Comark FET Tester type 185 - circuit and manual sought - UK Vintage Radio Repair and Restoration Discussion Forum

Phil G4SPZ · 8th Feb 2016, 12:19 am

I bought this neat little unit for a fiver at the last NVCF, and it has just come to the top of the test gear to-do pile. Yes, I have multiple to-do piles...

The two immediate problems are (a) it takes three obsolete PP4 batteries, and (b) there are also three obsolete Mallory TR-115R 6.75 volt mercury batteries inside, two of which are badly corroded.

Does anyone have a copy of the manual or circuit diagram, please? I can usually sort out alternative battery supplies, but without a circuit I'm a bit in the dark. An internet search has produced nothing helpful. It seems to date from around 1968, if the attached review from the July edition of Wireless World is anything to go by.

Thank you,

Phil

Brian R Pateman · 8th Feb 2016, 1:29 pm

Good grief Phil, you do come up with some obscure kit!

Comark was a very good maker of test equipment, and I used to have quite a bit to do with their stuff but I've not encountered this one before.

It's unlikely that I have any thing on it in my "loft archive" but I'll drop an e-mail to an old colleague of mine to see what he might have lurking about somewhere (he used to work for Comark).

Phil G4SPZ · 8th Feb 2016, 2:16 pm

Thank you, Brian, that's much appreciated. As for the obscure kit, well yes, but it tends to find me rather than the other way round... and no matter how obscure, somehow a Forum member somewhere usually knows something about it!

For what it's worth, I did e-mail Comark (now part of the Fluke empire) but as in so many similar cases they have no records remaining on any of the original company's products. The meter is indeed beautifully constructed, so if I can arrange suitable power supplies I'm reasonably confident that it will work.

Phil G4SPZ · 9th Feb 2016, 1:30 am

Quick update - I've now got this tester working, using three PP3 batteries for the Vds supply and two PP3s for the Vgs supply. After cleaning a few switches, it gave realistic readings in line with the data sheet when testing a 2N3819. I also checked the calibration of the two voltage controls and they are both spot-on! I now need to complete the mods to the battery supply.

I'm guessing at the method of operation though, so any info such as a user manual would still be appreciated.

Phil

8th Feb 2016, 12:19 am	#1
Phil G4SPZ Dekatron Join Date: Apr 2005 Location: Bewdley, Worcestershire, UK. Posts: 4,748	Comark FET Tester type 185 - circuit and manual sought I bought this neat little unit for a fiver at the last NVCF, and it has just come to the top of the test gear to-do pile. Yes, I have multiple to-do piles... The two immediate problems are (a) it takes three obsolete PP4 batteries, and (b) there are also three obsolete Mallory TR-115R 6.75 volt mercury batteries inside, two of which are badly corroded. Does anyone have a copy of the manual or circuit diagram, please? I can usually sort out alternative battery supplies, but without a circuit I'm a bit in the dark. An internet search has produced nothing helpful. It seems to date from around 1968, if the attached review from the July edition of Wireless World is anything to go by. Thank you, Phil Attached Thumbnails __________________ Phil Optimist [n]: One who is not in possession of the full facts Last edited by Phil G4SPZ; 8th Feb 2016 at 12:37 am. Reason: Further ID info added

8th Feb 2016, 1:29 pm	#2
Brian R Pateman Nonode Join Date: Jun 2005 Location: Western Lake District, Cumbria (CA20) - UK Posts: 2,136	Re: Comark FET Tester type 185 - circuit and manual sought Good grief Phil, you do come up with some obscure kit! Comark was a very good maker of test equipment, and I used to have quite a bit to do with their stuff but I've not encountered this one before. It's unlikely that I have any thing on it in my "loft archive" but I'll drop an e-mail to an old colleague of mine to see what he might have lurking about somewhere (he used to work for Comark). __________________ Brian

8th Feb 2016, 2:16 pm	#3
Phil G4SPZ Dekatron Join Date: Apr 2005 Location: Bewdley, Worcestershire, UK. Posts: 4,748	Re: Comark FET Tester type 185 - circuit and manual sought Thank you, Brian, that's much appreciated. As for the obscure kit, well yes, but it tends to find me rather than the other way round... and no matter how obscure, somehow a Forum member somewhere usually knows something about it! For what it's worth, I did e-mail Comark (now part of the Fluke empire) but as in so many similar cases they have no records remaining on any of the original company's products. The meter is indeed beautifully constructed, so if I can arrange suitable power supplies I'm reasonably confident that it will work. __________________ Phil Optimist [n]: One who is not in possession of the full facts Last edited by Phil G4SPZ; 8th Feb 2016 at 2:17 pm. Reason: Clarity

9th Feb 2016, 1:30 am	#4
Phil G4SPZ Dekatron Join Date: Apr 2005 Location: Bewdley, Worcestershire, UK. Posts: 4,748	Re: Comark FET Tester type 185 - circuit and manual sought Quick update - I've now got this tester working, using three PP3 batteries for the Vds supply and two PP3s for the Vgs supply. After cleaning a few switches, it gave realistic readings in line with the data sheet when testing a 2N3819. I also checked the calibration of the two voltage controls and they are both spot-on! I now need to complete the mods to the battery supply. I'm guessing at the method of operation though, so any info such as a user manual would still be appreciated. Phil Attached Thumbnails __________________ Phil Optimist [n]: One who is not in possession of the full facts