FIXED my Orange Valve Tester

Keefy

Today I checked out all the valves in my friend’s 2001 Fender Pro Reverb. The amp has 7x 12AX7 valves and a 12AT7. Without exception the tester gave a low score* (5-7) to all the ‘A’ triodes, and a much higher score (10-14) to the ‘B’ triodes. Looking back at my test notes for other valves this happens a lot. All today’s valves were Groove Tubes, mostly re-badged Sovteks.

Can anyone suggest what might be responsible for this bias? (No pun intended.)


*The device gives an arbitrary score of up to 15. It fails any valve which scores 5 or lower, and any dual triode where the scores differ by more than 6 points.

springhead

Does it just look at emission, or does it apply a signal of any kind and check gm?

ICBM

At best it sounds like it's out of calibration.

Keefy

springhead said:

Does it just look at emission, or does it apply a signal of any kind and check gm?

I don’t know, Orange don’t specify.

ICBM said:

At best it sounds like it's out of calibration.

Oh flip. I’ll drop Orange an email and see what they say. That thing wasn’t cheap.

Keefy

I've messaged Orange via their contact page. There is a 'CALIB. OK' sticker on the base of the unit, so clearly that is a thing.

Caffeine_Vampire

You're welcome to try my tester if you're in the neighbourhood. 

Keefy

Caffeine_Vampire said:

You're welcome to try my tester if you're in the neighbourhood. 

Thanks but Cheshire is a bit outside my bailiwick!

I’ll see what Orange say to start with. I also have a DIY tester build on the back burner, subject to finding the right mains transformer.

Keefy

This doesn’t look promising - initial calibration only: https://www.thegearpage.net/board/index.php?threads/orange-vt1000-tube-tester-some-questions-answered.1390885/

Keefy

...but this is interesting: http://www.ampworks.co.uk/recent-repairs/orange-vt1000-valve-tester-repair/

I removed and re-applied the solder to pins 6 and 7 of the preamp valve socket, which possibly looked to be cracked, but no change.

Keefy

Still nothing from Orange. I’m going to clean out the valve sockets, re-flow all their solder joints, and see what happens.

And probably buy a restored old valve tester.

Keefy

Today I cleaned the noval sockets by rotating a cocktail stick dipped in isopropanol. Then I took the unit apart and had another look at the valve socket PCB. I checked the 1k surface mount resistors and found that the one connecting to pin 7 (one of the grids) was showing open circuit between the socket and the ribbon connector. The resistor itself tested at close to 1k but if you look at the picture below you can see there is very little solder at the end of R6 by the tip of the cocktail stick. 

I soldered the end of R6, put it all back together, and tried some pre-amp valves where I had previously marked their scores on the boxes - all now gave more closely matched results, without the big difference previously noted.

FIXED!

Looking at my old valve test records (yes I should get out more!) I saw that my early results didn't show that consistent offset, so I think what solder there was must have let go at some point while I've owned the unit. Would Orange care if I told them about this? Probably not.

I might still get one of those old testers with all the knobs and levers though, just for shits and giggles.

ICBM

Yes, that's a faulty joint - you can see the solder hasn't wetted onto the resistor. As you say, it very likely worked like that for some time with just the metal making physical contact - so would also have passed the factory test - but eventually some oxidation/corrosion got in and it failed.

The pin 6 and possibly pin 7 joints of the same valve socket also look dodgy, if you haven't already spotted that. 

Keefy

ICBM said:

Yes, that's a faulty joint - you can see the solder hasn't wetted onto the resistor. As you say, it very likely worked like that for some time with just the metal making physical contact - so would also have passed the factory test - but eventually some oxidation/corrosion got in and it failed.

The pin 6 and possibly pin 7 joints of the same valve socket also look dodgy, if you haven't already spotted that. 

Yes I had already re-soldered 6 and 7. At least I’ve upgraded them from ‘cracked’ to ‘dodgy’!

EDIT: Yes they look really crap in that photo but in real life they are fine!

digitalkettle

Nice work!

Keefy

digitalkettle said:

Nice work!

Cheers!

I went back to my re-done solder joints, removed the solder again, and smeared a little flux along the tabs before redoing them. Now I have visibly continuous solder. I am happy and so should ICBM be!

BillDL

Keefy said:

....... Would Orange care if I told them about this? Probably not.

They probably will when you send them an invoice for several hours of your time taken up diagnosing and fixing the problem.

Keefy

BillDL said:

Keefy said:

....... Would Orange care if I told them about this? Probably not.

They probably will when you send them an invoice for several hours of your time taken up diagnosing and fixing the problem.

I’m more concerned about the cost of all those valves that I chucked because I thought they were u/s!




Actually I kept them because, well, you never know…

Dave_Mc

Great news, nice work!