Mark IIB.All original?(Help needed please)

[MK IIB]

Hi folks.I've just "inherited" a MK 2B.It's been in it's flight case for years.It's not sounding too great.There is also a low buzzing sound whenever a note is played.Sometimes it's an octave lower of the same note,or a note in between creating a chord?It's not tube related and it's present at very low volumes too!There is no buzzing or anything coming from the amp itself when no guitar is plugged in!
I know there has been some work done to this amp over the years and it is my mission to get it returned to it's stock/ former glory.I would really appreciate if anyone could take a look at the gut shots and see if there is anything that jumps out that would need fixed/replacing?Ie bad caps etc?I would also really appreciate if anyone can point out anything at all that has been changed?
Any help is much appreciated.
Thank you.

 

[MK IIB]

Can anyone offer any opinions on this please?

 

[b00g13mk2B]

First, find a good amp tech if you don't know how to fix things yourself (safety statement). That said, here is what I can offer from the pics you posted -

1) Sounds like a power supply problem or capacitor problem. Or even tubes. Item 5 may be the simplest check you can do.

2) Needs a good cleaning. The debris over the big blue electrolytic caps and everywhere. Can't tell if that is from some degrading foam inside, some part that overheated in the past or dust. Some chance that cleaning with the right electronics cleaner would help.

3) The regulator board looks like it was repaired. There are two power resistors on it that are big rectangles, not appearing to be stock.

4) Can't tell if the big blue capacitors on the regulator board are original or replacements. If original, they could be about to dry out. If replacement, depends on how old they are and if any other things happened to stress them. There are also smaller bypass electrolytic capacitors on the preamp board, that could have gone bad. Not everyone changes them when the filter caps are changed.

5) The screen resistors on the power tube board don't look like stock ones. The power tube sockets look like they got too hot once, another reason to suspect the screen resistors are not original.

6) Are the tubes you have old? If none of them glow bright red, then perhaps the are just worn out, especially the power tubes. Try replacements. A very bright tube could mean a bad tube or some other circuit issue that would stress new tubes.

Hope that helps.

 

[MK IIB]

Hi.Thanks you for your reply.
The amp will be going to a tech as I certainly don't have the know how on what to do.I really just wanted opinions as to anything that wasn't stock and had been changed.I am now sure the buzzing problem is the actual speaker itself.
Do you know if the PT is original?
Yes it definitely needs a good clean out.It's just dust on the electrolytic caps.
I tried other tubes but still isn't sounding great.No tubes glowing!
It's going to a tech anyway.If anyone spots anything else that they know to definitely NOT be stock I would really appreciate the info.
Thanks folks.

 

[b00g13mk2B]

I can't say about the transformer, don't have pics of mine and it is not nearby at the moment to look. Maybe a search of the forum can yield some information. Some Fender transformers could retrofit. If the mounting holes on the current transformer match the chassis, there are no extra holes, a good sign it is original. The tech should check the voltages anyway.

Can you tell if the speaker is an EVM12L? Or a Boogie version Black Shadow? Worth getting reconed. If something else, lots of people like the C90 new Boogie speaker of the newest Filmore. Speakers are very subjective, of course. Just get enough power rating and see what you like.

These amps are pretty rugged, your tech should be able to get it in good shape for the next few decades.

 

[MK IIB]

I can't say about the transformer, don't have pics of mine and it is not nearby at the moment to look. Maybe a search of the forum can yield some information. Some Fender transformers could retrofit. If the mounting holes on the current transformer match the chassis, there are no extra holes, a good sign it is original. The tech should check the voltages anyway.

Can you tell if the speaker is an EVM12L? Or a Boogie version Black Shadow? Worth getting reconed. If something else, lots of people like the C90 new Boogie speaker of the newest Filmore. Speakers are very subjective, of course. Just get enough power rating and see what you like.

These amps are pretty rugged, your tech should be able to get it in good shape for the next few decades.

The current damaged speaker isn't the stock speaker.It's a JBL 2130 which is a PA speaker so not worth having it repaired I don't think?
I'll have to get a speaker for this 2B.I think the speaker it came stock with was the MS-12?If I want it stock that's what I'll need to get but I've heard the EVM12-L are the best speakers for the mark series amps?
Do you know how the C90's compare to the MS-12's?
Thanks.

 

[b00g13mk2B]

Not sure, some say the 2130 is a "professional" version of the K120 JBL speaker. Maybe a good recone service could advise. If so, would be worth getting repaired.

I have not played a Boogie with an EVM12L or C90, can't tell you how they compare. Both are supposed to be fine speakers. Down side for the EVM is weight, very heavy. The MS-12 was a sort of copy of the EVM, made by Eminence. I have one in my MKIIA, bought it as a replacement years ago. It is a good speaker, get one if you are seeking originality. People seem to say the EVM12L is the best sounding between the two.

Mesa has a new Filmore series, call them and see which one they recommend. I would try one of these if I was buying a new speaker. There is a KS-100 used in the King Snake, and a KS-75 used in a few other amps. They are not listed specifically on the Mesa Store. Call and ask about availability.

Are you used to playing at loud volumes? All of these speakers have a different response as the input power goes up. My MS-12 Black Shadown is OK but not particularly lively at bedroom levels. Comes to life as the volume goes up.

 

[MK IIB]

Apparently the only thing that has been changed in this amp is pin 6 V1 and the pin 4 screen resistors on the power tube sockets?I thought the filter caps may have been replaced too as they aren't marked Mesa?
I think they'll need to be replaced now though if they have never been replaced before?

 

[McBarry]

Hi,

the main filter caps are original from the cream coloured ends and I can see a slight bulge in one - they've served their time so must be replaced.
Agreed, the screen and PSU dropper resistors are not original.
Tranny's all look original, and Mesa usually wedge a small piece of timber between the choke and main power tranny - can't see it due to pics angle.
One of the tiny treble caps near V1 looks sitting very high and looks not siliconed to it's partner - not how Mesa used to install them and may be a replacement.
There's a new pot on the PS board - most likely a bias setting pot - the Mk IIA actually had one installed from the factory - a blue cermet from my dim memory... This was discontinued in the IIB. Check yr serial number, although the IIA usually has an RP-6A preamp PCB and yours is an SP9A (very IIB era, although both my IIB's have RP9A PCB's - sorry, I don't know the difference for the SP series boards).
There's a new resistor V2 pin 7.
The lead drive pot shielded cable is usually routed UNDER the earth strap on that pot's pull switch - yours is free-running.
Relay, cathode caps and most other parts look original, and the lead dressing and general layout looks typical for a MkIIB.

But dude... that grime.... OMG... U could be your tech's bestest friend in the whole wide world by doing a bucketload of cleaning..

and I'd almost guarantee some tone will return as all manner of stray little voltages and signal loss will happen courtesy of that crud almost jumpering between tracks..

Good luck with it.. it's certainly "lived" and as such, I'll bet has a mountain of tone just waiting to escape...
Dave

 

[MK IIB]

Hi,

the main filter caps are original from the cream coloured ends and I can see a slight bulge in one - they've served their time so must be replaced.
Agreed, the screen and PSU dropper resistors are not original.
Tranny's all look original, and Mesa usually wedge a small piece of timber between the choke and main power tranny - can't see it due to pics angle.
One of the tiny treble caps near V1 looks sitting very high and looks not siliconed to it's partner - not how Mesa used to install them and may be a replacement.
There's a new pot on the PS board - most likely a bias setting pot - the Mk IIA actually had one installed from the factory - a blue cermet from my dim memory... This was discontinued in the IIB. Check yr serial number, although the IIA usually has an RP-6A preamp PCB and yours is an SP9A (very IIB era, although both my IIB's have RP9A PCB's - sorry, I don't know the difference for the SP series boards).
There's a new resistor V2 pin 7.
The lead drive pot shielded cable is usually routed UNDER the earth strap on that pot's pull switch - yours is free-running.
Relay, cathode caps and most other parts look original, and the lead dressing and general layout looks typical for a MkIIB.

But dude... that grime.... OMG... U could be your tech's bestest friend in the whole wide world by doing a bucketload of cleaning..

and I'd almost guarantee some tone will return as all manner of stray little voltages and signal loss will happen courtesy of that crud almost jumpering between tracks..

Good luck with it.. it's certainly "lived" and as such, I'll bet has a mountain of tone just waiting to escape...
Dave

Thank you very much for your help Dave.The previous owner(My pal)did say his old tech had installed a bias pot.Should I have this removed?I do want it returned to stock but is this mod beneficial to the amp?
He was also under the impression that one of the transformers had been replaced which is why I thought it could have been the PT but he could have been mistaken?
I'm taking the amp to a tech who knows his 2B's so hopefully he can work some "magic" on it.
Dave should I have the replaced parts replaced again to bring it back to stock or are they suitable replacements?
It actually blew a fuse the other day but I think it was due to the old power tubes as I noticed one of them had the middle big plastic pin broken and the glass was exposed.
With regards to the cleaning,I would be really scared in case I did any damage to the amp.I will pay the guy extra for giving it a good clean out.What would you use to clean the amp anyway?
Once again thanks for your help.I can't wait to have this fixed up and sounding like it used to.
All the best.

 

[McBarry]

Hi,
most of yr queries are up to personal preference and I'm sure your tech will be able to advise and both or U work out an agreeable plan..

For cleaning, I use methylated spirits and q-tips (cotton-tipped ear cleaners), tiny paint brushes and small cloth rags.. Rarely anything more aggressve, and def not acid-based circuit board cleaner.
Go gently - you won't bend/hurt/break anything if U are gentle.
Blowing fuses could be serious or simply a 34 year old fuse having had enough...

It def sounds tech-time though..

DB

 

[MK IIB]

Hi guys.
Could someone please tell me what's the deal with this PT?Is it leaking?As far as I know power transformers don't leak as such but this doesn't look like the varnish/sealant.More like bubbles from overheating?
Any info would be appreciated.

 

[McBarry]

U are correct, it likely being lacquer.
I don't know the exact product used in the mfgr of these trannies, but conventional and historic mfgr process is to wind the tranny, then dip in a bath/pot of lacquer and drain for a bit and then into an oven to bake.
One of aims of this process is for the lacquer to help stop vibration between the prim/secondary windings - it replaces air between windings and when dry it helps keep the windings/laminations a set distance apart.

 

[MK IIB]

U are correct, it likely being lacquer.
I don't know the exact product used in the mfgr of these trannies, but conventional and historic mfgr process is to wind the tranny, then dip in a bath/pot of lacquer and drain for a bit and then into an oven to bake.
One of aims of this process is for the lacquer to help stop vibration between the prim/secondary windings - it replaces air between windings and when dry it helps keep the windings/laminations a set distance apart.

I've not seen another that looks as bad as this!Infact I've not seen another Mark amp that looks as bad as this one does inside.It was gigging 7 days a week from 1981-1989 though and a lot from 1990-99

 

[McBarry]

EIGHT solid years of gigging, then a brief reprieve, then another NINE solid years gigging...
C'Mon, are U really that surprised at the worn and dusty insides??

Re tranny lacquer - I've seen some that you'd swear were painted AFTER the baking.. a couple of Fender Bassman amps come to mind.

I'm my own tribe of Boogies they've all got varying degrees of lacquer droplet formation. No biggie..
I view it as a good thing. Plenty lacquer hopefully means plenty inside too.

As long as the trannies are not humming too much then all is well.
If they are humming abnormally loudly, get yr techs' opinion on re-potting or further repair suggestions.

 

[MK IIB]

Thank you for your insight Dave.I appreciate it.Yeah it's certainly worked hard this amp.

 

[MK IIB]

Hi Guys.I need some small parts for my mark IIB.
I need 4 of the screws for the top of the amp where the chassis is screwed into to the cabinet.Does anyone know what size these should be and if there are original replacements to be had?
I also need 4 of the screws/small washers for the front pannel of the amp as there is only one on it and it doesn't tighten.
If anyone could tell me what size these screws should be I'd appreciate it?
Another thing, the pre amp board is being held in place with some kind of rubber rings?How should the board be secured to the chassis?I'm wondering if the pre amp board has sustained some damage at some point as 3 of the pre amp tube sockets have some kind of thermal paste to hold them in place?
Any help is much appreciated.
P.s I've added some pics to show what I mean.

 

[McBarry]

G'day... (again..!!)
the preamp rings U see are not original.
Those Rp series boards were held in with double-sided foam, about 1/2" thick.. hard to believe...
The PSU boards had 3 plastic stand-offs - 2 near the preamp board end and one screw between the 220uf caps.
Screws- the Sus-4 system (screws recessed in the cabinet top) and "standard" screwing into the chassis system screws are still avail.
4 screws/washers front panel?? there's no screw on the face panel.
Maybe it's the speaker/grill screws you mean, and cup washers?
They used a strange thread, but they're close to #8 size - sorry dunno the imperial correlation. Cup washers - I've used #8 size.
Hope this helps, Dave

 

[MK IIB]

Hi Dave,Just seen your reply.
Yeah I didn't think those rings holding the preamp board to the chassis were original.God knows what was used to hold them in place?It looks really gunky/sticky?
I definitely want these removed and something more "original" put in place.
Yes regarding the front pannel screws/cup washers,I need 4 of each and 4 of the top screws that screw into the chassis from the amp top.
My aim is to get together all the parts I need for this IIB to be restored to stock and just go "here ya go" to the tech to perform the work needing done.
Just trying to source the correct parts.
I got an SOB combo really just for the MS-12 speaker for the IIB and to use other parts for my IIB but having played/gigged with it and heard how good it can sound,I can't bare the thought of breaking it up just for parts!
Thanks a bunch.

 

[McBarry]

They used thick strips of about .5" wide double-sided foam to hold the PCB's in place.
Strong, didn't get heat affected.. PITA to work with though..The screws and mounting screws will be easily avail from MB..

It'd be pretty sad to cannibalise the SOB combo for a couple of easily-obtained parts..

Consider someone out there might really love an SOB and would be gracious to purchase yours..

Good luck with it, it'll be a blast when it's done !!

Keep us informed too - years from now folks read these threads and glean tons useful info..!!

DB