[R-390] 390A Line Level meter replacement..?

[Bob Weiss]

I still have a few of the opamp PCBs I manufactured for converting ordinary
panel meters for use in the R-390 carrier circuit. Info in thread here:

https://live.staticflickr.com/1722/41820958175_fe8d826471.jpg

Picture here:
https://live.staticflickr.com/1722/41820958175_fe8d826471.jpg

73,
Bob Weiss N2IXK

On Wed, Nov 3, 2021 at 1:49 PM Jim Whartenby via R-390 <
r-390 at mailman.qth.net> wrote:

> David and the group
> I have successfully used Pete Williams' meter modification published on
> the Milsurplus list back in June of 2006.  I see that you and Dave assisted
> Pete in fleshing out this modification.  For everyone else, here it is in
> Pete's own words:
>
> "HiWhile some of you guys have been getting legless from taking the plate
> caps off 807's, some of us at the other end of the  day have been active in
> being practical in adapting surplus meters for the carrier level function
> in R-390A.
>
> The original meter has an internal R of around 10 Ohms and the replacement
> meter I have (ex W5cab) has an Internal R of around 103 ohms.  It has a
> FSD of 1 mA.  The scale plate changed per foto details available on the net.
>
> Altho' it deflects, the reading is a fraction of the original.  Following
> suggestions made by David Wise and Gary Gitzen,modifications made to the
> meter bridge circuit gave identical results to that generated with original
> meters.
>
> Not only was meter deflection approximately the same (Even readings from
> original meters varied under same test  conditions) but the parameters of
> linearity and AGC also remained identical to readings obtained with the
> original meters during the tests.  Time constant values also appeared to be
> the same as original.
>
> MODIFICATION.  Refer to Fig 22 on page 36 of manual TM 11-5820-358-35.
> Replace R524 with a 600 ohm resistor.
> Replace R548  with a 160ohm resistor.  Both are easy to get at.
> Remove R537 a 22 ohm resistor from the  carrier meter adjust pot.
> Remove the shorting link from the center wiper terminal of this pot and
> connect the white - blue - orange wire to the  "hot end" of the pot.
> The  white - blue - green wire stays on the center wiper and it is already
> connected to the + side of meter M102.  The  white  wire stays going to
> chassis.
> Zero the meter as per the manual and that's it.
>
> NOTE:  Other meters of greatly differing IR's may require modification of
> the resistor values.  None were available fortest.
> Thanks to Dave and Gary for interest and assistance with these
> modifications.
> Purists can get on with evacuating 807's!
>
> Cheers
> Pete D . Williams
> METUNG 3904
> Australia
> jupete at bigpond.net.au"
>
> I always enjoyed Pete's posts, as you can see, he was a character!   He
> and Nolan Lee made quite a few posts that were both informative and a joy
> to read.  I miss them both.
>
> The meters I have used in the above modification came from perhaps a half
> dozen SRR-13's and FRR-23's that I got at a local estate auction many years
> ago.  I believe that all of the radios at this auction came from the estate
> of Dr James Black but W5OR certainly has a better memory of this then I
> do.  Most of these radios were damaged in a fire, some scorched, some with
> smoke and fire extinguisher residue.  The VU meter was a drop-in
> replacement, the Carrier Level meter responded well to the above mod.
>
> Let's hope that I have properly formatted the above so that it is
> readable.  I think that this list does not like my browser!
>
> Regards,
> Jim
> Too much agreement kills a chat.  E. Cleaver
>
> -----Original Message-----
> From: David Wise <David_Wise at Phoenix.com>
> To: Jacques Fortin <jacques.f at videotron.ca>; 'Jordan Arndt' <
> Outposter30 at shaw.ca>; 'R-390 Forum' <r-390 at mailman.qth.net>
> Sent: Wed, Nov 3, 2021 10:53 am
> Subject: Re: [R-390] 390A Line Level meter replacement..?
>
> Gary Gitzen and I developed a fairly simple IF deck mod that allows use of
> virtually any 1mA or smaller meter movement for the Carrier function.  No
> op-amp required.  The mod also improves the action of the Carrier Zero
> adjuster.  I believe it's in the Pearls of Wisdom archive.
>
> Dave Wise
> SWL (inactive)
>
> From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
> On Behalf Of Jacques Fortin
> Sent: Wednesday, November 03, 2021 7:46 AM
> To: 'Jordan Arndt'; 'R-390 Forum'
> Subject: Re: [R-390] 390A Line Level meter replacement..?
>
> Hello Jordan,
>
> Wow ! Good find !
> If only there are also some matching style 1mA fs, 18 ohms meters with a
> 0-100 dB dial for the RF Level, now...
> But OK, I am asking too much...
> Let us know how they work when you will have those in hand !
>
> 73, Jacques, VE2JFE
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