Posts: 10
Threads: 2
Joined: Nov 2022
City: Placentia
State, Province, Country: CA
The Model 84 (1934 or so) I'm restoring has a nice table of various typical voltages in the unit. It calls out the Philco Model 048 All-Pupose Set Tester as the meter to use.
I have no doubt the Ohms per Volt of the meter is a much lower value than modern meters. Anyone have a clue of what the Ohms per Volt DC meter on this unit would be?
Maybe 1000 Ohms / Volt? 5000 OHMS per Volt? 10K ohms / Volt?
I have seen those (and others) on meters in that generation. I know I can put an appropriate resistor across the leads of a modern volt meter, but the question is what resistor value?
Thanks.
Klemer
(This post was last modified: 11-24-2022, 05:22 PM by
klemer.)
Posts: 7,212
Threads: 266
Joined: Dec 2009
City: Roslyn Pa
Hi and welcome,
On the 025 Circuit Tester there's a slim chance that it's a battery powered vtvm. In that case it would be 1megohm. The reason I mention it is that it has an off position on one of the controls. If it isn't a vtvm it's probably 1k per volt. I couldn't find a diagram of it. There's ad in the 1936 parts catalogue pg 24 near the bottom. If you have a burning desire to acquire one there's one on epay.
A good decently calibrated vtvm is handy tool to have on your service bench. It's great for aiding in alignments and won't load down control grid voltages when measuring like vom will. In general if the measured voltage is within about 20% with a modern device it's a good starting point nowdays. Vacuum tube circuits are a lot more forgiving than solid state devices. 1/2 or 1 volt on the base or emitter of a transistor can make the difference between it being turn on and working or off and dead.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
Posts: 10
Threads: 2
Joined: Nov 2022
City: Placentia
State, Province, Country: CA
Thanks, Radioroslyn. After further reading and remembering what I had read years ago, I think this issue is no big deal at the moment. In the range of the voltages I'm measuring at present (250+ VDC), I don't think it really matters what the ohms/volts is. I would be willing surprised if the Philco model 048 tester that Philco Model 84 "specifies" was a VTVM, but I guess it's possible. In any case, even if it was 1000 ohms/volt, the difference would be small enough that I can ignore it. I seem to collect test equipment, and have about 10 meters of various types, from the new variety Fluke, back to some neat ones around the late 1930's or so. Unfortunately, none are 1000 ohms per volt. A bigger problem in my recently refurbed Model 84 is some DC voltages that are 260VDC when they are supposed to be 225VDC, according to Philco data. The radio works fine, very nice reception for a 4 tuber, after I re-wound the antenna coil! But I'm afraid of the lifetime of tubes with screens 30VDC over the tube spec. I'm starting to suspect the previously replaced transformer... Sorry to hijack the thread!
Thanks again!
