[R-390] R-390A meter substitutes, repair, or sales.

Fri Dec 16 16:58:01 EST 2016

Hello Jacques and many thanks for your helpful message.

The meter I purchased and would like you to check out the pictures posted
with it is eBay item 272446948312.

The one picture I would like you to take a hard look at is the picture that
shows the rear of the meter and what I previously described as a circular
"nut" with four equally spaced square notches. The "nut" is recessed into
the Bakelite surrounding the circular meter case. I am looking for
confirmation (or not) if this "nut" is the key to open up the meter.  Also
am very interested in getting a very "nuts and bolts" specific description
of the technique and tool used to remove the "nut". 

I'm looking forward to your response.

73 / Chris / W7JPG

-----Original Message-----
From: Jacques Fortin [mailto:jacques.f at videotron.ca] 
Sent: Friday, December 16, 2016 11:10 AM
To: R-390 at mailman.qth.net
Cc: 'Chris Kepus'
Subject: RE: [R-390] R-390A meter substitutes, repair, or sales.

Hi Chris,
Your problem is twofold:
1_ How to make "found" meters resemble the original ones (involves
disassembly/reassembly and change of scales).
2_ how to "fit" those in the R-390A circuitry.

The original R-390/R-390A meters are not really "standard".
The Carrier Level meter especially, have quite unusual ratings: Fs = 1mA, Rm
= 17.6 ohms (means a full deflection for 17.6mV across, which denotes a very
sensitive meter - large magnetic field value there).
1mA full scale meters can be easily found (well, have been easily found) but
none of those I run across since the mid-80s were having less than a 50 ohms
Rm, and more currently more (up to 200 ohms).
This means that even if the original meter scale can be replicated and
fitted to one of those "found" meters (which is relatively easy, actually),
they will not perform as intended in the R-390A unless parts values in the
Carrier Level circuitry are modified, OR, if an active "meter adapter"
(using an operational amplifier) is added to the radio.

Another meter rating which was easily found is Fs = 100µA, Rm = 1100 ohms
(means full deflection for 110mV across, so far from the OEM Carrier Meter
value again, but at least this one can be used in the VU Meter position.
"OVU" being 1.228V (+4dBm in 600 ohms) and the normalized VU meter impedance
being 7500 ohms, it means that at a +3 VU reading, it needs 232µA passing
thru.
So a 100µA, 1100 ohms meter will be OK, giving some adaptation (rectifier
bridge needed, calibration of the full scale and of the total impedance,
etc).
The point is that it will be impossible to use a 1mA meter in the VU
position without external amplification/adaptation.

Meter disassembly now: I suspect the meter you describe to be of the "Cosmos
Industries" type.
But just to be sure, can you provide me with a picture of the front and back
of your meter, please ?
These are not too much of a problem to open/reassemble (less than some
hermetically sealed/soldered ones, say...).

And yes, I have a R-390A on which the meters were missing...

73, Jacques, VE2JFE

-----Message d'origine-----
De : R-390 [mailto:r-390-bounces at mailman.qth.net] De la part de Chris Kepus
Envoyé : 16 décembre 2016 10:34 À : 'Bill Riches' <bill.riches at verizon.net>;
R-390 at mailman.qth.net Objet : Re: [R-390] R-390A meter substitutes, repair,
or sales.

Thanks for your response, Bill.  I've got my eye on a couple of eBay meter
prospects but one tends to have greater trust in a known group, hence my ask
about possible spare meters here.

I also acquired a meter that is physically the same size and configuration
but has a white meter face and, of course, the wrong scale, which is why I
am hoping someone will come back with info on how to disassemble these
meters, if possible.

73 / Chris / W7JPG

-----Original Message-----
From: Bill Riches [mailto:bill.riches at verizon.net]
Sent: Friday, December 16, 2016 5:19 AM
To: 'Chris Kepus'; R-390 at mailman.qth.net
Subject: RE: [R-390] R-390A meter substitutes, repair, or sales.

Look on Ebay - there are usually meters there.  Contact the seller and you
may be able to get a matched set.

73,

Bill, WA2DVU

I am rebuilding a R-390A and am in the process of gathering parts while my
back recovers from lumbar fusions and other restorative surgical procedures.
I have another 90 days before I'll be maneuvering this R-390A onto a repair
bench.  

This R-390A is missing it's meters so I am looking for either the real deals
or suitable substitutes.  If anyone has spare working meters that they would
like to convert to wampum, please contact me directly.  

Given the relatively scarcity of these rascals, I have found at least one
candidate for  a substitute meter. It has the same dimensions as the
original meters and when flipped over, it appears to have the same circular
"nut" with four equally spaced square notches and the "nut" is recessed into
the Bakelite surrounding the circular meter case.  

I have never attempted to take one of these meters apart so would someone
who has performed meter surgery please enlighten me if it possible to open
these meters up.  The circular "nut" may not be a nut at all.. But if it is,
it looks like it requires a unique spanner wrench.or ? 

Thanks in advance for any and all input, suggestions, sad tales of meter
destruction, or success stories.

73 / Chris / W7JPG

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