760 No bass output

[kingsboard]

Hello, Hope everyone is hanging tough & doing well.
Got a 760 for a really good deal because there is no sound coming from the 15 " Bass Speaker.
The Horn sound is great.
I hooked up another known working speaker, but got no sound.
What do you all think I should do first?
(I really want to throw a tube amp in there, but.... )
Thanx in advance ya'll

[David Anderson]

For one thing, this 760 has definitely been messed with. An entire circuit board is missing, the crossover, which should split the signal into Bass/Treble upstream of the amp boards. Also, the fast/slow motor stack for the lower drum has been removed and replaced with a single-speed fast motor from an older Leslie.

I'm not even sure I see the mounting studs that should be there for the crossover board, so the whole amp panel may be from some other SS Leslie. A normal 760 does not have those speakers on the sides. You may have something cobbled together from someone's collection of spare parts.

[tpappano]

Is the bass rotor installed upside down? Looks a little odd ...

[kingsboard]

I should have figured cause it was cheap.
Ok. I (We) Lol, shall deal with it !

[David Anderson]

The power amp driver modules appear to be from 1974.

In a 760, there should be a third circuit board above the Bass and Treble driver boards. Does it look like something was there at some point? There should be stand-offs for mounting it.

[kingsboard]

Thanks for your observations David
Does not look like any standoffs or anything was ever mounted above the driver boards.
This lower back plate doesn't look like its from a 760.

Here are pics of the Lower back plate with Driver boards - Front & Back

[Drawbar Dave]

Looks like crossover and 6X9's from a 710 or rotosonic Leslie. I can sell you the missing crossover board and a new lower panel if it helps.

[Jyvoipabo]

Hello,

I mounted by myself a tube amp for the treble on a 760 and it improved the sound a lot.
From memory, it was a reverb amp from a 147RV that I managed to fit behind the PSU.
But I kept the original transistor amps for the woofer.

In your case the cross over is missing. You should know where the single red and orange wires come from inside the power supply.
For cheking the amp, you can unplug them and lightly tap the pin with the tip of a screwdriver.
If the amps are good then you should be hearing something from the speakers.
Chek also the temperature of the power transistor and the condition of the white capacitors.

JP

[David Anderson]

That amp panel never had any mounting hardware for an electronic crossover board, so it was not originally from a 760. It was from some other SS Leslie model like the 710, which had two power amp channels, but no electronic crossover board.

[Jyvoipabo]

Thanks David
I learn quickly with you.

It is therefore an amplifier of 710
Which have 2 inputs.
Amphenol Pin2 = Rotary chanel.
Amphenol Pin4 = Stationary chanel (15 'speaker and passive crossover)

On the 760 There is only one input :
Amphenol Pin2 = Signal In
Amphenol Pin4 = Not connected.

So if you use a pedal designed for a 760. Then nothing comes out from the bass and that's normal.

JP

[Goff]

Curious as to what the stylized(?) side vents for the 6x9's look like on this.

[kingsboard]

Here you go Mr Goff B-)
nothing special.

[David Anderson]

So those 6x9 speakers are just mounted to the inside of the cabinet with no vents to the outside? Someone had a sense of humor.

[kingsboard]

I was thinking the same thing. I'm gonna pull em out and install em in my dear ole Dad's 69 Chevy !

[Drawbar Dave]

So those 6x9 speakers are just mounted to the inside of the cabinet with no vents to the outside? Someone had a sense of humor.

They are attached to the reinforcement panels for the recessed handles, yet there is no evidence of handles ever having been fitted. I wonder whether the cab has been re-covered at some point.