Mk IIb Reverb Ft/Switch wiring

[Harry the Horder]

Hi, One last issue with this Mk IIb can anyone tell me the wiring for the footswitch it is not shown on the circuit diagram and I think mine is wrong!! I know the sleeve is shared with the EQ as a common earth but I can't see at what point to wire in the pos or hot side for switching reverb into the circuit any ideas??

 

[Boogiebabies]

Harry,

Check your e-mail.

 

[Harry the Horder]

Hi all,
Thanks for the chassis photo.unfortunately it does not clearly show the wiring only highlights the fact that mine is completely up the wall.
If no one can tell me can anyone post chassis pictures of MkIIb innards mainly showing the Footswitch wiring in glorious Technicolour I can then zoom in and work it out.Thanks in advance.get those pictures coming.Harry

 

[Harry the Horder]

I'm wondering now what gives? on the circuit diagram the only foot switches shown are for EQ and Gain Boost and no Reverb are some wired up so that these are switchable and the Reverb is permanant?
I still need to know the wiring Please!!!

 

[Harry the Horder]

Bumpy Bumpy!!

 

[Harry the Horder]

Well I seem to be talking to myself I think I've finally cracked it. See if you follow my logic. :idea:
On the MkIIb they come either with or without EQ those fitted with Reverb/EQ will be wired up to the foot switch socket for switching these in and out those that don't have the EQ fitted will be wired up to have the Gain Boost/Reverb wired up. On my Chassis there is an additional RCA Socket this is for the Gain Boost switching and actually written on the top of the chassis by this defunct socket is the initials MD I took this to be someones initials but after a lot of hair pulling :idea: :roll: :lol: I have come to the conclusion it stands for MID!! 8) ( that being the point the gain boost wire goes to) does this sound right ? has anyone else got this fitted ? It's just a matter now of rewiring it all up and away I go.
Is there anybody out there??

 

[Harry the Horder]

I guess I'm all alone then.Bump

 

[Harry the Horder]

I'm still lost on this wiring for reverb/eq footswitch. any takers out there please.

 

[Boogiebabies]

Check your E-Mail.

 

[Harry the Horder]

Many thanks Boogiebabies for the gut shots unfortunately as is typical the bit I wanted to see was obscured by wiring.I have finally worked it out I hope so this is it!!
The gain/boost goes to an RCA Socket located on the chassis just one wire from the mid pot. ( this was wired to the other socket and was permanently on)
The Reverb wire comes from the junction of a .003 cap/100k pot and shunts down to earth when activated by the foot switch if no footswitch is plugged in it will stay on permanent. this is wired to the ring of the plug just the one wire.
The EQ should be wired to the Tip and the Black wire from the filter caps wired to the Breaker.this is so that when no pedal jack is in it still makes contact so the EQ works. so all I've got to do now is rewire my actual pedal for ring and tip as these are the wrong way round hence some of the confusion and wire the rest up as described.Easy in it!!
Many thanks once again.fingers crossed!!!

 

[Harry the Horder]

Once I'd re-wired still no Reverb this latest problem stemmed from the Grey RCA plug for the reverb springs once changed all works OK.
I'd like to thank Boogiebabies for taking the time and effort to help me
My band will be gigging in Belgium/Holland on the 27th December at a place called Venray ( De witte Hueve ?) something like that. come and say Hello I owe you a Beer many thanks Harry

 

[asmith9509]

Hey Harry- I'm trying to get the reverb working on my IIa. Which RCA plug did you replace- the one that terminates at the amp chassis or the one that terminates at the reverb tank? Did you replace the cable, or the RCA jacks?
Just trying to work down the possible solutions for my non-functioning reverb, from easiest to hardest (Occam's razor).

 

[asmith9509]

One other thing... when I finally get the reverb working, I plan to build a custom footswitch that uses a single run of four-conductor cable and has the switch for rhythm/lead, gain, and reverb all on the same box. Anyone considered this, or have any helpful tips? Seems like both footswitch jacks share a ground plane (no resistance reading between the two).

 

[Harry the Horder]

Allo matey!!
I could not find anything wrong but having read about someone else having a bad RCA plug ( the moulded one ) I thought I'd go for that first.
It's the grey lead that plugs into the chassis end I don't think the other end gets disturbed that much so is best left alone.
I would think your plan with the foot switch should work as they seem to share a common earth ground out system just suck it and see.I'm not sure about the Lead/Rhythm but definitely the Mid Boost, Graph EQ and Re-verb could use the same shielded wiring.

 

[Harry the Horder]

Ref that Lead/Rythm switch I think for that one you have to have two wires going to it not a + and ground well that's what I've read on ere' but I have not got round to checking it out yet.

 

[asmith9509]

Harry- thanks for your help.

So... my attempts to get the reverb working have been in vain. I have replaced V3 (from what I can tell V3b is the reverb send) and V4 (reverb return); cleaned all of the RCA jacks and cable plugs with DeOxit and DeOxit Gold; even tried a different RCA cable that I knew to be fine. None of these things worked. Interestingly, if I turn the reverb knob up and give the tank a bump, I can hear the spring echo playing through the amp; perhaps the return side of the circuit is working but the send side is not. Might be time to take it to a proper amp tech.
With respect to my footpedal project- the rhythm/lead footswitch is a single switch in a box, using mono (2 conductor) cable to a jack on the front. the other footswitch has the gain and reverb switches, and uses a stereo cable with a common ground to a jack underneath the chassis. There was no measured resistance between the front panel mono jack and the underneath stereo jack; I'm thinking they must be a common ground. Therefore my four conductors would be:
1) ground (shield)
2) rhythm/lead (conductor 1)
3) gain (conductor 2)
4) reverb (conductor 3)

Can't think of any reason why this shouldn't work.

 

[Harry the Horder]

Have you got another amp with reverb? Try plugging the RCA cables into that if you have and that would eliminate the Pan or Amp. Did you check the wiring as I suggested? it might be permanently shorted down to earth as the previous owner maybe did not want to use reverb.
Looking at the schematic you are right and it should work and you need yet another wire for the EQ on/off function.

 

[Dalibor]

Hello from Czech Rep )

I had the same problem with my MKIIb's reverb (MKIIb 12/20/80)

My tech had cleaned reverb springs in a centre of a reverb tank - they were muffled by a heavy dirt of oxidized foam molitan pads there - e.g. mechanical problem ... - 30yrs is 30yrs )))...now it's OK.

Maybe you'll have the same problem...

Good luck

Dalibor