Empathy List Archives

DC

David C. Partridge

Thu, Oct 16, 2025 12:41 PM

I am trying to calibrate a Solartron 7071 I've been working on.

I set the calibrator to 800V and issued the command:
calibrate,vdc=1000,high=800
but part way through the calibrator went into overload (too much current
drawn).

The calibrator doesn't go into overload when feeding the 3458A.

The calibrate command finished, but now the meter is behaving oddly.

With input values up to 14V DC the correct value is displayed. If I
increase the value above there, I get:

           Input                     Display

15V 1134.061

16V 1209.664

17V 1285.276

18V 1360.867

19V 1436.474 OVERLOAD

calibrate,dump

OK

Vdc calibration constants

-1.78813934E-06

164.781288E-03

-2.92062759E-06

1.64774580E+00

-1.66893005E-06

16.4787127E+00

-2.14576721E-06

164.788683E+00

-2.68220901E-06

1.64800913E+03

Vac calibration constants

326.985921E-03

3.27081809E+00

32.5331218E+00

325.456807E+00

3.27348303E+03

kOhm calibration constants

-1.78813934E-06

166.021009E-03

-2.92062759E-06

1.66000890E+00

-1.66893005E-06

16.6035262E+00

-2.92062759E-06

165.948071E+00

-1.66893005E-06

1.65979766E+03

Top Ohms range calibration constants

-1.66893005E-06

10.0332974E+03

602.359830E-03

Ratio terminals calibration constant

16.4792383E+00

Zener current token value

085

Reading that suggests the the 1000V high calibration factor appears
to be in the right "ball park" - confirmation would be good
Any suggestions on what's gone awry with the autorange?
How to track down the problem that's causing the calibrator
overload.

Has anyone been there, done that? Any suugestions welcome.

Cheers, David

I am trying to calibrate a Solartron 7071 I've been working on. I set the calibrator to 800V and issued the command: calibrate,vdc=1000,high=800 but part way through the calibrator went into overload (too much current drawn). The calibrator doesn't go into overload when feeding the 3458A. The calibrate command finished, but now the meter is behaving oddly. With input values up to 14V DC the correct value is displayed. If I increase the value above there, I get: Input Display 15V 1134.061 16V 1209.664 17V 1285.276 18V 1360.867 19V 1436.474 OVERLOAD calibrate,dump OK Vdc calibration constants -1.78813934E-06 164.781288E-03 -2.92062759E-06 1.64774580E+00 -1.66893005E-06 16.4787127E+00 -2.14576721E-06 164.788683E+00 -2.68220901E-06 1.64800913E+03 Vac calibration constants 326.985921E-03 3.27081809E+00 32.5331218E+00 325.456807E+00 3.27348303E+03 kOhm calibration constants -1.78813934E-06 166.021009E-03 -2.92062759E-06 1.66000890E+00 -1.66893005E-06 16.6035262E+00 -2.92062759E-06 165.948071E+00 -1.66893005E-06 1.65979766E+03 Top Ohms range calibration constants -1.66893005E-06 10.0332974E+03 602.359830E-03 Ratio terminals calibration constant 16.4792383E+00 Zener current token value 085 1. Reading that suggests the the 1000V high calibration factor appears to be in the right "ball park" - confirmation would be good 2. Any suggestions on what's gone awry with the autorange? 3. How to track down the problem that's causing the calibrator overload. Has anyone been there, done that? Any suugestions welcome. Cheers, David

DC

David C. Partridge

Thu, Oct 16, 2025 2:54 PM

Further information

If I switch to the 100V range manually, then I can increase the input
voltage up to 142V without triggering any "odd" results.
If I switch to the 1000V range manually, then I can increase the input
voltage up to 310V or so without triggering an error (the actual voltage at
which it goes silly varies).

David

Further information If I switch to the 100V range manually, then I can increase the input voltage up to 142V without triggering any "odd" results. If I switch to the 1000V range manually, then I can increase the input voltage up to 310V or so without triggering an error (the actual voltage at which it goes silly varies). David

DC

David C. Partridge

Fri, Oct 17, 2025 10:23 AM

Looks like RL5 in the input attenuator circuit isn't opening fully, so above
a certain voltage it lets the voltage on its input through to the input of
DC ranging circuit.

It is a Coto 3400-0051. I can't find any information about that so don't
know a suitable replacement.

Does anyone have either a) any of these relays to spare, or b) know of a
replacement?

Thanks
David

Looks like RL5 in the input attenuator circuit isn't opening fully, so above a certain voltage it lets the voltage on its input through to the input of DC ranging circuit. It is a Coto 3400-0051. I can't find any information about that so don't know a suitable replacement. Does anyone have either a) any of these relays to spare, or b) know of a replacement? Thanks David

D

DM

Fri, Oct 17, 2025 4:16 PM

David,
The Coto 3400 Series relays were low thermal EMF relays. I've attached a PDF of some pages from old EEM catalogs (the Internet Archive has them for download). Sketchy information at best; I haven't found a catalog of the complete 3400 series relays. Coto still produces low thermal EMF relays in the 3500 & 3600 series. Don't know if either of these would be a good fit for your instrument, or if they're available from any of the usual suppliers.
You didn't describe your relay as to form factor, coil & contact arrangements, but there are several Coto 3400 series relays listed on Ebay. With a little Yankee Ingenuity, maybe one of them could be adopted by your insrument.
Good luch with your search.
David Mason
Alabama, USA

----- Original Message -----
From: "David C. Partridge via volt-nuts" volt-nuts@lists.febo.com
To: "Discussion of precise voltage measurement" volt-nuts@lists.febo.com
Cc: "David C. Partridge" david.partridge@perdrix.co.uk
Sent: Friday, October 17, 2025 5:23:01 AM
Subject: [volt-nuts] Re: Problem with Solartron 7071

Looks like RL5 in the input attenuator circuit isn't opening fully, so above
a certain voltage it lets the voltage on its input through to the input of
DC ranging circuit.

It is a Coto 3400-0051. I can't find any information about that so don't
know a suitable replacement.

Does anyone have either a) any of these relays to spare, or b) know of a
replacement?

Thanks
David

volt-nuts mailing list -- volt-nuts@lists.febo.com -- To unsubscribe send an email to volt-nuts-leave@lists.febo.com
To unsubscribe, go to and follow the instructions there.

David, The Coto 3400 Series relays were low thermal EMF relays. I've attached a PDF of some pages from old EEM catalogs (the Internet Archive has them for download). Sketchy information at best; I haven't found a catalog of the complete 3400 series relays. Coto still produces low thermal EMF relays in the 3500 & 3600 series. Don't know if either of these would be a good fit for your instrument, or if they're available from any of the usual suppliers. You didn't describe your relay as to form factor, coil & contact arrangements, but there are several Coto 3400 series relays listed on Ebay. With a little Yankee Ingenuity, maybe one of them could be adopted by your insrument. Good luch with your search. David Mason Alabama, USA ----- Original Message ----- From: "David C. Partridge via volt-nuts" <volt-nuts@lists.febo.com> To: "Discussion of precise voltage measurement" <volt-nuts@lists.febo.com> Cc: "David C. Partridge" <david.partridge@perdrix.co.uk> Sent: Friday, October 17, 2025 5:23:01 AM Subject: [volt-nuts] Re: Problem with Solartron 7071 Looks like RL5 in the input attenuator circuit isn't opening fully, so above a certain voltage it lets the voltage on its input through to the input of DC ranging circuit. It is a Coto 3400-0051. I can't find any information about that so don't know a suitable replacement. Does anyone have either a) any of these relays to spare, or b) know of a replacement? Thanks David _______________________________________________ volt-nuts mailing list -- volt-nuts@lists.febo.com -- To unsubscribe send an email to volt-nuts-leave@lists.febo.com To unsubscribe, go to and follow the instructions there.

DC

David C. Partridge

Tue, Oct 21, 2025 4:48 PM

I've checked and I think that a 3602-05-52 is a good replacement. Not cheap mind you ☹

Coto of course didn't reply to my enquiry ☹

David

-----Original Message-----
From: DM via volt-nuts volt-nuts@lists.febo.com
Sent: 17 October 2025 17:17
To: Discussion of precise voltage measurement volt-nuts@lists.febo.com
Cc: DM dgminala@mediacombb.net
Subject: [volt-nuts] Re: Problem with Solartron 7071

David,
The Coto 3400 Series relays were low thermal EMF relays. I've attached a PDF of some pages from old EEM catalogs (the Internet Archive has them for download). Sketchy information at best; I haven't found a catalog of the complete 3400 series relays. Coto still produces low thermal EMF relays in the 3500 & 3600 series. Don't know if either of these would be a good fit for your instrument, or if they're available from any of the usual suppliers.
You didn't describe your relay as to form factor, coil & contact arrangements, but there are several Coto 3400 series relays listed on Ebay. With a little Yankee Ingenuity, maybe one of them could be adopted by your insrument.
Good luch with your search.
David Mason
Alabama, USA

----- Original Message -----
From: "David C. Partridge via volt-nuts" volt-nuts@lists.febo.com
To: "Discussion of precise voltage measurement" volt-nuts@lists.febo.com
Cc: "David C. Partridge" david.partridge@perdrix.co.uk
Sent: Friday, October 17, 2025 5:23:01 AM
Subject: [volt-nuts] Re: Problem with Solartron 7071

Looks like RL5 in the input attenuator circuit isn't opening fully, so above a certain voltage it lets the voltage on its input through to the input of DC ranging circuit.

It is a Coto 3400-0051. I can't find any information about that so don't know a suitable replacement.

Does anyone have either a) any of these relays to spare, or b) know of a replacement?

Thanks
David

volt-nuts mailing list -- volt-nuts@lists.febo.com -- To unsubscribe send an email to volt-nuts-leave@lists.febo.com To unsubscribe, go to and follow the instructions there.

I've checked and I think that a 3602-05-52 is a good replacement. Not cheap mind you ☹ Coto of course didn't reply to my enquiry ☹ David -----Original Message----- From: DM via volt-nuts <volt-nuts@lists.febo.com> Sent: 17 October 2025 17:17 To: Discussion of precise voltage measurement <volt-nuts@lists.febo.com> Cc: DM <dgminala@mediacombb.net> Subject: [volt-nuts] Re: Problem with Solartron 7071 David, The Coto 3400 Series relays were low thermal EMF relays. I've attached a PDF of some pages from old EEM catalogs (the Internet Archive has them for download). Sketchy information at best; I haven't found a catalog of the complete 3400 series relays. Coto still produces low thermal EMF relays in the 3500 & 3600 series. Don't know if either of these would be a good fit for your instrument, or if they're available from any of the usual suppliers. You didn't describe your relay as to form factor, coil & contact arrangements, but there are several Coto 3400 series relays listed on Ebay. With a little Yankee Ingenuity, maybe one of them could be adopted by your insrument. Good luch with your search. David Mason Alabama, USA ----- Original Message ----- From: "David C. Partridge via volt-nuts" <volt-nuts@lists.febo.com> To: "Discussion of precise voltage measurement" <volt-nuts@lists.febo.com> Cc: "David C. Partridge" <david.partridge@perdrix.co.uk> Sent: Friday, October 17, 2025 5:23:01 AM Subject: [volt-nuts] Re: Problem with Solartron 7071 Looks like RL5 in the input attenuator circuit isn't opening fully, so above a certain voltage it lets the voltage on its input through to the input of DC ranging circuit. It is a Coto 3400-0051. I can't find any information about that so don't know a suitable replacement. Does anyone have either a) any of these relays to spare, or b) know of a replacement? Thanks David _______________________________________________ volt-nuts mailing list -- volt-nuts@lists.febo.com -- To unsubscribe send an email to volt-nuts-leave@lists.febo.com To unsubscribe, go to and follow the instructions there.

D

DM

Tue, Oct 21, 2025 5:11 PM

David,
Yeah, I was expecting a hefty price tag on a relay of that variety. Seems that anything that has "Low EMF" in its description is expensive. I'm kinda surprised that a replacement was so readily available. My luck with things of this nature has been nonexistence except in a museum.
Good luck with your repair.
David M

----- Original Message -----
From: "David C. Partridge via volt-nuts" volt-nuts@lists.febo.com
To: "Discussion of precise voltage measurement" volt-nuts@lists.febo.com
Cc: "David C. Partridge" david.partridge@perdrix.co.uk
Sent: Tuesday, October 21, 2025 11:48:58 AM
Subject: [volt-nuts] Re: Problem with Solartron 7071

I've checked and I think that a 3602-05-52 is a good replacement. Not cheap mind you ☹

Coto of course didn't reply to my enquiry ☹

David

-----Original Message-----
From: DM via volt-nuts volt-nuts@lists.febo.com
Sent: 17 October 2025 17:17
To: Discussion of precise voltage measurement volt-nuts@lists.febo.com
Cc: DM dgminala@mediacombb.net
Subject: [volt-nuts] Re: Problem with Solartron 7071

David,
The Coto 3400 Series relays were low thermal EMF relays. I've attached a PDF of some pages from old EEM catalogs (the Internet Archive has them for download). Sketchy information at best; I haven't found a catalog of the complete 3400 series relays. Coto still produces low thermal EMF relays in the 3500 & 3600 series. Don't know if either of these would be a good fit for your instrument, or if they're available from any of the usual suppliers.
You didn't describe your relay as to form factor, coil & contact arrangements, but there are several Coto 3400 series relays listed on Ebay. With a little Yankee Ingenuity, maybe one of them could be adopted by your insrument.
Good luch with your search.
David Mason
Alabama, USA

----- Original Message -----
From: "David C. Partridge via volt-nuts" volt-nuts@lists.febo.com
To: "Discussion of precise voltage measurement" volt-nuts@lists.febo.com
Cc: "David C. Partridge" david.partridge@perdrix.co.uk
Sent: Friday, October 17, 2025 5:23:01 AM
Subject: [volt-nuts] Re: Problem with Solartron 7071

Looks like RL5 in the input attenuator circuit isn't opening fully, so above a certain voltage it lets the voltage on its input through to the input of DC ranging circuit.

It is a Coto 3400-0051. I can't find any information about that so don't know a suitable replacement.

Does anyone have either a) any of these relays to spare, or b) know of a replacement?

Thanks
David

volt-nuts mailing list -- volt-nuts@lists.febo.com -- To unsubscribe send an email to volt-nuts-leave@lists.febo.com To unsubscribe, go to and follow the instructions there.

volt-nuts mailing list -- volt-nuts@lists.febo.com -- To unsubscribe send an email to volt-nuts-leave@lists.febo.com
To unsubscribe, go to and follow the instructions there.

David, Yeah, I was expecting a hefty price tag on a relay of that variety. Seems that anything that has "Low EMF" in its description is expensive. I'm kinda surprised that a replacement was so readily available. My luck with things of this nature has been nonexistence except in a museum. Good luck with your repair. David M ----- Original Message ----- From: "David C. Partridge via volt-nuts" <volt-nuts@lists.febo.com> To: "Discussion of precise voltage measurement" <volt-nuts@lists.febo.com> Cc: "David C. Partridge" <david.partridge@perdrix.co.uk> Sent: Tuesday, October 21, 2025 11:48:58 AM Subject: [volt-nuts] Re: Problem with Solartron 7071 I've checked and I think that a 3602-05-52 is a good replacement. Not cheap mind you ☹ Coto of course didn't reply to my enquiry ☹ David -----Original Message----- From: DM via volt-nuts <volt-nuts@lists.febo.com> Sent: 17 October 2025 17:17 To: Discussion of precise voltage measurement <volt-nuts@lists.febo.com> Cc: DM <dgminala@mediacombb.net> Subject: [volt-nuts] Re: Problem with Solartron 7071 David, The Coto 3400 Series relays were low thermal EMF relays. I've attached a PDF of some pages from old EEM catalogs (the Internet Archive has them for download). Sketchy information at best; I haven't found a catalog of the complete 3400 series relays. Coto still produces low thermal EMF relays in the 3500 & 3600 series. Don't know if either of these would be a good fit for your instrument, or if they're available from any of the usual suppliers. You didn't describe your relay as to form factor, coil & contact arrangements, but there are several Coto 3400 series relays listed on Ebay. With a little Yankee Ingenuity, maybe one of them could be adopted by your insrument. Good luch with your search. David Mason Alabama, USA ----- Original Message ----- From: "David C. Partridge via volt-nuts" <volt-nuts@lists.febo.com> To: "Discussion of precise voltage measurement" <volt-nuts@lists.febo.com> Cc: "David C. Partridge" <david.partridge@perdrix.co.uk> Sent: Friday, October 17, 2025 5:23:01 AM Subject: [volt-nuts] Re: Problem with Solartron 7071 Looks like RL5 in the input attenuator circuit isn't opening fully, so above a certain voltage it lets the voltage on its input through to the input of DC ranging circuit. It is a Coto 3400-0051. I can't find any information about that so don't know a suitable replacement. Does anyone have either a) any of these relays to spare, or b) know of a replacement? Thanks David _______________________________________________ volt-nuts mailing list -- volt-nuts@lists.febo.com -- To unsubscribe send an email to volt-nuts-leave@lists.febo.com To unsubscribe, go to and follow the instructions there. _______________________________________________ volt-nuts mailing list -- volt-nuts@lists.febo.com -- To unsubscribe send an email to volt-nuts-leave@lists.febo.com To unsubscribe, go to and follow the instructions there.

M

mitch@vincentelectronics.com

Wed, Oct 22, 2025 1:59 AM

I've got a pair of 3602-05-72 parts.

Best regards,

mitch

-----Original Message-----
From: David C. Partridge via volt-nuts volt-nuts@lists.febo.com
Sent: Tuesday, October 21, 2025 12:49 PM
To: 'Discussion of precise voltage measurement' volt-nuts@lists.febo.com
Cc: David C. Partridge david.partridge@perdrix.co.uk
Subject: [volt-nuts] Re: Problem with Solartron 7071

I've checked and I think that a 3602-05-52 is a good replacement. Not cheap mind you ☹

Coto of course didn't reply to my enquiry ☹

David

-----Original Message-----
From: DM via volt-nuts volt-nuts@lists.febo.com
Sent: 17 October 2025 17:17
To: Discussion of precise voltage measurement volt-nuts@lists.febo.com
Cc: DM dgminala@mediacombb.net
Subject: [volt-nuts] Re: Problem with Solartron 7071

David,
The Coto 3400 Series relays were low thermal EMF relays. I've attached a PDF of some pages from old EEM catalogs (the Internet Archive has them for download). Sketchy information at best; I haven't found a catalog of the complete 3400 series relays. Coto still produces low thermal EMF relays in the 3500 & 3600 series. Don't know if either of these would be a good fit for your instrument, or if they're available from any of the usual suppliers.
You didn't describe your relay as to form factor, coil & contact arrangements, but there are several Coto 3400 series relays listed on Ebay. With a little Yankee Ingenuity, maybe one of them could be adopted by your insrument.
Good luch with your search.
David Mason
Alabama, USA

----- Original Message -----
From: "David C. Partridge via volt-nuts" volt-nuts@lists.febo.com
To: "Discussion of precise voltage measurement" volt-nuts@lists.febo.com
Cc: "David C. Partridge" david.partridge@perdrix.co.uk
Sent: Friday, October 17, 2025 5:23:01 AM
Subject: [volt-nuts] Re: Problem with Solartron 7071

Looks like RL5 in the input attenuator circuit isn't opening fully, so above a certain voltage it lets the voltage on its input through to the input of DC ranging circuit.

It is a Coto 3400-0051. I can't find any information about that so don't know a suitable replacement.

Does anyone have either a) any of these relays to spare, or b) know of a replacement?

Thanks
David

volt-nuts mailing list -- volt-nuts@lists.febo.com -- To unsubscribe send an email to volt-nuts-leave@lists.febo.com To unsubscribe, go to and follow the instructions there.

I've got a pair of 3602-05-72 parts. Best regards, mitch -----Original Message----- From: David C. Partridge via volt-nuts <volt-nuts@lists.febo.com> Sent: Tuesday, October 21, 2025 12:49 PM To: 'Discussion of precise voltage measurement' <volt-nuts@lists.febo.com> Cc: David C. Partridge <david.partridge@perdrix.co.uk> Subject: [volt-nuts] Re: Problem with Solartron 7071 I've checked and I think that a 3602-05-52 is a good replacement. Not cheap mind you ☹ Coto of course didn't reply to my enquiry ☹ David -----Original Message----- From: DM via volt-nuts <volt-nuts@lists.febo.com> Sent: 17 October 2025 17:17 To: Discussion of precise voltage measurement <volt-nuts@lists.febo.com> Cc: DM <dgminala@mediacombb.net> Subject: [volt-nuts] Re: Problem with Solartron 7071 David, The Coto 3400 Series relays were low thermal EMF relays. I've attached a PDF of some pages from old EEM catalogs (the Internet Archive has them for download). Sketchy information at best; I haven't found a catalog of the complete 3400 series relays. Coto still produces low thermal EMF relays in the 3500 & 3600 series. Don't know if either of these would be a good fit for your instrument, or if they're available from any of the usual suppliers. You didn't describe your relay as to form factor, coil & contact arrangements, but there are several Coto 3400 series relays listed on Ebay. With a little Yankee Ingenuity, maybe one of them could be adopted by your insrument. Good luch with your search. David Mason Alabama, USA ----- Original Message ----- From: "David C. Partridge via volt-nuts" <volt-nuts@lists.febo.com> To: "Discussion of precise voltage measurement" <volt-nuts@lists.febo.com> Cc: "David C. Partridge" <david.partridge@perdrix.co.uk> Sent: Friday, October 17, 2025 5:23:01 AM Subject: [volt-nuts] Re: Problem with Solartron 7071 Looks like RL5 in the input attenuator circuit isn't opening fully, so above a certain voltage it lets the voltage on its input through to the input of DC ranging circuit. It is a Coto 3400-0051. I can't find any information about that so don't know a suitable replacement. Does anyone have either a) any of these relays to spare, or b) know of a replacement? Thanks David _______________________________________________ volt-nuts mailing list -- volt-nuts@lists.febo.com -- To unsubscribe send an email to volt-nuts-leave@lists.febo.com To unsubscribe, go to and follow the instructions there. _______________________________________________ volt-nuts mailing list -- volt-nuts@lists.febo.com -- To unsubscribe send an email to volt-nuts-leave@lists.febo.com To unsubscribe, go to and follow the instructions there.