Peavey Classic 30 head with humming reverb.

[booj]

I replaced a missing reverb tank, an Accutronics 4EB2C1B. I've checked the tank and get about 59 ohms DC at the input and about 218 ohms DC on the output. That seems kinda low on the input since it goes directly to the output of the reverb chip.
The problem is 60 HZ hum that is only affected by the reverb knob and is there regardless of whether there is an input to the amp.
I've tried the reverb out with the amp outside the box with no difference.
I've also checked my connections to the amp and they seem to be correct
Clues? Ideas?
Thanks for your time!
peaveyclassic30.pdf

[Enzo]

Does the reverb function, other than the hum? Does it seem more or less normal other than the hum?

The resistances sound right, remember the circuit sees impedance, not resistance.

Pull the return cable out of the OUTPUT jack on the pan and short across it. ANy effect on the hum?

Disconnect the molex connector for the reverb cables inside the amp. ANy effect on hum?

The whole circuit is reverb pan, cables, connectors, and the 4558 IC. Short across the return pins of that Molex, any hum abatement?

If it is not in the cables, then try a new IC.


And for that matter, the IC needs clean DC power. It runs single supply off -30v, with signal referenced to -15, check all that.

[booj]

thanks for your response Enzo! I'll try a new chip, measure some stuff once the board is out and get back to ya

Pull the return cable out of the OUTPUT jack on the pan and short across it. ANy effect on the hum?

No hum

Disconnect the molex connector for the reverb cables inside the amp. ANy effect on hum?

No molex connector. I forgot to mention that was missing also. I directly soldered the cable leads of some standard molded plug RCA stereo connectors to the pins.

The whole circuit is reverb pan, cables, connectors, and the 4558 IC. Short across the return pins of that Molex, any hum abatement?

[COLOR="rgb(255, 140, 0)"]Same as shorting the cable itself. No hum.[/COLOR]

If it is not in the cables, then try a new IC.

sounds like the plan


And for that matter, the IC needs clean DC power. It runs single supply off -30v, with signal referenced to -15, check all that

It's getting _32 and -16 at the respective proper points. supply looks clean.

[booj]

Boy, the greens hard to read ain't it

[Enzo]

OK< first item then. SHorting the return cable kills the hum? Then I'd have to say that is where it is coming from.

Did this hum arise after soldering those wires to the pins? What is the possibility the conductors were reversed on the pins - shield for signal lead? On the Molex pins, there are five places for four pins. One empty space. The lonesome end pin is the hot for the return, and the first pin after the gap is the ground for that shield. I hope we soldered directly to the pins and did not take any shortcuts to ground.

Make sure we are plugged into the correct jacks on the pan. The reverb will work half-assed if backwards, but the drive end jack - the INPUT jack - is NOT grounded to the pan. So if used as an output, it will hum.

If you have any other 4EB pans, try connecting a different one, what the heck.

[oc disorder]

Make sure the return end or output on the tank doesn't sit below the power transformer
or it will hummmmm !
The two shields go to the inner pins the hot wires to the outside see attached masterpiece !


PS the new forum layout/skin is rather a dramatic change !
Like a valve amp to a digital one !

[booj]

Thanks oc disorder. I have just realized the problem IS with the orientation of the reverb pan. It wasn't humming at all outside of the box AFTER I had changed the chip. It seems that it did hum before I changed the chip. Maybe circumstantial.
Anyway, I take it that the leads going into the reverb tank should be facing the front mounting board and not the amplifier chassis.
Oh well, second time around usually goes faster.

[Enzo]

Wherever they point, in any amp, the reverb pan should be oriented to put the OUTPUT end as far from the power transformer as possible.

[booj]

That's true Enzo and that's what fixed the problem (which I probably created by orienting the pan the wrong way to begin with)