JJ value Pair ECC83S

I switched on my amp which had been working perfectly the day before. When I used the footswitch to turn on the spring line reverb, strange sounds came from the amp.  It was the sound of rumbling thunder with reverb. Not good !

So your first thought is the reverb unit is faulty.  Unlikely. My thoughts tuned to the schematic and decided that the ECC83 ( 12AX7) driving the reverb could have become noisy.  I pulled out the possible offending ECC83 and plugged into my Orange tester as a quick test to see if the fault was found the tester came up with the green light for OK.

I was puzzled, so I next tested the valve on my Avo valve characterisation tester and I saw the meter flickering when measuring the current on the second anode.  This was the source of the noise.

I only use Orange tester for quick tests and learned that this tester is not good at testing noisy valves. Note that the valve had not gone microphonic. The noise from the valve was passing through the reverb and creating the weird thundering sound.  I replaced the ECC83 and all was perfect again. A lovely sweet quiet reverb again.

So, don’t jump to the conclusion that the reverb unit itself is faulty till you can either test  the valve or just replace the valve before and after the reverb unit.

The valves in this amp were about 2 years old so it can be expected that the valves will start to fail or sound poor.

We have all the right valves for your amp in our shop 🙂



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