Mark IIb with two reverb knobs?

[Jbc72223]

Yesterday I picked up a 100/60 watt mark IIb without the graphic eq with the date 3/17/81 written inside the chasis. I got a slanted 4 x 12" cab with it that has a plate that says "boogie" across the front loaded with "force" speakers (the guy at gc said he thought it was an old school EV speaker). If anyone could tell me anything about these speakers I'd appreciate it because I basically know nothing. (I'd like to sell the cab and get a 2x12 anyway because the 4x12 is just too monstrous to bring around).

The reverb control (next to the presence knob) on the back of the amp has been pulled out and someone put a metal piece over it that fits almost perfectly into the hole where the knob was(which makes me wonder if the last owner had a tech do some real work on it). The funny part is that there is actually another reverb knob on the front of the amp but it does not work when I turn the knob.

I would really appreciate any suggestions to get the reverb up and running. Could it just need a new tube in V4? I know I should really send in the amp to Mike B for a full check up and retube it being that the amp is over 25 years old and I have no idea whats been done to it but I simply don't have the money at the moment.

BTW, I picked up the head for 600. and the cab for 300. I think I got a good deal but you guys would know better.

 

[Ultron]

good deal on the cab....head seems like a decent price. I paid $725 for my IIB combo...although the Mark prices are all over the place really...not sure what the real value is anymore.

I sent mine to Mike...he did full recap, fixed some pots, replaced all the graphic EQ sliders, tweaked reverb, and the FX loop mod (which greatly improved the lead channel). Amazing cleans on the IIB, very underrated amp. Listen to Ozzy's "Speak of the Devil" cd to hear IIB heads run into greenback cabs....sounds monstrous.

 

[Jbc72223]

How much did mike charge you for all that work? Did you ask for the recap and pot work or did he repair it when he thought it needed it? In what way did the effects loop mod change the leads? (less muddy i hope)

Thats a pretty sick tone on the ozzy cd. The cleans on the IIb are amazing though. It sounds like a deluxe reverb with better punch and it sits a little better in the mix (fenders almost jump out too much for me).

the Mark prices are all over the place really...not sure what the real value is anymore.

Theres a guy on craigs list claiming they go for 2500$. http://littlerock.craigslist.org/msg/775448006.html

 

[Ultron]

How much did mike charge you for all that work? Did you ask for the recap and pot work or did he repair it when he thought it needed it? In what way did the effects loop mod change the leads? (less muddy i hope)

Thats a pretty sick tone on the ozzy cd. The cleans on the IIb are amazing though. It sounds like a deluxe reverb with better punch and it sits a little better in the mix (fenders almost jump out too much for me).

the Mark prices are all over the place really...not sure what the real value is anymore.

Theres a guy on craigs list claiming they go for 2500$. http://littlerock.craigslist.org/msg/775448006.html

I think everything came out to @$300, not including shipping ( I just sent the chassis). Once Mike has the amp open for the mod, the extra stuff he does he just charges for parts.

I hated the lead channel, it had this synthetic buzzy grind to it. Not sure the exact details of the fx loop mod, but it changes the path on the lead channel, removing some sort of bottleneck (someone can chime in here and explain better than me). It was a major fix that occured with the IIC+ amps....the reverb and FX loop were design issues with the IIa (EDIT, no fx loop on IIA) and IIb amps, IIRC. The modded IIB lead chan sounds way more open, less compressed buzzy...very usable. The amp is worth it's money for the clean channel...oh yeah, I think Mike added more headroom to the clean channel too, as if it needs more. :lol:

 

[Buddy]

The first thing you should do is check the outboard components .
Are the 2 wires from the amp chassis going to the lower reverb tank ?
Sometimes they will get switched around and the reverb will go away . Try reversing them , or gentle manipulation /cleaning of the connections can help . If you have a voltmeter you can check for continuity .

Insert a phone plug/swab/scotch bright into the effects send and return jacks with a spritz of contact cleaner on them . Repeat like 5 -10 times . It wont hurt anything , and if the amp cuts out intermittently , its known to fix it .

Still no reverb ? Got any known good 12ax7's about ? start swapping .

It is not unknown for a reverb tank to go bad , and if you don't want to send it out , finding a replacement is easy enough and inexpensive .

Unless you are comfortable with pulling the chassis and braving the 400+ voltages , that's all you can do . (I may have missed something)

Good luck to you . 8)

 

[eldi]

Theres a guy on craigs list claiming they go for 2500$. http://littlerock.craigslist.org/msg/775448006.html

$2500 I think is out of line for a mkIIb, but more in line with what a mkIIC+ is worth.

I'd say $600 is a fair price for a mkIIb, I would expect @ least that much if I was to sell mine..

 

[Jbc72223]

Yea I thought 2500 was a little absurd.

I took out the chassis today to get a good look at everything. Its got the usual "MD" written inside the chassis, and the tube slots are marked. The 4 preamps are positron 12ax7s. The 6 power tubes are Mesa 6l6s (yes the STR415s). Then theres a 6FQ7 tube (Does anyone know what this is?).

I think all the tubes are original or just really old replacements, but the guy who sold it said he hardly played it (which it looked like too). And I doubt he did too much damage to the 10,000+ hours the str415s can run.

Just how rare and valuable are these tubes? Should I take them out and hide them in a closet? Does anyone know if i can take out a pair of these and make the amp less wattage (theres 6 in it btw)? Then I'd at least have a couple spares.

 

[eldi]

6 6L6's ehh? Sounds like you got a coliseum head instead of a 60/100....nice score!

You should be running about 150 watts @ full power then...

You got yourself one helluva loud amp sir!

 

[Jbc72223]

Yea its a coliseum alright but it does have the 60/100 switch on the chassis. Its pretty ridiculous how loud this amp is. With the closed back 4x12 with EVs I can't seem to get it past 3 on the 60 watt mode without the bass shaking the foundation of my house. I've never played a triple rectifier but it'd be hard to imagine any mesa having bragging rights over this amp in the volume department.

I really need to get a 2x12 because theres no way I could lug that thing back and forth from gigs and practices without some roadies and a van (btw I'm not selling out any world tours anytime soon). This is my first half stack so I don't have much to compare to but maybe that cab is just a shitload heavier than most (could it just be the EV forces). On that boogie literature site it says it can get past 300 watts rms when its driven hard. So unless theres 2 speakers (which may end up sounding like crap) that could handle that I'm basically screwed.

 

[eldi]

Back in that era, Mesa made alot of those Mk amps on a custom order basis, and had a tendency to use whatever chassis they had on hand to build an amp, whether the printing on the panels were correct or not. My '85 Mk III has the "full power/half power" switch, which is how it operates if it was a 60/100 model, but its actually a simulclass model, so it is actually a "class A/simulclass" switch. That could also explain why you have that extra hole that is covered up in the back of the chassis.

I guess some folks would be annoyed by that, but I think that adds to the mystique & character of the older Boogie amps.

If you call Mesa & give them your s/n, they could probably tell you from their records if it was originally built with reverb or not. Their techs are very good about calling you back, & you might even get to talk to Mike B. himself!

On the coliseum amps, when the power switch is on "60" does it really power it down to 60 watts or does it actually work in half-power mode? Just out of curiosity..

 

[bloodspoint]

Yea I thought 2500 was a little absurd.

I took out the chassis today to get a good look at everything. Its got the usual "MD" written inside the chassis, and the tube slots are marked. The 4 preamps are positron 12ax7s. The 6 power tubes are Mesa 6l6s (yes the STR415s). Then theres a 6FQ7 tube (Does anyone know what this is?).

I think all the tubes are original or just really old replacements, but the guy who sold it said he hardly played it (which it looked like too). And I doubt he did too much damage to the 10,000+ hours the str415s can run.

Just how rare and valuable are these tubes? Should I take them out and hide them in a closet? Does anyone know if i can take out a pair of these and make the amp less wattage (theres 6 in it btw)? Then I'd at least have a couple spares.

That 6FQ7 could be your problem with the reverb right there. I don't think any Mesa amps use a 6FQ7, and if it's in a spot where a 12AX7 should be, well it's missing a triode. I'd try replacing that at the very least, and see if it doesn't fix it. i can't imagine what would have possessed someone to put that in there.

 

[JimAnsell]

That 6FQ7 could be your problem with the reverb right there. I don't think any Mesa amps use a 6FQ7, and if it's in a spot where a 12AX7 should be, well it's missing a triode. I'd try replacing that at the very least, and see if it doesn't fix it. i can't imagine what would have possessed someone to put that in there.

wrong.

my mark IIb coli has one too.
its written on the chassis as well.

 

[trem]

Isn't the 6FQ7 part of the limiter circuit?

 

[JimAnsell]

Isn't the 6FQ7 part of the limiter circuit?

no.

 

[trem]

Care to elaborate about what the 6FQ7 does Jim? Thanks.

 

[merendina]

The 6FQ7 is the phase inverter/driver tube along with the 12AT7 that acts as a buffer.

 

[Harry the Horder]

Ref that 6FQ7 it should be V6 and is for the Phase Inverter/Driver
Sorry I should have turned the page! never mind that confirms it more.

 

[trem]

Thanks Merendina and Harry. Hard to imagine without looking at the schematics though. I still don't get how the 2 tubes are used as phase splitter in a 6 tubes simul arrangement.