Leslie 147 Hum only at slow speed, Help!

[okdk]

Hi all, I've played organ all my life and finally just bought myself my first Hammond, a C3 with a 147 leslie. What a dream come true!!! I know I'll be good at fixing things some day but for now I'm kind of green. I've read a lot about hum with 147's but this one makes a loud low hum only in slow speed, when I switch to fast it's completely gone. If I turn the amp down to about 5 it's not audible, but it gets really loud around 8 and even louder at 10, but in fast speed it's fine. I opened up the half moon switch to see if anything looked suspicious but didn't see anything. I've read about changing out the caps and resistors, but it only is bad in slow. Can anybody give me some good advise where to start? Thanks

[TheAdmiral]

Welcome and congratulations on the acquisitions.</p>

I'd first check the cap on the slow plug in the 147 amp to see if it's open. Depending on the age of the amp it could be either black, green or orange.</p>

[tonedeaf]

Is your 147, not the amp but the cabinet a real 147 or a 47 with two speed motors added? If the lower motor is hanging down by the amplifier it will induce AC hum from the motor winding into the 12ax7[?] and cause hum when on slow speed. This is of course if the motor was installed that way instead of up on the base speaker shelf as it would be on a real 145/147. If it is a 147 forget my ramble and check what others post. Frank

[okdk]

I'm sorry, but I'm not sure what you mean. Could you be more specific, like I said, I'm a little green.</p>

By the way, after playing for a while this evening I think the hum goes away when I play full chords on the manuals. When I stop I hear it come back quickly. ??</p>

[okdk]

It's a real 147

[okdk]

Welcome and congratulations on the acquisitions.</p>

I'd first check the cap on the slow plug in the 147 amp to see if it's open. Depending on the age of the amp it could be either black, green or orange.</p>

</p>

</p>

I'll have to bring my meter home tomorrow from work, I think I know what you want me to do. Thanks, will let you know tomorrow.</p>

[okdk]

I spent some time looking at the amp, then plugged the leslie cable back in and turned on the organ; no hum!! However there was no sound as well, or some broken up sound. I didn't have the plug in all the way flush, it was just a hair out. So I pushed it in flush and the hum comes back, with the organ sound. Maybe it's a bad connector or cable end and just not making good contact relating to slow speed?

[geoelectro]

Is the Leslie located on the bass end of the organ? You may have it too close. Try moving the Leslie away from the console. A typical problem is the slow motors inducing hum into the organ's matching transformer. The MT is located on the bass end of the organ. The slow motors generate much more 60cps radiation than the fast motors.</p>

Geoelectro
</p>

[okdk]

Is the Leslie located on the bass end of the organ? You may have it too close. Try moving the Leslie away from the console. A typical problem is the slow motors inducing hum into the organ's matching transformer. The MT is located on the bass end of the organ. The slow motors generate much more 60cps radiation than the fast motors.</p>

Geoelectro
</p>

</p>

Not really, the leslie is behind me when I play and to my right a bit, maybe 6' from the organ</p>

[geoelectro]

OK. Then I would suspect something to do with the AC that turns on the relay (for slow) entering the audio lines. All these lines are inside one cable. The 122 type uses a balanced line so they reject outside interference naturally. However, the 147 type uses a single ended line which IS susceptible to outside interference. Years ago, Leslie made cables with the signal wire wrapped in a shield. All Leslie cables are unshielded these days and allow for outside interference on unbalanced lines.</p>

You could try making sure your cable is not coiled up or otherwise laying on itself. </p>

Making as short a cable as will go between instrument and speaker. </p>

Building your own cable that shields the signal wire.</p>

Also make sure your organ output is as hot as possible by lowering the Leslie input volume. This gives you better signal to noise ratio.</p>

Geoelectro
</p>

[okdk]

OK. Then I would suspect something to do with the AC that turns on the relay (for slow) entering the audio lines. All these lines are inside one cable. The 122 type uses a balanced line so they reject outside interference naturally. However, the 147 type uses a single ended line which IS susceptible to outside interference. Years ago, Leslie made cables with the signal wire wrapped in a shield. All Leslie cables are unshielded these days and allow for outside interference on unbalanced lines.</p>

You could try making sure your cable is not coiled up or otherwise laying on itself. </p>

Making as short a cable as will go between instrument and speaker. </p>

Building your own cable that shields the signal wire.</p>

Also make sure your organ output is as hot as possible by lowering the Leslie input volume. This gives you better signal to noise ratio.</p>

Geoelectro
</p>

</p>

The cable was coiled up so I stretched it out, didn't help. Is there an output control volume on the organ?</p>

[geoelectro]

No. Playing it loud is your output control. Have you re-capped the Leslie amp? There are some caps in there that if leaking, could be causing your problem. Also, look for the "death caps" to see if you have them. Try removing them if you do. I had a case where we had to install those caps to remove hum. Do that at your own risk. [;)]</p>

Geoelectro
</p>

[okdk]

No. Playing it loud is your output control. Have you re-capped the Leslie amp? There are some caps in there that if leaking, could be causing your problem. Also, look for the "death caps" to see if you have them. Try removing them if you do. I had a case where we had to install those caps to remove hum. Do that at your own risk. [;)]</p>

Geoelectro
</p>

</p>

Seems like I should replace the caps, probably should be done regardless of it fixing my problem. I see kits available with caps, resistors, and a can, is this the way to go?</p>

[geoelectro]

Yep. Only one resistor is required. A 470 ohm 1/2 watt.</p>

2) .015 @ 600Vdc</p>

4) .1 @ 600Vdc</p>

4) .005 @ 1600Vdc.</p>

1) Filter can.</p>

If you have any problems finding this stuff... email me.</p>

george@bentonelectronics.com </p>

Geoelectro
</p>