Fuck my luck.- first of all the laser has gone tits up on my CD player and now my amp has lost one of it’s right channel.
I was just settling down to listen to some new albums this afternoon and all of sudden the right channel on my Icon audio amp disappears.
I swapped over the speaker cable with the same result, checked the bias on the four EL-34’s and they all show as normal on the vu meter. Switched it off and made sure all the valves are seated properly and fired it up again but it’s still the same.
I’ve also check the TT and CD into my head amp just to rule them out and they’re both fine.
Any else I need to try before taking hammer to it ?
Is the speaker absolutely silent or, if you put your ear up against it, can you hear even a faint hum indicating that it’s on ? Can you hear any sort of a click if you select a different input (might need someone to help you with this) - you probably won’t hear anything unless the volume is set above zero ? In each case comparison with the working channel would be instructive.
Faint hum, assuming it’s equally loud in both channels, says speakers, speaker cables, output stage (EL34s) are all probably OK. If there is an ‘output muting’ circuit then the problem is not that that’s stuck on either.
If, when you’re playing music, there is a faint and perhaps distorted version audible in the poorly channel (you’ll need to unplug the good channel’s input to allow you to hear what’s happening) then that might narrow the possible causes down. It would be interesting to know if the volume control affects it. If there’s just silence apart from the hum then, apart from swapping the valves, there may not be much more you can do without taking the baseplate off.
Can you see that all the small valves’ heaters are glowing (each of the two triodes inside the valve should have its own heater) ? Sometimes it’s hard to see because of the silvery getter flash on the inside of the glass.
The top pic is one of the two 6SN7 valves and the bottom is the single 6SL7 valve.
I assume both valves should have the two glowing filament thingies (technical term there) at the top - the 6SL7 appears to only have one and there does appear to be some soot on the inside of the glass - so a failed valve ?
That would explain it. The 6SL7 is ‘shared’ between the two channels. One of its triodes is used in the L channel and the other one in the R. It looks as though the R one has lost its heater. In the 6xxx valves these are wired in parallel inside the valve itself, so it isn’t a supply problem. I’m afraid you need a new 6SL7.
