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 Post subject: RCA WV-87A Master Voltohmyst
PostPosted: Mar Wed 21, 2012 2:56 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2367
Location: Seattle WA US
First a warning: Don't use alkaline D-cells in this meter. The D-cell is mounted above the power transformer and when the cell leaks, the potassium hydroxide electrolyte will wipe out the transformer as well as other damage. And there seems to be a lot more electrolyte in alkaline cells than in traditional carbon-zinc D-cells.

Now, that the public service announcement is done, does anybody have the calibration instructions for this meter ? I found a minimal schematic online, but nothing else. The circuit is slightly different, with more calibration adjustments than other RCA VTVMs having manuals online.

Thanks for your help,
Chuck K7MCG


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 Post subject: Re: RCA WV-87A Master Voltohmyst
PostPosted: Mar Wed 21, 2012 3:36 am 
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Joined: Jun Sat 09, 2007 8:14 am
Posts: 2079
Location: Florida
How many cal pots does it have? More than a WV-98C (5)?

One way to identify them is to set the meter for a range and then try the pots one at a time until one has an effect. You carefully turn each one a little and if nothing happens set it back and try the next one. I've done this several times over the years.

RRM


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 Post subject: Re: RCA WV-87A Master Voltohmyst
PostPosted: Mar Wed 21, 2012 4:55 pm 
Member

Joined: Feb Thu 24, 2011 1:29 am
Posts: 3021
Location: Dallas, TX - in the city but with bobcats and coyotes
Set mechanical zero first.
Warm-up for 15 minutes.

Current:
Set Selector to "Current" & Range to "50mA". Connect black to -Current and red to +mA.
Deliver exactly 25mA to unit and adjust R14 to half-scale (ed - this is probably a superfluous step)
Deliver exactly 50mA and set R14 for 50mA reading.
Check full-scale of all ranges for +/-3% accuracy.
Move red to +1.5Amp
Supply exactly 1.4 Amperes. Should read between 1.37 and 1.43 A.

DC Voltage:
Selector to "+Volts" Check line voltage for 117V, 60 Hz.
Set Zero Adjust for reading of zero. Do not re-adjust during rest of calibration procedure.
Set Range to "50V". Supply exactly 50 Volts to the ground terminal and probe.
Adjust "+DC Cal," R15, for reading of exactly 50V.
reverse lead connections with selector set to "-Volts."
Adjust "-DC Cal," R13, for a reading of exactly 50 Volts.

AC Calibration Check:
Remove the WG-217 DC Probe from the WG-218 Direct Probe and Cable.
Set Selector to "AC Volts." Set Range to "1.5" Volts.
Short direct probe to ground clip and adjust "AC Zero," R47, for a reading of exactly Zero. This pot is at the rear of chassis and is adjustable via an opening at the rear of the cabinet.
Turn "Range" through the scale settings and verify readings are zero. If not, swap or replace 6AL5s.
Set Range to "150." Apply exactly 150 VAC, 60 Hz, to the direct probe. The meter should read within 5%. If not, verify circuit component values.

AC Compensation Adjustment:
Set the Selector to "AC Volts," & Range to "500V."
Zero pointer (ed - should already be there!)
Apply exactly 200 VAC, at approx. 100 KHz, between Ground and Direct Probe.
Adjust ceramic trimmer C2 for a reading of exactly 200V.


Ohms Adjustment:
Note: Battery must be installed for resistance measurements.
Set Selector to "+Volts" and verify pointer is at zero.
Set Selector to "Ohms" and Range to "RX1."
Adjust the Ohms Adjust for full-scale deflection.
Set Range to "RX1MEG." The meter should read above 1000. A reading of less than 1000 indicates excessive leakage in the resistance circuit.
If necessary to readjust "Ohms Adjust" when changing from RX1 to RX1MEG ranges, verify battery voltage.

I have an original manual to go with mine. :wink:

_________________
In a triode, no one can hear you screen.


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 Post subject: Re: RCA WV-87A Master Voltohmyst
PostPosted: Mar Wed 21, 2012 5:08 pm 
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Joined: Feb Thu 24, 2011 1:29 am
Posts: 3021
Location: Dallas, TX - in the city but with bobcats and coyotes
I would take the time to scan manual and send to somebody IF they would be willing to host it online. 8)

_________________
In a triode, no one can hear you screen.


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 Post subject: Re: RCA WV-87A Master Voltohmyst
PostPosted: Mar Wed 21, 2012 7:39 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 2367
Location: Seattle WA US
Mescalero-
Thank you for taking the time to type out the instructions.
--Chuck K7MCG


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 Post subject: Re: RCA WV-87A Master Voltohmyst
PostPosted: Mar Wed 21, 2012 8:14 pm 
Member

Joined: Feb Thu 24, 2011 1:29 am
Posts: 3021
Location: Dallas, TX - in the city but with bobcats and coyotes
You are welcome. It was a nice lunch-time project for me. I type w/two fingers at my best! :wink:
I really like the blue hammer-tone paint and the big ol' meter face. But, and it's a big but, the battery corrosion can be a beast indeed! :evil:

73 de KB5SHC

_________________
In a triode, no one can hear you screen.


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