ampage Tube Amps / Music Electronics	For current discussions, please visit Music Electronics Forum.

ampage archive

Vintage threads from the first ten years

Laney AOR 50W sounds like .50W

:

12/10/2004 1:11 PM

Laney AOR 50W sounds like .50W

Howdy,

I was wondering if anyone else had run into this before. I recently retubed my Laney Protube 50 with 4 fresh 12ax7s (the EL34's were also recent). It sounded great when I played it the first day for about an hour. The next day I fired it up to find:
The volume was so low that I had to have my ear about 3" from the speaker to hear anything.

The preamp tube just before the PI was cracked and blackened. I replaced this one and found no change in the volume.

All other features seem to work fine, no hums, sizzles or buzzes, adjusting pre gain levels affects the distortion, etc.

Voltages measured on tube pins seem to be good, reasonably close to the Laney voltage chart in Tom Mitchell's book.

I have swapped tubes, and all the other usual checks, and can only think this may be an OT problem.

I would appreciate any ideas.

Thanks in advance.

Keith

12/13/2004 4:20 PM

sounds like a PI problem honestly. I'd recheck all voltages there, and check the socket, swap tubes again..

If that turns up nothing, work from the output tube grids back using the circuit disturbance test to see where the signal dies out. Or if you have a signal gen, use that to trace the signal through the amp to the point where things go awry.

Generally, if an OT goes you will have no signal, or major hum. A weak signal with nothing else going on says to me there is a weak signal on the output tube grids.

How is current draw on output tubes? Forget voltages for a min.. maybe bias is really cold?

12/13/2004 4:24 PM
Mark Black	I've had a Laney AOR with similar symptoms before and it turned out to be a bad relay (very small one - I think I found a replacement at Digi-Key). Not the easiest amp to access the solder-side of the PCB as I remember...

12/13/2004 8:46 PM
Chill	If one of the H11F1's blew, that would probably short the signal to ground at either the first gain pot or at the MV's wiper.

12/14/2004 6:05 AM
Keith	Thanks for the input, guys. I'll check these things out. Keith

Page 1 of 1