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.
Comments
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
Oh flip. I’ll drop Orange an email and see what they say. That thing wasn’t cheap.
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.
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.
And probably buy a restored old valve tester.
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.
The pin 6 and possibly pin 7 joints of the same valve socket also look dodgy, if you haven't already spotted that.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
EDIT: Yes they look really crap in that photo but in real life they are fine!
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!
Actually I kept them because, well, you never know…