Distortion from Leslie 122 Amplifier

[musika]

I have been trying to track down a scratchy low level crackling distortion problem in my Hammond CV /  Leslie 122.  Visual inspection revealed a cracked 10K 7 Watt resistor which I marked in the schematics.  I pulled it out and it tested at about 250K instead of 10K.  I haven't replaced it yet since I am waiting for the part, but I am wondering what other damage this may have caused in the amplifier (if any),  assuming this is the cause of the distortion. 

 

[musika]

The 10K resistor.

 

[musika]

The Leslie 122 amplifier.

 

[Tubetec]

The 10k resistor has no effect at all on whats going on in the 122 , it will have an effect on the voltage at the socket marked 'to console' . Its definately not the cause of your problem .

 

[musika]

That would be pin 5 (B+ supply to the connector kit and/or preamp) on the 6 pin connector.  The scratchy distortion always appears after the amp has been on for 3-5 minutes.

 

[JohnRoberts]

if the resistor is bad, replace it...  Then check again.

JR

 

[musika]

Thanks... that's my plan for now.  Once I pulled the resistor, it literally fell apart.

 

[JBorum]

I sometimes get some nasty crackles in my Hammond/122 from seemingly insignificant movement of the cable which connects them. As in, a nearby footstep by that doesn't visually move the cable in the least. I'm sure it's the cable because I can recreate the noise at will. I'm sure it only needs some solder joints refreshed, but I haven't gotten around to it yet.

I'm sure that's too painfully obvious and not your problem, but it's worth a shot.

 

[musika]

Thanks for your post.  I replaced the female end of the 6 pin Hammond / Leslie cable with a new connector a few weeks ago with a new one from TWG.  The old one was one of those pre-molded connectors and when moving it slightly, it would create that loud crackling noise you refer to.  That was a big improvement, but was not the cause of my distortion.  If you have what you think may be cable / connector issues, re-flowing the solder connections on the connector or replacing it may help a lot.  As for this distortion issue,  the CV preamp has been pulled out and serviced with new preamp tubes.  Also, last week replaced the Leslie 122 amp tubes one at a time to try to isolate this problem to no avail. 

 

[fazer]

Is this noise ghosting a signal from the organ/guitar or just on its own under no signal condition?

If it’s under no signal,  use freeze mist on parts.  And see if it goes away.

If under signal from organ.

Tube sockets maybe need Clean with cleaner and small brush’s from a gun shop.  They are small enough to get into pin slots.  This Can also be from coupling caps between tube stages.  Bad  Carbon comp Resistors heating up can cause this.  Also  electrolytic powers caps can have problems as the age.    Also solder joints on terminal strips.    An Oscope would let you observe the stage it’s happening in and find a location in the tube stage.

If it happens when the signal is from the organ, This kind of problem can also be caused by the screen voltage being equal or above the plate voltage on the output tubes.

 

[pucho812]

Does the distortion happen with the organ expression pedal at minimum? does it happen at any adjusted volume level  on the 122?

 

[musika]

This is a low level static crackling noise that is present with the organ expression pedal level at minimum - it takes 4-5 minutes to appear from a cold start - before that everything is great.. I have the amp on my bench right now, but from what I remember, it is also not affected by an increase of the volume pot on the 122 amp.  But I would need to check that..

 

[musika]

Also solder joints on terminal strips. 

... I will touch up these, just to make sure.

Tube sockets maybe need Clean with cleaner and small brush’s from a gun shop.

... do these need to be brass bristle brushes?  I have been using the small dental floss nylon brushes with DeOxit on the tube sockets.

 

[Michael Tibes]

I'd replace the caps and give the whole unit a very thorough cleaning. If it's still happening I'd visually inspect the soldering and fix it if necessary and also  look into the resistors. Apart from replacing them all it might need a methodical approch to find a bad one though. Changing the tubes just to be sure might help too, just to rule them out...

Michael

 

[musika]

if the resistor is bad, replace it...  Then check again.

...replaced the 10K 10W resistor and all is good.  Leslie sounds great again.  Thanks for all the replies!