Dave the Quad phoned...
"Got an Audio Innovations here, it's cracking in one channel. Can you take a look?"
Yeah .... why not?
It's a Series 300 amplifier from the late 80's early 90's. Not sure I care for it's styling to be honest ... anyway...
The third ECL86's tube base is flashing over... This can be indicative of output transformer failure, a failure in the valve itself, or the amplifier having been run with the speakers disconnected. Once a tube base has started to flash over, no amount of cleaning will sort it reliably. We'll change all four to be on the safe side. Let's hope the transformer is OK. Try as I might to get a photo of it... I couldn't.
Disassembly is a bit of a pain ...
Remove the knobs. They're secured to the shafts of the controls by a small grub screw with a hex head.
Unsolder the wiring to the gain control. A red, white and black wire. I wonder why this network is suspended like this? Added after to remove a bit of DC from the pot perhaps?
There are three M3 nuts, and a few plastic stand offs which must be released to allow access to the print side of the PCB. I removed the valves. Keep the ECL86's in the same order that they were removed.
I gave the PCB a blanket re-solder as a good few of the joints looked suspect, and replaced the four output valve holders.
A lovely sounding amp, and absolutely silent.. no hum and almost no blow. Superb.
It's soak tested with Matt Berry - The Blue Elephant.
Another saved from landfill!
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