I don’t get many ENGL amp repair, so I was a bit annoyed with myself for not photographing this one. I’m grateful to the owner for helping me out by sending me a photo.
Here were the symptoms, in the words of the customer:
- Overly noisy (hissing / popping) on both clean and overdrive channels at all times (with guitar plugged in or not)
- A couple of noisy (scratchy) pots e.g. Clean and Lead Volumes
- Loss of top end frequencies
- Clean channel intermittent partial volume reduction coupled with distortion.
The first three symptoms were caused by the 12AX7 (ECC83) valves in positions 1 and 2, which were leaking DC onto the valve grid. This was also causing the scratchy pots.
The fourth symptom didn’t show up obviously during bench tests until I checked the output power. The amp delivered just under 50W into 16 ohms via the 16 ohm transformer tap, but only about 10W into 8 ohms using the 8 ohm tap.
I ordered a new output transformer from ENGL. I fitted it the day that it arrived and this fixed the problem completely. The amp was then soak tested for 90 minutes at gigging power levels.
After some discussion with the customer upon collection, it transpired that he was running two eight ohm cabs in parallel into the 8 ohm speaker tap. This would cause a higher current in the transformer secondary, which may have caused the failure. The correct way to run two eight ohm cabs with this amp is to connect them into the series sockets on the 16 ohm tap.
If you’re in need of an ENGL amp repair, please contact me