Breaking News
The Engineering Life - Around the Web

Antique Electronics Autopsy: 1953 RCA VoltOhmyst

NO RATINGS
Page 1 / 3 Next >
View Comments: Threaded | Newest First | Oldest First
molear
User Rank
Rookie
Waxed paper parts
molear   3/27/2014 7:09:15 AM
NO RATINGS
The parts in waxed paper are NOT resistors.  Those would be capacitors, and I would be very careful using that device.  The old paper and wax capacitors can go bad.  I've had one explode and blast scraps of burning paper around the room.

zeeglen
User Rank
Blogger
Re: Waxed paper parts
zeeglen   3/27/2014 9:32:49 AM
NO RATINGS
@ Caleb - Why wax sleeves over the resistors?  Might this be intended as an indication of overheating if a user applies a higher-than-rated voltage, or any voltage with the function switch set to "ohms"?

@ molear - looking at the schematic and parts list these are 1% resistors, there are only 3 wax paper caps listed.

Caleb Kraft
User Rank
Blogger
Re: Waxed paper parts
Caleb Kraft   3/27/2014 10:52:47 AM
NO RATINGS
@zeeglen, I have no idea why they would be wax covered. I was hoping someone would give a valid explanation in the comments. I'm guessing it is shielding of some type, but is wax paper that effective?

Wnderer
User Rank
CEO
Re: Waxed paper parts
Wnderer   3/27/2014 1:53:20 PM
NO RATINGS
More memories from high school.

I recall they used to make precision values of resistors by filing them. They may be using the wax to protect the ground sections after setting the value. I'm not sure about this, though.

Caleb Kraft
User Rank
Blogger
Re: Waxed paper parts
Caleb Kraft   3/27/2014 10:50:49 AM
NO RATINGS
I can understand your confusion. This is not a typical thing to see. Usually, only capacitors would carry that waxy coating. however, in this case, those are resistors. You can see it in the schematic as well as just figure it out by looking at what the mode selector that they are attached to does. it changes the resistance!

herbissimus
User Rank
Rookie
Re: Waxed paper parts
herbissimus   3/27/2014 7:22:44 PM
NO RATINGS
those of us, for most if not all measurements lived in a world of plus or minus ten percent. mirror not necessary. as to only $15.oo : minimum wage was less than 1 dollar. i couldn't afford a new one. today any autoparts store's got one for $10-$30 that can measure to 1% and has a pretty good repeatability and runs on batteries which vtvm's did not, usually.

Wnderer
User Rank
CEO
No Mirror?
Wnderer   3/27/2014 10:23:26 AM
NO RATINGS
I think it's strange that it doesn't have a mirror. I thought even the cheap ones had a mirror to deal with parallax.

Caleb Kraft
User Rank
Blogger
Re: No Mirror?
Caleb Kraft   3/27/2014 10:51:38 AM
NO RATINGS
I'm not sure what you're referring to, but now I'm really curious!

Wnderer
User Rank
CEO
Re: No Mirror?
Wnderer   3/27/2014 10:58:18 AM
NO RATINGS
Here's a link.

http://www.radio-electronics.com/info/t_and_m/analogue-multimeter-voa-vom/how-to-use-using-analog-meter.php

 

I was taught in high school to use these meters. You line up the needle with the one in the mirror to get an accurate reading.

Caleb Kraft
User Rank
Blogger
Re: No Mirror?
Caleb Kraft   3/27/2014 11:05:46 AM
NO RATINGS
Oh I see! Thanks for the link.

cookiejar
User Rank
Manager
similar to Heathkit V7-A
cookiejar   3/27/2014 12:15:37 PM
NO RATINGS
I still have my Heathkit V7-A VTVM which I built in 1957 working.  It's a close cousin to the RCA who had all the standard tube circuits in their tube manuals.  The Heathkit has a db scale and no separate scale for the 1.5V range.  In the 60s I replaced the 1.5V D cell for the ohms function with a power supply kit sold for that function and the zero and ohms pots with the vernier (planetary ball) pots availble from Heath which made setting zero and ohms far less touchy.

Those wax covered paper tubes are hiding the reistor values underneath them.  Who knows what purpose they serve. If you look at the schematic, there are very few caps in the circuit. 

I'm impressed that all my Heathkit tube equipment from the 50s and 60s still functions very well indeed. The only repair I've had to do is replace a resistor in the AG-9A audio generator which had too low a wattage rating causing value shift and 4% harmonic distortion.  After that fix the distortion went down to under 0.02%.

I still mourn the death of Heathkit, like a long lost friend.  They got me into electronics after all.

 

Rocket_G
User Rank
Rookie
Re: similar to Heathkit V7-A
Rocket_G   3/28/2014 9:12:39 PM
NO RATINGS
Cool! As a teenager I built a Heathkit IM-11 back in the 1960's, learned a lot about vacuum tube circuits from the build, and got lots of use out of it.  The RCA VoltOhmyst looked familiar to me as well.  Sometime in my undergrad years (B.S.E.E.) I gave it away to an aspiring young EE.

Susan Rambo
User Rank
Blogger
Senior citizen?
Susan Rambo   3/29/2014 2:51:46 PM
NO RATINGS
Caleb, why do they call it "senior"?

Caleb Kraft
User Rank
Blogger
Re: Senior citizen?
Caleb Kraft   3/30/2014 5:38:19 PM
NO RATINGS
I believe there is a Jr. Version that is not as fancy.

MeasurementBlues
User Rank
Blogger
The beauty of old test equipment
MeasurementBlues   4/1/2014 9:47:52 AM
NO RATINGS
Dedicated knobs, no menus, easier to fix. No software. OK you don't get PC connectivity. Life is a tradeoff.

MeasurementBlues
User Rank
Blogger
Old test equipment and a future engineer
MeasurementBlues   4/1/2014 9:50:18 AM
NO RATINGS
See Vintage test equipment: Not just for old engineers where I give a firsthand look at a high-school student's collection of vintage test equipment.

Flash Poll
Radio
LATEST ARCHIVED BROADCAST
Join our online Radio Show on Friday 11th July starting at 2:00pm Eastern, when EETimes editor of all things fun and interesting, Max Maxfield, and embedded systems expert, Jack Ganssle, will debate as to just what is, and is not, and embedded system.
Like Us on Facebook

Datasheets.com Parts Search

185 million searchable parts
(please enter a part number or hit search to begin)
EE Times on Twitter
EE Times Twitter Feed
Top Comments of the Week