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Antique Electronics Autopsy: 1953 RCA VoltOhmyst

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molear
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Waxed paper parts
molear   3/27/2014 7:09:15 AM
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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
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Re: Waxed paper parts
zeeglen   3/27/2014 9:32:49 AM
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@ 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.

Wnderer
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No Mirror?
Wnderer   3/27/2014 10:23:26 AM
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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
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Re: Waxed paper parts
Caleb Kraft   3/27/2014 10:50:49 AM
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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!

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

Caleb Kraft
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Re: Waxed paper parts
Caleb Kraft   3/27/2014 10:52:47 AM
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@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
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Re: No Mirror?
Wnderer   3/27/2014 10:58:18 AM
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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
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Re: No Mirror?
Caleb Kraft   3/27/2014 11:05:46 AM
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Oh I see! Thanks for the link.

cookiejar
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similar to Heathkit V7-A
cookiejar   3/27/2014 12:15:37 PM
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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.

 

Wnderer
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Re: Waxed paper parts
Wnderer   3/27/2014 1:53:20 PM
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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.

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