Posts Tagged ‘SIMPSON 303

17
Sep
22

On the bench.. VTVM Test probe kit.

This a continuation of the repair and restoration of a Simpson 303 VTVM.

The Blue Mat Group Member Series

The final decision was to purchase this kit. $21.35 seemed pricey but the alternative was to scrounge around for parts and/or order the balance of parts I didn’t have. Considering what i would have to do and I wanted to get this job up and running to have as my main meter, I placed the order (eBay).

After receiving this kit I realized that this was the better choice. The coax cables were just the right size and flexible. The other included test lead wire quality matched to boot. All the parts needed were there , no need to raid the parts bins. Plus I would have some parts left over for the parts bins.

The kit, great packaging, recyclable for parts storage or use as seller packaging.

The meter waiting to be completed, My combo LED fluorescent bulb lamp in the reflection.

un boxing or un bagging

attention to detail even a Velcro loop is included.

A quick view of the eBay listing, the seller had pictures that answered all my assembly questions. The finish for this project had been on the back burner for weeks. Retrieved the parts bin, now where did I put that ? (mushroom container) for the repair to get the male parts of the connectors. Now where’s the schematic?

It was the normal start at the bench , prep the soldering iron ,replacing a piece. Then locating the schematic to the meter to verify the placement of the inline resistor to the correct probe and available for troubleshooting if required.. Assembly is straight forward, first I assembled the grounding lead, no problem soldering. The seller specified by pictures , 3 inches of stripping for the coax cables. The hardest part is the fishing of the inner conductor down through the probe handle and out through an angled bore at the end of the probe handle in the metal tip.

R29 1 megohm resistor in the probe, supplied by the kit.

schematic , most of it is the multiple decks of the multi layer rotary wafer switches

replacing the barrel sleeve on the iron.

cross section of the supplied wire from the kit

Once through, some of the stripped wire is pulled through and the probe trim ring is screwed to the top of the probe tip, locking the wire in place and making the connection.

The second time around for the second probe, was problematic, The center conductor was tinned,. After repeated ( time consuming) failed attempts, I fished a length of thin wire solder up from the tip and tacked the center conductor lead to it. Acting as a fish tape, I simply pulled the solder wire through. The wire followed !. Done with the probe set , nice. It’s a bit frustrating and time consuming fishing wires but the probe handles are permanently attached (as i first tried to unscrew them) so they won’t unscrew and loosen as another set I have does frequently. The completeness of the kit even includes labels for the probes and transparent heat shrink . Well Done !

The 1 meg ohm resistor soldered to the center conductor

the angled bore at the top of the probe tip.

using the solder wire as a wire puller

No problem, a time saver I should have used at the start.

tinned lead

folded back for connection to the male coax connector

I soldered the shield braid to the metal bushing

The completed connection less the outer part of the connector

The outer part just screws on with the nut, backed up the small cable with a few layers of shrink tubing.

The completed male end of the probe lead

On the other end the wires had to be stripped to connect the lead to the coax connector, supplied by me as I replaced the original connectors on the meter when rebuilding it. those male connectors are not available and not included when I bought the meter.

.At first the leads did not work ! Guess what ? The first tech help question “is the unit plugged in” applied. Duh..

Another problem was that on the ACV/ohm , the ohms reading was shorted and not reading. The problem was that the cable braid was shorting to the center conductor after the connector was assembled. I trimmed back the braid, it;s not necessary to connect it at the coax end of the lead.

A final check of the meter was done now and revealed that any AC voltage readings were not properly registering . Ouff! Troubleshooting time. Was the rectifier tube faulty? The tracing reveled an error either in the wiring or a crazy schematic.

Now the time began to fly. Mistakes by tracing the schematic wiring from one page to another lead me down a path that cost time. I pulled the stapled schematic paged apart folded them and joined the pages to indicate the correct path from one page to another. One problem solved. Now a broken wire to nowhere was found from one of the wafers . With the proper tracing, it was discovered that one of the capacitors replaced was in error, going to ground instead of going to the probe connector and to the tube.. Most of the tracing of this device is done by tracing layers of selector switches connected to banks of resistors. Keeping my fingers crossed the meter was plugged in and set to measure AC line voltage. Voila ! Success. Luckily the mistake did not damage the meter when I checked it with 120vac previously.

All in all, including making a cup of coffee break , the bench time was from 13:10 to 18:03 . Taking my pleasurably time with soldering and troubleshooting was worth it. The meter is now ready to go as the humidifier repair is next on the bench.

Now with the purchase and rebuilding of the meter and the probe kit the best part, of course is the use of an analog meter, a Simpson. I would do the required Happy Dance, but I don’t do dances.

1 megohm reading

Final AC line voltage test , before calibration

The coax connections offers better shielding when you need a accurate reading of low ac voltages and the proper isolation for high voltage readings .

5 stars for the kit, those who frequently order parts know the time that’s involved if one had to do all the working ordering all the parts included in this kit.

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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