Leslie 225 Cab needs help...HELP!

[fluhome]

I recently aquired a Leslie 225 cab and it has been put into use for about 5 hours over the term of a couple weeks. It sounded better than great until the sound quality degraded and a industrial burning smell ran us out of the room.
It has an internal tube amp with 2-6L6's and a 12AU7 preamp tube. The O/P tubes tested OK but the 12AU7 was bad. I replaced all tubes and problem still exists. Capacitors???? Any help would be appreciated.
Terry

[PRNDL]

Something else is wrong.

The two places to look are the output tubes and electrolytic capacitors. (How did you test the output tubes?)

Begin with a visual inspection and see if you can spot a burnt resistor.

Next measure all the resistors, beginning with those connected to the 12AU7. Values within the circuit will be lower than normal, but a bad one will be way off. Unsolder it and measure it. Replace any that are more than 10-20% off.

Remove the tubes and turn the amp on. Check all voltages on the tubes and in the power supply.

If everything is normal, put the tubes back in, turn on the amp and check the bias.

[amptech]

Burning smell not good at all! dont replace any more valves untill you or someone checks the unit first,if possilbe try to get the circuit diagram that way you can see whats going on. dischage the psu before inspection that way your be safe!
cheers 4 now,
amptech

[Steve S]

Link to 125/225 schematic: http://captain-foldback.com/Leslie_s...matics/125.GIF

There is a clearer picture of this on p.7 of the manual. For this go to captain-foldback.com, click on Leslie at the bottom of the page, then click on "Download Leslie Manuals", then scroll down to the 125/225 manual icon.

The schematic calls for 6L6GC tubes, which have significantly higher plate and screen ratings than the plain 6L6s or the G/GA/GB versions. You might have a problem if you are not using the GC version.

This could be as old as 45 or so years, so many of the components like caps probably have drifted from their nominal values.

Are you connecting this to an organ or to something else using an outboard preamp like the Leslie combo preamp?

Steve