From wabate at verizon.net  Mon Aug  7 14:11:11 2023
From: wabate at verizon.net (Bill Abate)
Date: Mon, 7 Aug 2023 14:11:11 -0400
Subject: [Test-Equipment] Simpson 270 VOM
References: <cbc07017-0bdf-5135-ee46-f521015578d0.ref@verizon.net>
Message-ID: <cbc07017-0bdf-5135-ee46-f521015578d0@verizon.net>

Need help on the correct procedure for calibrating my 270.? It started 
with the ohms scale zero adjustment needing to be set at minimum 
resistance with the probes shorted to zero the meter. Batteries are 
fine.? The service info I have indicates there is no adjustment for 
resistance scales.? Traced out the circuit and all resistors are at the 
specified values.? Did a calibration on the 1 ma scale as? the R27 pot 
is in series with the basic movement. That did not help.? The only thing 
left to do is adjust the R32 pot that is across the basic movement.? I 
can't find any info on how to adjust that pot.? My best guess is to use 
it to calibrate the 50 micro amp scale but I'd like confirmation before 
trying that.? When I checked the 50 micro amp scale the specified 
current only showed 44 on the meter..

Thanks,


Bill Abate


From k4pf at juno.com  Mon Aug  7 15:13:10 2023
From: k4pf at juno.com (k4pf at juno.com)
Date: Mon, 7 Aug 2023 19:13:10 GMT
Subject: [Test-Equipment] Simpson 270 VOM
Message-ID: <20230807.151310.15267.0@webmail08.vgs.untd.com>


Hi, Bill

I have a Simpson 270 as well.  
I suppose you have a different series than I do (Series 4, 
about 1975 vintage) since the pot numbers you referenced are different than my schematic.

To calibrate it, you need a 50uA dc current source fed to the 50uA
jack on the front panel, with negative to the common jack.
I would set the range scale on the meter to 500VDC for max isolation
from the remaining terminals during this procedure.
Adjust the pot across the basic meter movement so it reads 
full scale.

Then adjust the pot in series with the basic meter movement 
(using a high impedance voltmeter), so that there is 250mV 
between the 250mV pin and the common pin when the 50uA 
is applied to the pin.

That completes the calibration for DC,
since all your resistors checked OK.

For future reference, if you need to touch up AC calibration,
the pot that connects to the junction of the two diodes
in the AC rectifier is used to adjust the 2.5VAC scale.
The pot connected at the junction between one of the rectifier
diodes and a resistor is then used to trim one of the higher voltage 
AC scales for full-scale calibration with that voltage applied.

I remember calling Simpson around 1999, when I needed 
to recalibrate my 270, and realized the info wasn't in the manual.
The woman on the phone said "Our calibration procedures
are for our technicians."  I eventually found the info
I needed on line, in a military tech manual.

73,
Ed Knobloch

> Bill Abate wrote:
Need help on the correct procedure for calibrating my 270.
It started with the ohms scale zero adjustment 
needing to be set at minimum resistance with the probes 
shorted to zero the meter. Batteries are fine.? 
The service info I have indicates there is no adjustment 
for resistance scales.? Traced out the circuit and all resistors 
are at the specified values.? Did a calibration on the 1 ma scale as the R27 pot is in series with the basic movement. 
That did not help.? The only thing 
left to do is adjust the R32 pot that is across the basic movement.? I can't find any info on how to adjust that pot. My best guess 
is to use it to calibrate the 50 micro amp scale but I'd like confirmation before trying that.? 
When I checked the 50 micro amp scale the specified 
current only showed 44 on the meter..



From k4pf at juno.com  Mon Aug  7 22:38:52 2023
From: k4pf at juno.com (k4pf at juno.com)
Date: Tue, 8 Aug 2023 02:38:52 GMT
Subject: [Test-Equipment] Simpson 270 VOM
Message-ID: <20230807.223852.18462.1@webmail08.vgs.untd.com>



Hi, Bill

On my 270 series 4, the 50uA jack is also labeled as a 250mV pin.
It's the equivalent, for a 20K Ohms/Volt movement.

If you divide 250mV by 50uA, you get 5K Ohms.
So a quarter volt full scale would see a 5K resistance load.
Therefore, a one volt scale would be 20K Ohms total resistance.

I see for the 270 original model, and for the 270 series 2 and 3,
 they didn't label that jack both 50uA as well as 250mV,
they only labeled it 50uA.  But it serves the same function.

We can create a 50uA current source using a 5V power supply
in series with 95K resistor.  That will be the correct
current assuming a 5K load by the meter.  There may be a slight
back-and-forth adjustment as you trim the series pot to get 0.25VDC
between the 50uA jack and the common jack, and may need to touch
up the pot across the meter movement to maintain full scale.

Something like a 10Meg Ohm input DMM would be ideal 
to measure the 250mV drop, without disturbing the Simpson
calibration. 10Meg in parallel with 5K is a negligible error.

73,
Ed Knobloch  K4PF


> Bill Abate wrote:
Thanks for the info.  I hope the recal helps the ohms zero problem.
I found a military manual, TB 9-6625-2352-35, for the Simpson meter 
service, but I did not find the info that you provided.  One thing is 
confusing me, I can't follow what you are calling the 250MV pin.  Where is that?  The calibration that I have for the meter series pot is for the 1 ma scale.

From k4pf at juno.com  Fri Aug 11 14:37:05 2023
From: k4pf at juno.com (k4pf at juno.com)
Date: Fri, 11 Aug 2023 18:37:05 GMT
Subject: [Test-Equipment] Simpson 270 VOM
Message-ID: <20230811.143705.19932.0@webmail08.vgs.untd.com>


Hi, Bill

To follow up our discussion on the Simpson 270 calibration -

I looked at the military manual you referenced, TB 9-6625-2352-35.
At the bottom of page 13, in the procedure for the Simpson
model 260 series 3, they explain how the 50uA jack 
is also the 250mV jack in footnote 2.

One error in the chart is that they lead off with '250'
at the top of their voltage chart.  It should be labeled 250mV.

The adjustment for 250mV is also relied on for the current metering
function. The current shunts have 250mV voltage drop 
across them for full scale reading.  Unless that series pot 
is first adjusted for 250mV with 50uA applied, all the current
readings will be off. 

My method, using a 5V supply with a 95K series resistor allows 
both the 50uA and 250mV adjustments to be done simply,
using one set-up.  Of course, you could use a different supply
voltage, requiring a different resistor than 95K,
but I assume everyone has a regulated 5V supply handy.
Just don't forget to account for the 5K resistance of the basic
movement and its adjustment pots.

You never mentioned what series 270 you have, so I couldn't
reference the pots by number for your unit.  

If you download a 270 series 4 manual, the 50uA current adjust pot
across the meter movement is R1.  The pot in series with the meter
movement to adjust the 250mV setting is R2.

73,
Ed

> Bill Abate wrote:
Thanks for the info.  I hope the recal helps the ohms zero problem.
I found a military manual, TB 9-6625-2352-35, for the Simpson meter 
service, but I did not find the info that you provided.  One thing is 
confusing me, I can't follow what you are calling the 250MV pin.  Where is that?  The calibration that I have for the meter series pot is for the 1 ma scale.


From w5jv at hotmail.com  Sun Aug 13 12:14:20 2023
From: w5jv at hotmail.com (Doug Hensley)
Date: Sun, 13 Aug 2023 16:14:20 +0000
Subject: [Test-Equipment] Need PDF Manual for Sencore's DVM56A
In-Reply-To: <SA0PR19MB4409FADFB3B092CBFCA15B219116A@SA0PR19MB4409.namprd19.prod.outlook.com>
References: <SA0PR19MB4409FADFB3B092CBFCA15B219116A@SA0PR19MB4409.namprd19.prod.outlook.com>
Message-ID: <SA0PR19MB4409BC65A084D98834FAF2C59116A@SA0PR19MB4409.namprd19.prod.outlook.com>

Can anyone send me a pdf file on the Sencore DVM56A?

BAMA does not have it.

Thank you,

Doug W5JV





Visit https://www.qrz.com/db/W5JV for some great vacuum tube finds.



From larry41gm at gmail.com  Sun Aug 27 08:27:36 2023
From: larry41gm at gmail.com (Larry H)
Date: Sun, 27 Aug 2023 05:27:36 -0700
Subject: [Test-Equipment] [R-390] Fair Radio Sales closing in a few
	months!
In-Reply-To: <CAOQ84ats_M2feWw6FLJVYr3knBmmVC6BgEjTAyMeojo9XRkmyA@mail.gmail.com>
References: <CAOQ84ats_M2feWw6FLJVYr3knBmmVC6BgEjTAyMeojo9XRkmyA@mail.gmail.com>
Message-ID: <CAOSJ_nt-EW6Xj9__0CE-mWokcc4CyCggbLY=Umi=zVPvZaua_g@mail.gmail.com>

Hi All,  If they close, it would be a very sad day indeed, for the 'boat
anchor' community.  It would be the end of an era, as they have supplied us
with a considerable variety of equipment and parts over the many years.  I
will miss them.

Regards, Larry
------------------------------------------------------------------------------------------------------------------------------------------------------------

On Mon, Aug 21, 2023 at 9:56?AM Paul Staupe <staupe at gmail.com> wrote:

> My FL-101 AC line filter shorted out during a move a few weeks ago so I
> called Fair Radio and in talking to Paul, he said that they're closing the
> doors for good in a couple of months.  Owner has finally decided to retire.
>
> Hope someone in this group can make them an offer,  otherwise get your
> R-3xx parts ASAP!
>
> Best regards,
>
> Paul W0AD
> Minneapolis
> ______________________________________________________________
> R-390 mailing list
>

From w5jv at hotmail.com  Mon Aug 28 15:48:19 2023
From: w5jv at hotmail.com (Doug Hensley)
Date: Mon, 28 Aug 2023 19:48:19 +0000
Subject: [Test-Equipment] WTB: PAIR OF VINTAGE TEST LEADS WITH THE SMALL TIP
 PLUGS (LIKE WW2 ERA)
Message-ID: <SA0PR19MB44098A8D70B637DF75A7CE6C91E0A@SA0PR19MB4409.namprd19.prod.outlook.com>

I'm looking for a pair of simple red/black test leads to use with an old 1940's-50's VOM
which has the small + & -  sockets.  Looks like 1/16" or 2 mm ??

If anyone has a spare they can sell.  Please QSL.

Thanks


Doug W5JV





Visit https://www.qrz.com/db/W5JV for some great vacuum tube finds.



From k4pf at juno.com  Mon Aug 28 21:07:26 2023
From: k4pf at juno.com (k4pf at juno.com)
Date: Tue, 29 Aug 2023 01:07:26 GMT
Subject: [Test-Equipment] WTB: PAIR OF VINTAGE TEST LEADS WITH THE SMALL
	TI	P PLUGS (LIKE WW2 ERA)
Message-ID: <20230828.210726.2158.2@webmail08.vgs.untd.com>


Hi, Doug -
It looks like this would work:
https://www.ebay.com/itm/254357170058


I have a set from another seller, and it plugs fine business into
an original series Simpson 269 VOM female pin connector.

73,
Ed Knobloch  K4PF


>
I'm looking for a pair of simple red/black test leads to use with an old 1940's-50's VOM
which has the small + & -  sockets.  Looks like 1/16" or 2 mm ??

If anyone has a spare they can sell.  Please QSL.

Thanks


Doug W5JV

I'm looking for a pair of simple red/black test leads to use with an old 1940's-50's 
VOM
which has the small + & -  sockets.  Looks like 1/16" or 2 mm ??

If anyone has a spare they can sell.  Please QSL.

Thanks


Doug W5JV


I'm looking for a pair of simple red/black test leads to use with an old 1940's-50's VOM
which has the small + & -  sockets.  Looks like 1/16" or 2 mm ??

If anyone has a spare they can sell.  Please QSL.

Thanks


Doug W5JV





Visit https://www.qrz.com/db/W5JV for some great vacuum tube finds.


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From w5jv at hotmail.com  Tue Aug 29 09:54:01 2023
From: w5jv at hotmail.com (Doug Hensley)
Date: Tue, 29 Aug 2023 13:54:01 +0000
Subject: [Test-Equipment] WTB: PAIR OF VINTAGE TEST LEADS WITH THE SMALL
 TIP PLUGS (LIKE WW2 ERA)
In-Reply-To: <SA0PR19MB44098A8D70B637DF75A7CE6C91E0A@SA0PR19MB4409.namprd19.prod.outlook.com>
References: <SA0PR19MB44098A8D70B637DF75A7CE6C91E0A@SA0PR19MB4409.namprd19.prod.outlook.com>
Message-ID: <SA0PR19MB44090A5C36D5F4633D2AE8AE91E7A@SA0PR19MB4409.namprd19.prod.outlook.com>

Bingo.  It looks like the Pomona 1432 (banana plug to pin plug adapter) is the way to go.

Many thanks for all the replies.  Great group.

Doug W5JV








________________________________
From: Doug Hensley
Sent: Monday, August 28, 2023 2:48 PM
To: boatanchors mailman.qth.net <boatanchors at mailman.qth.net>; hallicrafters at mailman.qth.net <hallicrafters at mailman.qth.net>; heathkit at mailman.qth.net <heathkit at mailman.qth.net>; test-equipment at mailman.qth.net <test-equipment at mailman.qth.net>
Subject: WTB: PAIR OF VINTAGE TEST LEADS WITH THE SMALL TIP PLUGS (LIKE WW2 ERA)

I'm looking for a pair of simple red/black test leads to use with an old 1940's-50's VOM
which has the small + & -  sockets.  Looks like 1/16" or 2 mm ??

If anyone has a spare they can sell.  Please QSL.

Thanks


Doug W5JV





Visit https://www.qrz.com/db/W5JV for some great vacuum tube finds.



From k4pf at juno.com  Tue Aug 29 11:45:24 2023
From: k4pf at juno.com (k4pf at juno.com)
Date: Tue, 29 Aug 2023 15:45:24 GMT
Subject: [Test-Equipment] WTB: PAIR OF VINTAGE TEST LEADS WITH THE SMALL
	TI		P PLUGS (LIKE WW2 ERA)
Message-ID: <20230829.114524.31313.0@webmail04.vgs.untd.com>


POSSIBLE CORRECTION

I took another look at the photos of test leads offered on eBay -
I first thought that the end of the leads closest to the meter
jack were pin type connectors plugged into their recepticles,
but I may be wrong.  They may be permanent connectors,
not a plug and jack assembly as I assumed.
The military serial numbers on the two probes do match my
(correct) set I use with the old Simpson 269.

Sorry for any confusion.

Ed  K4PF

<<my <original email>>
Hi, Doug -
It looks like this would work:
https://www.ebay.com/itm/254357170058

I have a set from another seller, and it plugs fine business into
an original series Simpson 269 VOM female pin connector.

73,
Ed Knobloch  K4PF


>
I'm looking for a pair of simple red/black test leads to use with an old 1940's-50's VOM
which has the small + & -  sockets.  Looks like 1/16" or 2 mm ??

If anyone has a spare they can sell.  Please QSL.

Thanks


Doug W5JV



