Dynaco MKIII hum at speaker without input.

Huh, I checked it and there is 5v (5.21 v actually) ac at the rectifier. I had been checking for DC.
 
Huh, I checked it and there is 5v (5.21 v actually) ac at the rectifier. I had been checking for DC.
That's a good sign. :) Means your power transformer isn't blown, which is a Good Thing.™ Next up, check pins 2 and 8 of the rectifier tube itself (after removing it from the socket, of course!) for continuity. If it checks out, time to check the wiring going to its socket. While you're at it, check for AC voltage at pins 2 and 7 of the dark 6550's socket. If you get 6.3V or thereabouts, check those pins of the 6550 for continuity. Again, good luck!
-Adam
 
OMG, I am the stupidest person in the world. I had accidentally swapped a rectifier and a output tube. Flipped them and all is good. Hum sound that started this whole thing is gone.

When doing the soldiering I was so careful to get the wires back in the right place, checking and rechecking my job against the photos I'd taken. I came in the house and popped the tubes in the wrong sockets and whammo. Nothing.

Alls well that ends well!

>>Thank you so much for your help. I apologise for my dumbness<<<
 
Well done! :) I think that's happened to just about everyone at least once. Consider yourself lucky that the MkIII design is well-thought-out; tube swaps of that sort can, in some cases, be rather expensive. :eek: Sparks, smoke, etc. Still, gotta love the simple fixes. :D
-Adam
 
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