Amp repair help needed.

[contaxchen]

Hi I need some help with my EAR amp repair.
I got one channel 's sound much relatively smaller than the other. I swithed both channel's all of tubes. The problem is still there... I measured all of working voltage, cathode, grid, and anode,etc... They are fine according to the schematics. This doesn't solve the problem.
Again, I checked out the coupling capacitors and feedback bypass caps. They are fine.
Everything is OK.
The problematic channel got some kind of hissing sound when I play the music loud. That means the problem is related to the broken components? This unknown component is not stable when strong electric current passes through it. Which one it could be?
Any idea?
Lhchen

[SHiFTY]

Firstly I am guessing you have tried different sources/ preamps and interconnect and speaker cables and eliminated them as a possibility?

With the amp turned off and the caps discharged, check your solder joints, by moving the component legs around. Sounds like you may have a dodgy solder joint somwhere.

Apart from that check the resistors haven't drifted in value, and check the output transformers measure the same.

[richwalters]

Have a peep at the NFB components from sec o/p tranny to input tube. If a feedback cap is duff on this side then the HF phase response will be wild and might aggravate oscillation at certain levels. Or it may be oscillating ultrasonically without knowing about it.

Measuring Ik on each o/p tube (quies) might show minor variations but if amp is AB then it will get worse when heavy output stage currents flow. Without a scope it's awkward; a DVM may display unsteady readings.

Many tube amps aren't keen on LS cross-over networks....perhaps this is a component area to poke about with.
Have you tried swapping speakers ?

richj