Mark IV A - Presence and Pull Shifts not working

[michelj]

I just joined the forum about a week or so and have already gotten some good advice on a reverb problem that I was having with a Mark IV A short Head that I recently purchased.

I have completely retubed the amp with stock Mesa pre-amp and power tubes. It sounds great and is working fine except for the three presence knobs and the pull shifts on R2 and LD. None of these have any effect on the sound being produced by the amp. I've read all the posts relating to presence controls and pull shifts and didn't find anything that might give me a clue as to what is wrong here.

Unless some of you can come up with some easy fixes for a non techie, I'll have to bring the amp to a tech and let him have a go at it.

Thanks in advance for your attention to this matter.

Michel

 

[jamme61]

It sounds like tech time IMHO. I'm not a tech either but it might be worth pulling the chassis and see if it's a simple fix, like a wire came loose. You never know. I don't mind paying the tech to fix it, I mind losing my amp for two to three weeks. Be carefull to drain the caps so you don't electrocute yourself.

 

[michelj]

It sounds like tech time IMHO. I'm not a tech either but it might be worth pulling the chassis and see if it's a simple fix, like a wire came loose. You never know. I don't mind paying the tech to fix it, I mind losing my amp for two to three weeks. Be carefull to drain the caps so you don't electrocute yourself.

Thanks for your response jamme61.

I'll drain the caps, pull out the chassis and see if there's anything obvious by following circuit and schematics. If I don't find anything simple, it's off to the tech. I agree it's a bummer losing the amp for a few weeks especially when I'm just starting to get acquainted with it.

Michel

 

[michelj]

Well, I looked inside and found the culprit. The .1M 100v capacitor (Z5U manufacturer part #) that should be soldered to the R1 presence knob is just dangling there. It has broken off. I'm off to the electronics part shop to pick up a replacement and get my presence back.

While I was looking inside, I noticed that there's a date of 5-1-92 (initials MS) on the main board close to the input jack. I suspect that must be the build date.

Good stuff!

 

[jamme61]

that's awesome! I love when that happens. my mkiv is newer and when I opened it up there was no dates. my mkiv is tough but I think I'm getting there.

 

[michelj]

that's awesome! I love when that happens. my mkiv is newer and when I opened it up there was no dates. my mkiv is tough but I think I'm getting there.

Hello again,

the part cost me about $3.00 Cdn taxes in and it took me about five minutes to solder. I also bought a bottle of compressed air and squirted out some dust. I did a quick check to make sure that everything worked ok and then put the chassis back in the head cabinet.

Speaking of the head cabinet, it has a MESA Engineering plaque on the front grill instead of a Boogie plaque as seen on heads and combos or MESA/BOOGIE on the bottom portion of the rackmounts. What's with that??? I wonder if I possible have Mark IV that started life as a rackmount or combo and ended up as a head. I don't know if Mesa Boogie would have the records to indicate how this amp started off as. I think I'll send them an email.

Yeah, the Mark IV has so many tonal possibilities that it's going to take quite a while to nail everything done. I'm in a classic rock band so I'm in the process of trying to dial in a nice clean tone on R1, a mildly distorted crunch tone on R2 and then some smooth distortion on LD. We don't play any metal so I'm keeping the knobs away from 10. Up to now it's been alot of fun and a great learning experience. This is bar none the best amp I've had to date.

 

[jamme61]

Yeah, the Mark IV has so many tonal possibilities that it's going to take quite a while to nail everything done. I'm in a classic rock band so I'm in the process of trying to dial in a nice clean tone on R1, a mildly distorted crunch tone on R2 and then some smooth distortion on LD. We don't play any metal so I'm keeping the knobs away from 10. Up to now it's been a lot of fun and a great learning experience. This is bar none the best amp I've had to date.

Wow that's me too. I just p/u a Weber mass lite because the amp is so loud. I was using channel 1 any where from 5 to 10 pulled and channel 2 no higher then 5 (not pulled ) I want my fender on channel one with a little grit and my Marshall plexi sound on channel 2. I'm getting close but it's tough. A lot of guys here are into metal, which is great except for me getting info on classic rock tones. When I look at some of the settings listed and they have channel 2 at 10 and pulled, that's just way off from what I'm looking for or can even use at the gig. I put a bright cap on channel 2 (100pf) which is on when 2 is not pulled. I was trying to get a little more cut and detail out of 2. I think my problem is when your ears hear channel 1 and it's so open with a lot of detail to it, and then you switch to 2 and because of the extra gain it lose some tone. I think I'm getting a really good tone from both channels but when I switch from one to two it a little tough. I think channel 3 is great, I haven't dialed in a bad tone yet. It's a great lead sound that makes it easy for even me to play lead. Lately I've been trying to dial in more of a blues lead on three, which sacrifices some of the sustain. Sorry to go on so long. Good luck

 

[michelj]

Yeah, the Mark IV has so many tonal possibilities that it's going to take quite a while to nail everything done. I'm in a classic rock band so I'm in the process of trying to dial in a nice clean tone on R1, a mildly distorted crunch tone on R2 and then some smooth distortion on LD. We don't play any metal so I'm keeping the knobs away from 10. Up to now it's been a lot of fun and a great learning experience. This is bar none the best amp I've had to date.

Wow that's me too. I just p/u a Weber mass lite because the amp is so loud. I was using channel 1 any where from 5 to 10 pulled and channel 2 no higher then 5 (not pulled ) I want my fender on channel one with a little grit and my Marshall plexi sound on channel 2. I'm getting close but it's tough. A lot of guys here are into metal, which is great except for me getting info on classic rock tones. When I look at some of the settings listed and they have channel 2 at 10 and pulled, that's just way off from what I'm looking for or can even use at the gig. I put a bright cap on channel 2 (100pf) which is on when 2 is not pulled. I was trying to get a little more cut and detail out of 2. I think my problem is when your ears hear channel 1 and it's so open with a lot of detail to it, and then you switch to 2 and because of the extra gain it lose some tone. I think I'm getting a really good tone from both channels but when I switch from one to two it a little tough. I think channel 3 is great, I haven't dialed in a bad tone yet. It's a great lead sound that makes it easy for even me to play lead. Lately I've been trying to dial in more of a blues lead on three, which sacrifices some of the sustain. Sorry to go on so long. Good luck

Hello Jamme61,

yup the amp can be plenty loud. You can tame it down by using tweed power, class A and triodes. That's what I've been doing for the last few days and it allows me to stay in the same room :wink: . Class A does make the R1 a little bit more prone to grit up earlier but at this point I'm willing to live with that in order to be able to get some tones that aren't completely deafening level wise. As I said earlier, I've having so much fun right now that I must be doing something illegal lol,

Michel

 

[jamme61]

The lowest volume, I got, was all 6v6's in class A with tweed power. Channel 1 starts break up even more, at that point. I just got the attenuator today, but I think it's going to be just what I needed. This is the first night my ears won't be ringing when I go to bed. Have fun