VIVM?

[RicharD]

Visually Impaired Volt Meter   



I doubt it still works but I do intend to poke around inside and clean thangs up.  The picture doesn't to it justice.  The meter measures 11" corner to corner (like you'd measure a TV).  I picked it up yesterday at the Neon Radio "everything must go" auction.  The auction itself was heart breaking.  It was tough watching all that stuff get sold to 5 old timers, 5 future old timers, and 20 eBayers.

[tubesornothing]

Wow, now that is COOL.

[sluckey]

Haven't seen that name for a loooong time. We had a Hickok tube tester about 25 years ago. Back in the '60s I cut my teeth on a Tek 545 and 585 scope. We also had some Hickok scopes that were identical, even the 545 and 585 model numbers. The timebase and preamp modules would even interchange. The traces on the Hickoks were usually inferior to the Teks though. Just not sharp and too dim on fast timebase. The Hickoks were always the last scopes out of the corral! Later on when I worked in PMEL, I learned to hate trying to calibrate those scopes.

I've never seen a Hickok meter. Looks good on the outside. Wonder if it's a clone too. I think it would be worthwhile to see the needle swing. Good luck.

[tubesornothing]

Betcha the bench moves when you peg the needle.

[PRR]

> VIVM?

It can be very good to have a meter which can be read accurately from the far end of the bench.

> The meter measures 11" corner to corner (like you'd measure a TV).

Measure along the curve, the "scale length". (7 or 8 inch.)

> I doubt it still works

Can't be much wrong with it. "Disasters" would be a failed meter movement or a shattered many-many-pole switch. I would expect it to want a new 20uFd 150V power cap. Do NOT discard the twin-triode; leave it in place until you are sure it is sick (or too brand-valuable to hide in a VTVM). Good VTVMs got a lower-leakage grade of tube from the factory. Any twin-triode has differential drift for the first thousand hours; irrelevant for most work but annoying on a sensitive DC meter.

[RicharD]

So far it appears to work.  There was a 15uf/25v on the back of the meter that had vomited so I replaced it.  There were also 2 D cell batteries that had spilled their guts.  I don't have a 10uF/450V power supply cap so I didn't replace that yet.  I fired it up on a lamp limiter and it's all OK.  Fired it up on it's own and tested the ohms meter.  It's golden.  I found the schematic at good ol BAMA.  I'm fixing to build the ACV probe which uses a 6AL5 and I actually have a NOS one.  No diagram for the DC probe, but I think it's simply a 10M/1M voltage divider.  OH... and I gott scrounge up an old HiZ mic connector and 4 pin screw on barrel connector.

[FYL]

No diagram for the DC probe, but I think it's simply a 10M/1M voltage divider.

It's only a 3.3M series R if I read the schematics correctly.

http://bama.edebris.com/manuals/hickok/209a/
(last page of the docs for the schemo)

[RicharD]

AC probe is done.  About as DIY Jerry Rig as it gets.  The probe housing is 1" EMT.  The probe tip is solid #12 AWG wire.  I used a lot of shrink tubing and electrical tape.  A 3/4" pop in bushing for a stopper and a threaded bushing with a scrap of perf board make up the end stoppers.  I had no luck finding a connector so I fabricated my own with octal pins, an old cardboard cap wrapper, blue tape, & 90 second epoxy.  Not beautiful but it works.... although it's reading 1 volt low.

Time to read the manual and build the DC probe.  I'm going to change the old style mic jack out for a BNC connector (if it'll fit).  Considering changing the skinny old style probe jacks out to regular banana jacks.... in all the fruity colors they come in.

[RicharD]

The DC probe is a series 3.3M resistor.  I had to dime both the AC and DC callibration pots to get the voltages almost correct.  Both read a tad bit low, but close enough for govt. work.  Maybe just maybe a new PS cap will make it happy.  There are 2 other callibration pots but they aren't marked so I'm not twisting them. 

I don't think adding a grounded cord is an option, but a line fuse might be prudent.  The schematic is dated 1940 although I didn't find any dates inside the unit.  I believe the chassis actually needs to float.  The chassis and the ground terminal are bonded.  Looking at secondary AC voltages (hot to hot) might get messy if the unit is earthed.

[PRR]

> I believe the chassis actually needs to float.

I'm not going to read the schematic tonight on a 49K dial-up, but in general:

Safety Standards would now want you to hard-ground it. You can touch it, it better be GROUND.

There's no functional reason to float it. AC reads both ways. Ohms and Cap is always done with the part/device off-wall. I assume it has both DC+ and DC- settings so you can read plate supply or bias supply while leaving the probe shell at case ground.

{whisper} yes, in a few rare cases you do prop it on a phone book, use a ground cheater, and float it. Treat that like changing a receptacle while the breaker is ON: very rarely, reluctantly, carefully. And today, if you "must" take a floating reading, best to use your $9 battery-power DVM and float it.

[PRR]

Missed this:

> Looking at secondary AC voltages (hot to hot) might get messy if the unit is earthed.

Yes, and usually not necessary. Plate and heater windings are usually CT to ground: read each side. For 2-diode DC, the higher AC voltage dominates (though they should be exactly the same). For heater, or 230V motors, add the two 3.2V readings for 6.4V (or 2*115V=230V). If the heater CT is 2*100 ohms, that causes insignificant error against a 10+Meg meter. If there is no heater CT, the meter may ground one side without harm.

Yes, there are reasons to float. I think my 230V well-pump was once connected to two 115V points so that it got.... zero V. Obviously that was not right, so they moved wires until it ran (and never corrected the fusebox markings). For across-the-line work like that, you can use a dumb passive meter, or the DMM cuz it's cheaper today. The VTVM was never the universal meter, nor an electrician's tool, it was the audio/radio workbench meter.

Reading low on most ranges: very low power supply (perhaps the PS cap is shot and it is limping on raw rectified ripple instead of smooth DC), very weak twin-triode, or sick meter. Meters usually work or not, though a 1940 meter may just have a weak magnet.

Check meter: in small print it may say "FS=200uA" or similar. Figure a resistor and 9V battery to make that much current (assume meter resistance is zero, near-enuff). Free the wires from the movement and run your test current through it; does it read full-scale +/-5%?

[RicharD]

I'm going to leave the meter floating.  It's not like this is going to become my main metering device.  It really here just more for show than anything else, much like my very old Heathkit tube signal generator.  It too works, or at least it did last time I fired it up.  I am going to replace the PS cap today just for something to do.