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On Thu, Apr 20, 2023 at 11:59, Chris Clifton

<clifton.christopher@...> wrote:

To dumb it down to absolute basics. Connect a 16 ohm 20 watt resistor between the hot signal feed in your modified 22H amp and ground. If your modifications have made the signal input 100% compatible with a standard 147 system, this will be between pins 1 & 6 of the six pin input connector on the Leslie amplifier chassis.

On 20/04/2023 16:54, Chris Clifton wrote:

A standard 147 type amp has two 8 ohm 10 watt resistors and the console load switch with three settings, open, 16 ohm and 8 ohm. The open position would only be used in installations with multiple Leslies, only one Leslie would need to have a load set, all the others would be left at open. In the other two positions, either one resistor, or both in series are connected across pins 1 & 6 of the six pin connector. Pin one is signal ground and pin 6 is signal. All you need to do is wire a suitable resistor, minimum power rating 10 watts, and a resistance comparable to the impedance of the built in speakers of the organ. In practice, although 147's give you the option of an 8 or 16 ohm load, just going for 16 ohm works well. A quite frequent call out back in the day was, "The Leslie hums when iI switch to main". The cause, almost always was that one of the load resistors had burnt out. Replacing the burnt out resistor cured the problem, switching to 16 ohm prevented recurrence for two reasons. 1) I now had two resistors with a total power rating of 20 watts in circuit instead of just one 10 watt resistor. 2) The 16 ohm load drew less power from the organ amp anyway. Most amps, either valve or transistor are perfectly happy with a nominal load twice of the usual value.

On 20/04/2023 15:33, john alluneedtoknow via groups.io wrote:

Thank you Chris, I did overlook the resistor and studying the schematic I am unclear exactly how to add it. Would you be able to dumb it down a bit for me?

Thank you in advance,

John

On Thu, Apr 20, 2023 at 3:40, Chris Clifton

<clifton.christopher@...> wrote:

The 147 will have a console load resistor in it. Does the modified 22H have the equivalent? 147 type Leslies will hum when the MEE switch is set to main if the console load resistor is set to open or burnt out. If you didn't provide such a resistor when modifying the 22h it will also hum when the switch is set to main. Without a load resistor, the Leslie amp has a high input impedance, perfect for allowing the unscreened signal lead sharing the cable with mains wiring to pick up hum.

On 20/04/2023 02:19, john alluneedtoknow via groups.io wrote:

Gentlemen;
? I recently installed a rebuild kit in the 22H amp because the owner said there was a loud hum from the amp. Upon completion I tried the amp and it was very quiet and running well. A few days later the irate owner called to say it was still humming. I had him bring it back and I hooked it up to find it was running nice and quiet as when it left the first time. I began to ask questions and discovered he was trying to use it with an 1147 Leslie control box which of course is incompatible. I rewired the plug on the Leslie amp to make it compatible with the box (not my first choice) at which time he took it home and said it was still humming. He claims the box works fine with his 147 so I must have missed something but I haven't been able to figure out what. Any ideas?
Warmest regards,
John

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