SECO GCT-9 Grid Circuit Tester - UK Vintage Radio Repair and Restoration Discussion Forum

tri-comp · 11th Jul 2018, 7:50 pm

I recently came into possesion of a SECO GCT-9 Valve-tester or rather a Grid Circuit Tester.
This is a special instrument that will show if a valve is suffering from Control-grid current among other things.
Especially output valves, here 6973, but also valves like ECL86 and probably some U-series output valves as well are prone to developing grid-current.
Possibly because of the infamous "That Capacitor"-syndrome or whatever.
The bottom line is that will you Valve-tester capture these valves during a quick test ?
The SECO GCT-9 will !
Here's a few pictures the last one showing a 6973 with excessive G-1 current.
The 2nd to last is showing an ECC83 on a slippery slope, in the process of developing G-1 current.
The 3rd. Eye-picture shows no G-1 current, as no valve to test has been inserted. This is the normal display with a healthy valve.

I'm including a scan of the setup-manual that should also be good for earlier versions in the GCT-series.
I believe the GCT-9 was the last SECO made.
The manual is in a low 72-dpi resolution and if someone wants a better quality (600-dpi) just send a PM with your e-mail address.

tri-comp · 11th Jul 2018, 7:51 pm

Continuation...

Info: Eye is a 6AF6 and the double-triode a 12AU7

FrankB · 16th Jul 2018, 9:58 am

I have a couple of those units stashed away.
They work well and IIRC, basically they use the same GCT circuit that my Seco 107C uses. Extremely sensitive too. Solved a lot of "tough dog" tuner problems with them years back.
Minimal demand for them here in my area. Typically sell for 5-10.00 USD at the ham fairs, or sometimes in the "free" boxes. If nothing else a great source for tube sockets. Mostly they were used very little in the majority of shops here. You can tell how much use they had by the brightness of the eye tube, and the condition of the sockets.

tri-comp · 16th Jul 2018, 5:12 pm

Mine has certainly seen minimal use; the eye near mint as I can judge it.
Sockets are good with a firm grip.
I had to pay $25/ and found it to be a bargain.
If some are out there for a tenner, go get'em !
Who would ever cannibalize a test set like this for valve-sockets ?
Possibly people don't know exactly what it does ?
For sorting out valves with grid-current they're the best and valves do run into grid-current not only in tuners.
I have seen several ECL86/6GW8 valves with that exact problem lately.
Hard to spot on an emission tester even if some claim to be good at it (Could be B&K's 606, 607, 677 etc.)
The valve runs normal with rated plate-current/cathode-voltage for a while in the set when warming and then the current will suddenly rise ~50% after a couple of minutes.
The SECO will pick-out the trouble maker easily if grid-current is the issue.

Ed_Dinning · 16th Jul 2018, 8:44 pm

Hi, it looks as if that circuit could easily be adapted for the Sussex valve tester.
Help find all those faulty UL41's..

Ed

11th Jul 2018, 7:50 pm	#1
tri-comp Heptode Join Date: Oct 2008 Location: Aalborg, Denmark Posts: 903	SECO GCT-9 Grid Circuit Tester I recently came into possesion of a SECO GCT-9 Valve-tester or rather a Grid Circuit Tester. This is a special instrument that will show if a valve is suffering from Control-grid current among other things. Especially output valves, here 6973, but also valves like ECL86 and probably some U-series output valves as well are prone to developing grid-current. Possibly because of the infamous "That Capacitor"-syndrome or whatever. The bottom line is that will you Valve-tester capture these valves during a quick test ? The SECO GCT-9 will ! Here's a few pictures the last one showing a 6973 with excessive G-1 current. The 2nd to last is showing an ECC83 on a slippery slope, in the process of developing G-1 current. The 3rd. Eye-picture shows no G-1 current, as no valve to test has been inserted. This is the normal display with a healthy valve. I'm including a scan of the setup-manual that should also be good for earlier versions in the GCT-series. I believe the GCT-9 was the last SECO made. The manual is in a low 72-dpi resolution and if someone wants a better quality (600-dpi) just send a PM with your e-mail address. Attached Thumbnails

16th Jul 2018, 9:58 am	#3
FrankB Heptode Join Date: Oct 2005 Location: Olympia, Washington, USA. Posts: 664	Re: SECO GCT-9 Grid Circuit Tester I have a couple of those units stashed away. They work well and IIRC, basically they use the same GCT circuit that my Seco 107C uses. Extremely sensitive too. Solved a lot of "tough dog" tuner problems with them years back. Minimal demand for them here in my area. Typically sell for 5-10.00 USD at the ham fairs, or sometimes in the "free" boxes. If nothing else a great source for tube sockets. Mostly they were used very little in the majority of shops here. You can tell how much use they had by the brightness of the eye tube, and the condition of the sockets.

16th Jul 2018, 5:12 pm	#4
tri-comp Heptode Join Date: Oct 2008 Location: Aalborg, Denmark Posts: 903	Re: SECO GCT-9 Grid Circuit Tester Mine has certainly seen minimal use; the eye near mint as I can judge it. Sockets are good with a firm grip. I had to pay $25/ and found it to be a bargain. If some are out there for a tenner, go get'em ! Who would ever cannibalize a test set like this for valve-sockets ? Possibly people don't know exactly what it does ? For sorting out valves with grid-current they're the best and valves do run into grid-current not only in tuners. I have seen several ECL86/6GW8 valves with that exact problem lately. Hard to spot on an emission tester even if some claim to be good at it (Could be B&K's 606, 607, 677 etc.) The valve runs normal with rated plate-current/cathode-voltage for a while in the set when warming and then the current will suddenly rise ~50% after a couple of minutes. The SECO will pick-out the trouble maker easily if grid-current is the issue.

16th Jul 2018, 8:44 pm	#5
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: SECO GCT-9 Grid Circuit Tester Hi, it looks as if that circuit could easily be adapted for the Sussex valve tester. Help find all those faulty UL41's.. Ed