UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Test Gear and Workshop Equipment

Notices

Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders.

Reply
 
Thread Tools
Old 24th Apr 2024, 10:34 am   #1
Ian - G4JQT
Octode
 
Ian - G4JQT's Avatar
 
Join Date: Jun 2004
Location: Reading/Fakenham, UK.
Posts: 1,333
Default 812A triode on CT160 tester

I know a local watch and clock repairer who has a L&R Vira-Matic ultrasonic cleaner which uses an 812A triode valve. The machine is playing up and the first thing to check is this valve.

I don't have my CT160 or the valve-settings book to hand, but can anyone tell me if the CT160 is able to test this valve before he gives it to me?

Thank you.
Ian - G4JQT is offline   Reply With Quote
Old 24th Apr 2024, 12:40 pm   #2
Chrispy57
Hexode
 
Join Date: Mar 2020
Location: Rochdale, Greater Manchester, UK.
Posts: 496
Default Re: 812A triode on CT160 tester

Hi Ian - the 812A is not listed in the AVO data book (23rd Edition) so it looks like a "no". The CV equivalent of the 812 CV2661 is also absent.

Cheers
Chris

Last edited by Chrispy57; 24th Apr 2024 at 12:51 pm.
Chrispy57 is offline   Reply With Quote
Old 24th Apr 2024, 12:42 pm   #3
Ian - G4JQT
Octode
 
Ian - G4JQT's Avatar
 
Join Date: Jun 2004
Location: Reading/Fakenham, UK.
Posts: 1,333
Default Re: 812A triode on CT160 tester

Thanks Chris. Looks like that saves me a job!
Ian - G4JQT is offline   Reply With Quote
Old 24th Apr 2024, 1:01 pm   #4
Craig Sawyers
Dekatron
 
Craig Sawyers's Avatar
 
Join Date: Nov 2010
Location: Oxford, UK.
Posts: 5,061
Default Re: 812A triode on CT160 tester

Looking at the characteristics, it is a bit of a beast. Operating with grid either positive or negative, and a VAmax of 1500V and substantial current, the AVO valve testers can only access a small corner of the characteristics.

http://www.r-type.org/pdfs/812a.pdf

Which is why I guess it is not in the AVO data books.

Craig
__________________
Doomed for a certain term to walk the night
Craig Sawyers is offline   Reply With Quote
Old 24th Apr 2024, 1:52 pm   #5
Cruisin Marine
Octode
 
Join Date: Jul 2018
Location: Worthing, West Sussex, UK.
Posts: 1,023
Default Re: 812A triode on CT160 tester

Data here
http://www.r-type.org/exhib/aaa0548.htm

Mote that it takes 4 amps heater current, so likely to damage your valve tester.
__________________
"Behind every crowd, there's a silver Moonshine"
Cruisin Marine is offline   Reply With Quote
Old 24th Apr 2024, 8:33 pm   #6
Alan Bain
Pentode
 
Join Date: Jan 2012
Location: Heswall, Merseyside, UK
Posts: 192
Default Re: 812A triode on CT160 tester

The circuit is I think the one attached. Tapped inductor oscillator, but quite a beast 1.4kV HT.
Attached Thumbnails
Click image for larger version

Name:	LR Ultrasonic Driver Circuit Old.jpg
Views:	98
Size:	52.2 KB
ID:	296823  
Alan Bain is offline   Reply With Quote
Old 28th Apr 2024, 8:53 am   #7
Sean Williams
Dekatron
 
Sean Williams's Avatar
 
Join Date: Feb 2005
Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW
Posts: 3,524
Default Re: 812A triode on CT160 tester

From memory, John at Colomor used to test transmitting type valves on the VCM163 with an external heater transformer.

You wont get any meaningful readings, but the 811 triode is similar in specification.

812a arent exactly audiophool territory, so check by substitution isnt going to be an expensive option
__________________
Engineers make things work and have spare bits when finished
Sean Williams is offline   Reply With Quote
Old 28th Apr 2024, 10:56 am   #8
David Simpson
Nonode
 
Join Date: Mar 2008
Location: Aberdeen, UK.
Posts: 2,871
Default Re: 812A triode on CT160 tester

Ian, simple answer is definitely NO. The filament current at 4A is twice what a CT160 could handle. CT160's, with their single all purpose mains transformer, already struggle at 2A. Likewise, MK3's, MK4's, & 163's, even with separate T/F's.
You would need a 12V car battery, with a hefty dropper, to supply 6.3V at 4A, or a big thumper of a DC LV PSU. Even then, to get the high slope triode to work on even the bottom end of the Ia/Vg Curve, AVO VCM's would need to work at max Va & Vg. Also, CT160's have a propensity to jump into PO mode.
Only choice - build a temp DC testing rig, utilising a UX4 valve holder.
I've done this with STC4212D's & their kin. If you have a shot at it - be extremely careful.

Regards, David
David Simpson is offline   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 4:56 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.