Mark IV - reverb malfunction

[GJV]

Hi all Boogie lovers I bought one Mark IV, B, short head last week here in Europe and I can honestly say I´ve just found my favourite sound. This amp really kicks *** and I´m kindly surprised from all possibilities in the setting´s combinations. I´ve tried Mesa Formula Pre, Dual Rectifier, lot of Marshalls, some Laneys and some Soldano SLO circuitry inspired amp but Mark IV is the best for me! Hope I´ll be happy for a long time with that sound ;o)

But... When I´ve tried to connect classic one-way footswitch into the reverb input (rear panel) there was no function at all. After disconnection the footswitch from the reverb input the reverb doesn´t work (!!!)... even I hear some little scratchy and random noise... I´m confused (this is my new amp).

Do you have some experiences and ideas where the problem can be? And what should I do with this? I hope it´ll be some easy problem... Thx 4 help!

 

[Boogiebabies]

First, check all the cables.

Either the jack's shorting tab is stuck open or you have a bad preamp tube in the V3 or V4. Now, this is speculation as you never stated that the reverb worked to begin with. Stick a different footswitch in the reverb footswitch jack and see if it comes back. If not, and it continues to make noise try the preamp tubes.

 

[boogietone]

My reverb on my MKIV A version went out. Ended up being a broken black wire inside the reverb tank. Ordred a new tank from Accutronics and reverb is good as new. Good luck on yours!

 

[GJV]

Thanks guys for your opinions! I can eliminate the cables - it was the first thing I checked out, but I didn´t find anything on it. I´ll try to look at the other possibilities (described by Boogiebabies) over the weekend, cause I´m working all day long this week, so I´ll post my checking results here on Sunday evening. Thanks again and see ya!

 

[hydesg]

i felt that the reverb on my mark iv is kinda weird

it seems like the more i inscrease the reverb
the more trebly it gets
is it normal?

if i were to turn off the reverb it sounds great though

 

[Boogiebabies]

i felt that the reverb on my mark iv is kinda weird

it seems like the more i inscrease the reverb
the more trebly it gets
is it normal?

if i were to turn off the reverb it sounds great though

From experience, that phenominon is typical of Mesa MK series amps. The IIC'+s, III's and IV all seem to give the tone a bit more bight and treble. They all have a cap that is supposed to bleed some of those highs off. The IIC+ and III is .01 and the IV is .005. Audibly, the MK III should have, and in my opinion does, have the thickest reverb. Mesa used a .003 cap on the input stage to cut some highs there as well, but in a slightly different way. The MK IV also has it's reverb input signal sent through the channel masters which get switched on in the circuit through LDR's which are known to have a about 5pf of capacitance as well. The IV has by far the most controlled reverb of the MK series as it is designed to control the amount of level from R1, R2 and Lead. It's not perfect, but at least you don't go from a mild reverb on the lead channel to a loud washed surf on clean.

 

[hydesg]

would it be better for me to use an external reverb unit like the gmajor instead? and leave the tone raw on the mark iv?

ive been contemplating getting that rack unit for quite a while

 

[Boogiebabies]

would it be better for me to use an external reverb unit like the gmajor instead? and leave the tone raw on the mark iv?

ive been contemplating getting that rack unit for quite a while

Same here, but I have been holding on the a purist mentality since I dropped the rack in 1992. Worst case scenario these days is guitar, cord ,BB Preamp and a TC Electronics SCF. Mostly, it's guitar, cable and amp, but I am struggling not to add the G-Major and probably will.

 

[GJV]

I don´t know where the problem was indeed, but I checked the cables again and checked reverb footswitch input too before switch-on the amp and the reverb has seemed to be OK, so it´s a mystery what has really happened

 

[Bartolus]

My reverb on my MKIV A version went out. Ended up being a broken black wire inside the reverb tank. Ordred a new tank from Accutronics and reverb is good as new. Good luck on yours!

Which one did you ordered? Which would be compatible with a Mark III short head?

Antique Electronic Supply?

Thanks

B.

 

[boogietone]

My reverb on my MKIV A version went out. Ended up being a broken black wire inside the reverb tank. Ordred a new tank from Accutronics and reverb is good as new. Good luck on yours!

Which one did you ordered? Which would be compatible with a Mark III short head?

Antique Electronic Supply?

Thanks

B.

It was P/N 9AB2A1B. I bought it off Ebay from Sepigroup I think was the name of the company.

I don't think it would be compatible with a MKIII shorthead only because of the physical dimensions of the tank. I tried to swap my MKIV combo into my MKIII shorthead shell but quickly discovered the cutout in the MKIII head shell for the reverb tank was way too small. Accutronics makes smaller dimension reverb tanks though that would fit. You just have to get the specs for it. I just used the part number off the one I replaced.