTION WHEN UNPLUGGED/DE-SOLDERED

TAKE PHOTOS BEFORE DIS ASSEMBLY, AND/OR KEEP NOTES OR A LOG OF PROCEDURES AND STEPS

PREPARE FOR THE POSSIBILITY THE REPAIR MAY SPAN SEVERAL WEEKS AS PARTS ON ORDER OR OTHER JOBS ARISE.

DOWNLOAD/PURCHASE USER MANUAL. SCHEMATICS AND PARTS DIAGRAMS (ACTUALLY THIS CAN BE DONE PRIOR TO PURCHASE TO SEE WHATS INVOLVED)

NOTES ANY DIFFERENCES ON SCHEMATICS AND DIAGRAMS, MANUFACTURES CAN BE NOTORIOUS FOR NOT SUPPLYING AN “AS BUILT” OR ERRATA OR REVISION SHEETS. SOME SCHEMATICS MAY BE FOR A GENERIC MODEL.

HAVE THE PROPER TOOLS AND TEST EQUIPMENT AVAILABLE

CONSULT REPAIR VIDEOS AND FORUMS FOR INSIGHT AS TO WHATS INVOLVED AND COSTLY PARTS AND ITEMS THAT MAY OR MAY NOT BE AVAILABLE

LETS GO

THE ARRIVAL
FIRST LOOK THE ACV INPUT HAS BEEN REPLACED WITH A PUSHBUTTON SWITCH
THE PREVIOUS OWNER WAS OBSESSED WITH THE SERIAL NUMBER, ETCHED IN SEVERAL PLACES ON THE METER

THE COAXIAL CONNECTORS OF THESE METERS ARE OF A PROPRIETARY SIZE, NOT READILY AVAILABLE, THERE ARE SEVERAL WORKAROUNDS RESEARCHED THROUGH THE INTERNET. EBAY OFFERS A CUSTOM REPLACEMENT SET IF YOU DON’T WANT TO MODIFY THE METER, AT A COST

WIRE WOUND PRECISION RESISTORS BANKS , ADJUSTMENT POTS, SELECTOR SWITCHES AND TRANSFORMERS
THE PUSH BUTTON IN THE PLACE OF THE ACV INPUT ??? TRACED THE SCHEMATIC, APPARENT IT IS A GROUNDING SWITCH PROBABLY FOR ZEROING THE METER DURING RESISTANCE MEASURMENTS
THE ROTARY SWITCHES ARE IN GOOD SHAPE AND WILL BE CLEANED WITH DEOXIT
BATTERY CLIP IN GOOD SHAPE NO EVIDENCE OF BATTERY LEAKAGE
ONE OF THE 2 TUBES , TO THE LEFT THE SELENIUM RECTIFIER THAT WILL BE REPLACED WITH A DIODE

REMOVAL OF THE FACEPLATE AND GLASS
METER ASSEMBLY IS EXCELLENT
REMOVAL OF METER MOVEMENT FROM THE CASE
THE TWO TUBES, HAVE NO WAY OF CHECKING THEM AT THIS TIME

POTENTIOMETER ADJUSTMENT BLOCK
BATTERY CLIP AND METER CONNECTIONS REMOVAL
REMOVAL OF THE STANDOFF FOR THE RESISTOR GANG
THE OTHER SIDE IS A STEPPED STANDOFF FOR THE RESISTOR GANG
SET UP AS SHOWN
DCV INPUT JACK, NOT ORIGINAL WIRINGING
HOLDING THE INNARDS, ROTATE AROUND THREADED THE GROUND PIN JACK IN THE FRONT TO REMOVE GUTS FROM THE CASE. OR UNSOLD ER ALL THE GROUND LUG WIRES (NO)

THANKS TO THE WIRING CABLES AND WRAPPING, THE GUTS STAY TOGETHER , SO MUCH FOR CONNECTORS AND FRAGILE RIBBON CABLES, ALL POINT TO POINT WIRING
THER ARE ONLY 4 CAPACITORS IN THE METER ALL TO BE REPLACED

CLEANING STORAGE AND BAGGED AND TAGGED ITEMS
THE BAKELITE CASE PARTS CLEANED
SOME OF THE PAINT WAS REMOVED DURING THE SOAKING PROCESS AS EXPECTED WITH VINTAGE ITEM
THE LETTERING WAS RESTORED WITH A PAINT PEN, SOMEONE DRILLED HOLES IN THE BACK TO ACCESS THE ADJUSTMENT POTS
TEST FIT OF THE CASE AND KNOBS
BECAUSE OF THE HEAT FROM THE TUBES, VENT TUBES ARE ON BOTH SIDES. NO HANDLE WAS INCLUDED
MAYBE OVERKILL, I BUFFED UP THE BAKELITE ON THE BUFFING WHEEL

METER MOVEMENT FINE, ZEROS PROPERLY
REPLACEMENT CAPACITORS FROM DIGIKEY
CHECKING ASSEMBLY
LEAVING THE RECTIFIER IN PLACE FOR PROPER SUPPORT, THE DIODE AND RESISTOR AFTER THE TRANSFORMER WAS HEAT SHRINKED INSULATED AND TUCKED AWAY
ONE THE THE CAPS REPLACED, NEW COMPONENTS ARE SMALLER THAN ORIGINALS
BATTERY IN PLACE
NOT SHOWN, WITH A DREMEL FITTED WITH A REAMER, I CAREFULLY MARKED OUT THE INCREASED DIAMETER NEED TO ACCOMMODATE THE 259 COAX CONNECTOR JACKS. MOST INFO ON THIS MOD SUGGEST THAT DRILLING HOLES WILL CRACK THE BAKELITE. THE CONNECTORS JUST FIT ! ALSO WITH THE SANDING DRUM MACHINED THE SURROUNDING THICKNESS TO ACCEPT THE DEPTH OF THE ATTACHMENT NUT.\ THREADS THE ATTACHING NUT WAS SLIGHTLY GROUND ROUND TO FIT THE CASE
THE CAPS REPLACED
CONNECTORS AND JACKS VIA ALI EXPRESS
SOMETIMES MYSTIFIED WITH THE MYRIAD OF REPLACEMENT CAPACITORS, HOPE THEY WORK
THE FINISHED METER LESS THE LEADS AND PROBES. AT FINAL ASSEMBLY IT WAS TESTED BY JUMPER WIRES, THE TUBE HEATER FILAMENTS GLOWED AND THE METER WAS ABLE TO BE CALIBRATED AS PER INSTRUCTIONS YEA! YES, WITH THE MALE CONNECTORS SCREWED ON THERE IS ENOUGH CLEARANCE FOR THE SELECTOR KNOBS TO BE ROTATED.
THE REAR, THE LINE CORD HAD BEEN SPLICED, NO PROBLEM FOR ME
LOOKING INTO THE PROCESS OF BUILDING MY OWN LEADS AND PROBES, HAVEN’T DECIDED YET AS THERE ARE AVAILABLE KITS ON EBAY SO I WON’T HAVE TO ORDER ALL THE PARTS I DON’T HAVE



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