Leslie 147 60hz HUM - Troubleshoot.

[Guest]

Hello everyone,

please forgive my newbie-ness.

I have a 147 that has a non-original 2 prong AC cord and was wondering how to eliminate the 60HZ hum that is coming out of it with/without my Hammond connected.

what are the steps I should take to try and get it to be less hummy?

is grounding possible (and where?)

Thanks for taking the time to read my post and have a great day!

[Sweet Pete]

Welcome to the Forum

147 has a load resistor switch to compensate the various loads(output impedances/instruments) it sees on the inputs of pins 1 and 6.
Three settings are :
1.Open
2.8 ohm
3.16 ohm
Try matching your 'input' impedance with this dial.
Open setting without an input load is a source of hum for sure.

Pictures of the 're-engineered' 147 interface and your Hammond,and whatever else you intend to route through the 147 should be of interest to those trying to help.
Main thing is,pins 1 and 6 like to see a speaker level load.The speaker outs of a Fender Twin Reverb are among favorites for a speaker level interface to a Leslie.

You can glean much info from the Leslie pages on Captain Foldback,and learn your stuff there pretty much.A 147 Leslie is a W type hookup.

Let us know how you do,it could be just a dial in the wrong setting.

[nonreverb]

Is this 2 prong cord connected directly to the Leslie?

[Drawbar Dave]

Also what kind of Hammond are you attaching to the Leslie? Does it have built in speakers and a main/ensemble/echo switch?

[Jyvoipabo]

Hello,

Usualy the 147 is powered (Amphenol Pin3 and4) and also grounded (Pin1) by the cable going from the organ.
It don't need another connections to ground.
Worse adding a ground connection could create a ground loop and the hum that goes with it.
Note that this hum will increase as you turn right the volume control of the amp. But sometimes it can be considered acceptable

If you power your 147 in another way.
For safety you can add a ground connection screwed anywhere on the chassis of the amplifier.
But, the ground loop problem will remain the same.

If the hum is not sensitive with the volume control, your amplifier have problem.
You will have to take out the diagram and do some checks.

JP