Mark IIB Reverb and Footswitch

[ElPedro]

I've been reading about the 2B, and the footswitch...And I'm still confused. A guy brought me one of these amps to fix up for him, but has no footswitch, and says he gets no reverb (amongst many other issues).

Prior to digging into the reverb circuitry, I'd like to gain an understanding of where the footswitch connects to on this amp.

This particular model has no EQ, only reverb.

If I plug a mono plug into the "footswitch" jack on the front of the amp, I get the amp to switch channels.

Now on the underside of the chassis as the two 1/4" jacks that baffle me. I've tried a mono and stereo plug in both (not at the same time though), and cannot get anything to happen except getting the amp to significantly quiet down.

At no time during my testing have I had any guitar signal going through the reverb. But if I give the tank a decent thump I can get the springy reverb sound to come through. However, I cannot turn the reverb "off" unless I turn the reverb pot to 0. My understanding is one of these jacks should handle this.

Anyone have a definitive answer or pictures of what plugs in where on this thing?

Thanks in advance!

 

[gts]

Deleted due to.....

Ignore the Mark III configuration. THIS WILL CONFUSE MORE since you say you working on a Mark IIB.

Mark II and Mark III are way different animals from each other.

 

[gts]

Also if he says he's getting no reverb this simple fix might help:

 

[ElPedro]

Thanks guys.

The thing is, I'm not sure if I am getting reverb or not. I can smack the tank and get some reverb, but not like I'd expect or have heard from other amps when smacking the tank. I also get no guitar signal thru to the reverb. So I'm not sure if reverb is really turned on or not.

My assumption is that as I don't have both EQ and Reverb, that my plug on the underside of the chassis should be mono, and shorting that plug should either turn the reverb on or off.

If memory serves me, the jack marked "rhythm 2" on gts' drawing does cause some sort of gain change when I short a mono plug out in that jack.

If I short a mono plug out in the jacked marked "eq/rev", the amp simply goes earily silent.

 

[lovetoboogie]

On your Mark II-B, one of the jacks is a 1/4 TRS Stereo Jack for Reverb/Pull Boost(On models without GEQ), the other jack is a "Preamp Out" that taps the signal just after the master volume...

You don't need a footswitch to operate the reverb. It is not a 'shorting' jack and therefore the reverb defaults to 'always on' with nothing plugged into it...

Your lack of reverb, or weak reverb problem lies elsewhere. Some likely culprits are: RCA cable jack ends not making good contact either on the tank end, or the chassis end, reverb driver and/or recovery tube bad, bad reverb tank, poorly seated reverb control pot(needs to be snug on the chassis for good ground), etc...

Since you hear the telltale sound of the tank making noise when you whack the amp it seems the problem is on the driver side of the circuit...

 

[RR]

On your Mark II-B, one of the jacks is a 1/4 TRS Stereo Jack for Reverb/Pull Boost(On models without GEQ), the other jack is a "Preamp Out" that taps the signal just after the master volume...

You don't need a footswitch to operate the reverb. It is not a 'shorting' jack and therefore the reverb defaults to 'always on' with nothing plugged into it...

Your lack of reverb, or weak reverb problem lies elsewhere. Some likely culprits are: RCA cable jack ends not making good contact either on the tank end, or the chassis end, reverb driver and/or recovery tube bad, bad reverb tank, poorly seated reverb control pot(needs to be snug on the chassis for good ground), etc...

Since you hear the telltale sound of the tank making noise when you whack the amp it seems the problem is on the driver side of the circuit...

This ^^^^!

Ignore the Mark III configuration. THIS WILL CONFUSE MORE since you say you working on a Mark IIB.

Mark II and Mark III are way different animals from each other.