122 sticks on fast after a while

[Papus]

Recently I installed a new set of 6550's and a 12AU7 (audio position) in my 122-V.
The speed switching 12AU7 seemed to be in good condition, so I did not replace it.

After a period of use, the 122 gets stuck on fast. It can be after 20 minutes or after an entire hour, it varies for unknown reasons.
Same result when swapping the 12AU7's.

Thoughts?

[geoelectro]

Fast is the default speed meaning the relay is not engaging. This could be low DC voltage in the amp, weak relay coil, or bad contacts on the relay. These are the typical problems.

Geo

[Papus]

Fast is the default speed meaning the relay is not engaging. This could be low DC voltage in the amp, weak relay coil, or bad contacts on the relay. These are the typical problems.

Geo

What's the easiest way to obtain slow only, assuming my relay is no longer engaging?
I have a recording session in two days, there's no way the relay will be replaced by then - so I'd prefer slow-only if it comes down to that.
Is it as simple as removing the fast motor plug from the amp chassis? or swapping fast and slow motor plugs?

Note: I'm in 240V land, it's not as simple as bypassing the Leslie altogether and plugging my slow motors straight into a 110V wall outlet

[kziss]

Hi Papus.
Yes you can simply swap the slow and fast motor plugs so that the slow motors will be on by default.

Just be careful to not accidentally plug any of the motors into the 240 volt Reverb amplifier power socket which is right next to the four motor sockets.

The 240 volt Reverb amplifier power socket was originally covered over with a piece of red tape, but the red tape might possibly have come off so therefore it is easy to accidentally insert the motor plug into the 240 volt Reverb amplifier socket which is an identical type socket to that of the four motor sockets.
All the best.
Kon.

[Papus]

Thanks Kon.
This worked, kept the 122 on slow to get me through the recording session.
I took a direct output from my T202 so I can re-amp through the 122 in future when the speed control has been fixed.
The Reverb Amp sticker is intact on my 122 :)

[Papus]

Fast is the default speed meaning the relay is not engaging. This could be low DC voltage in the amp, weak relay coil, or bad contacts on the relay. These are the typical problems.

Geo

Does the 122's behavior where the speed switching works for a while (30-60 minutes, it seems to vary) provide any clues about where the fault lies?
The relay clicks audibly, even after the switching ceases to have any effect on motor speed.

[muckelroy]

Your last question is a bit hard to understand. Are you saying that you switch to slow at the organ, you hear a relay "click" at that moment, but it stays on fast?

If that is what you are saying, it's likely the 0.1uf capacitors across the motor sockets are probably leaky and need replacement.

This set of symptoms would make me more suspicious of a weak / faulty relay if the motors stopped altogether.

[muckelroy]

Thinking out loud here... 122 type Leslie speakers have one of the most complex speed switching systems of any of the Leslie models. There are many variables, and failure points.

But, all it takes is one day to service ALL of the components that play in to the speed switching system. Servicing it piece by piece will not save you from something else failing in the future.

In a situation where speed switching is mission critical (such as a church, or a recording studio, etc), I would recommend the following services:

Leslie amp:
-- Replace the 0.1 uF capacitors across the motor sockets. (These may be of a different value if you are using a 240V Leslie, not sure)
-- Replace the relay, if it is questionable, original, or intermittent
-- Check all wiring around the motors, the 5 pin jumper plug, etc. Re-flow any loose or questionable solder joints.
-- Replace the 470 ohm 1/2 watt, and 10k 7 watt resistor with high quality new resistors, if they are original.
-- Replace the 1 megaohm resistor going from the input to the switching tube, as well as the switching tube if it is weak.
-- Clean switching tube socket and tube pins.
-- Service all motor stacks. (Maybe it is, indeed, switching but "stuck on slow" could be a mis-aligned motor stack in disguise.)

In organ:
-- Check all resistors and capacitors in the Leslie kit, if it is a vintage kit. At minimum, replace the 10uF 450V capacitor. Replace all resistors if you want to go hog wild, paying attention to power ratings throughout.
-- Check all speed switch solder joints, wiring, mounting is secure, replace any parts as necessary.
-- If the Leslie kit uses an organ rectifier socket adapter, consider replacing that with a new 33k resistor on the appropriate rectifier pin for the model organ, and a wire, dressed and running in to the preamp in a secure manner. (These rectifier socket adapters are a common failure point.)

See? There are SO MANY possible failure points, so I thought I'd just list all the things that a tech might check, or if someone was doing a proactive service / rebuild, they would replace these, and more, all for the sake of reliable speed switching.