Mark IIB Loss of Gain after recap

[McBarry]

Sorry to hear about the continued woes..

All ideas will be guesses at best.. and plain conjecture at worst..
Careful examination and diagnosis is needed.

Sounds like subtle forces are at play but U seem convinced at the anomalies and as such, if your ears detect it then a multimeter and/or CRO should be able to verify.

let us know the eventual culprit(s).. regs, DB

 

[BlackBoxy]

hi, i know new PS caps can makes the amp sounds thin improving headroom especially drive lead chanel, it will need 100h to burn in to get back lovely fat sustain tones!

i would sugest you to let your amp on along the day for a week (you turn it off on the evening), as i did on my Mark IV to get back the magic boogie tone !

get in back the old tubes too , if it doesn't have any microphonics!

I have re-capped hundreds of amps and never found this to be the case,in a Boogie or any other brand amp.Any time I've re-capped an amp the improvement was instant,nothing to "burn in".Leaving an amp on all day everyday for a week is not good to do.

Hi, its not my feedback, i've done lot of re capping too , music amp and hifi , each time i've heard improving tone along hours played.

as fact the dialectric of electrolytics caps are forming chimicaly , crystal of aluminum under tension form the dialectric,crystal gets thiner along the days under voltage, making it lower on esr and sharper on filtering ripples while break-in time ! its not the case on film cap (who are formed when made) or resistors cable etc..
it is more effective on high quality (mil spec like) caps, as Mesa use into their PS amp, just weight a same specifications fashionable actual (general purpose cap for recapp) as F&t , atoms, IC etc.. and a Barker made for mesa to compare, it has almost half the weight , and after not really same tone thereafter in result!

diferencies between actual general purpose electrolytics is small, but when compared to mil spec quality, its not small!

its only my opinion

 

[MK IIB]

Guys I'm finding that the amp hasn't got a huge amount of top end.
I'm having to run the treble up around 9-10 to have any kind of clarity compared to say a Fender amp where the treble can be at around 6-7 and have plenty top end sparkle.
My SOB combo for example has loads more top end infact the tone controls on the SOB are a lot more effective and have a lot more tonal range.
On the SOB the treble can't really go above 6 or it's just too trebly!It also has a lot more bottom end too but the tone controls on the IIB don't have a lot of sweep at all?
Again I really don't know if there's something wrong with this IIB or if that's just the nature of the amp?
Also if I have the presence set to 0 it's as though there is a blanket over the amp even with the treble set at 9-10.
I find the presence rather harsh even at lower volumes and prefer the sound of the lead channel with the presence at 0 but the amp wont let me turn the presence to 0.It just sounds really muddy on the clean channel even with treble at 10!
I've got a feeling that the preamp/tone controls aren't acting exactly as they should but I'm not sure?
I've tried turning all tone controls down until there is no volume and the turning them up one by one and they do all work but they just don't seem like other Boogies where the tone controls have a massive range/effect?
The amp sounds warm but just not a lot of top end.I would have thought with the treble at 9-10 it would be just TOO much treble?
P.s should the pull treble shift only work on the lead channel?

 

[BlackBoxy]

Hi,

you question is rather difficult to answer , Fender's are in mind big headroom 3 pre stages amps , so lot voltage to sparkles here, Mesa are more marshally 5 stages pre , stucking headroom to control gain and overdrive !

to smooth you trebble , you could yank out harsh ceramic 750pf 250pf caps withing the tone stack and replace it with styroflex caps
http://www.hificollective.co.uk/catalog/polystrene-capacitors.html

it smooth nicely the trebley , making it creamy!

good luck

 

[MK IIB]

I wouldn't say the mark 2B is marshally at all it's far more like a Fender than a Marshall to me?
It's not that the amp is harsh it just doesn't have lots of treble on tap and tends to sound a bit muddy.
I don't like an overly trebley sound I'm just wondering if it's typical to have to run the treble so high on the 2B?Like full?
I'm curious to know if my tone controls are working/responding properly on the frequencies that they should and how I can determine this?
All tone controls do respond but don't have a lot of tonal sweep.
I don't know I just get a feeling there's something wrong as there doesn't seem to be a lot of range and from what I've read etc these amps can be "difficult to dial in" with a very minor turn of a knob affecting/changing the tone.Well this isn't the case here at all.
Hard to diagnose via the internet I know but apart from tubes what could cause these problems (if infact there is a problem)It would be great to be able to compare to another IIB.
Anyway the amp just doesn't feel "right" to me.
I also feel this is tied in to the lack of overdrive/sustain on the lead channel!
Also the preamp board seems to have been removed for some reason as there has been rubber rings glued to it and the chassis to secure it.I sent pictures to MESA and they said nothing looked out of place to them as far as wiring etc!
When recapped and serviced the amp was said to "OK"
It's very frustrating!I feel I'm constantly wrestling with it.

 

[BlackBoxy]

Hi,

you question is rather difficult to answer , Fender's are in mind big headroom 3 pre stages amps , so lot voltage to sparkles here, Mesa are more marshally 5 stages pre , stucking headroom to control gain and overdrive !

to smooth you trebble , you could yank out harsh ceramic 750pf 250pf caps withing the tone stack and replace it with styroflex caps
http://www.hificollective.co.uk/catalog/polystrene-capacitors.html

it smooth nicely the trebley , making it creamy!

good luck

I wouldn't say the mark 2B is marshally at all it's far more like a Fender than a Marshall to me?
It's not that the amp is harsh but rather doesn't have lots of treble on tap.I don't like an overly trebley sound but I'm just wondering if it's typical to have to run the treble so high on the 2B?Like full?
I'm just curious to know if my tone controls are working properly on the frequencies that they should and how I can determine this and if they are not what could be the problem?
Also the preamp board seems to have been removed for some reason as there has been rubber rings glued to it and the chassis to secure it but I sent pictures to MESA and they said nothing looked out of the ordinary to them as far as wiring etc!
As I said they do all respond but I don't know I just get a feeling there's something wrong as there doesn't seem to be a lot of range and from what I've read etc these amps can be "difficult to dial in" with a very minor turn of a knob affecting/changing the tone.Well this isn't the case here at all.Hard to diagnose via the internet I know but how can I find out if the tone controls are functioning as they should?
I also feel this is tied in to the lack of overdrive/sustain on the lead channel!
When recapped and serviced it was said to "OK"

marshally as structural pre stages, no tonaly!


http://www.classictubeamps.com/schematics/Mesa/Mesa%20Boogie%20MKIIB%20schematic.pdf
for more gain, there is a voltage divider on pin 2 of V2a , 2.2M resistor and a 470k resistor , on the Mark IIc+ or Mark IV , mesa use 3.3m /680k divider witch is in the same divider ratio as IIb, replacing 470k with a 680k would increase gain without being mushy, could experiment with 1Mohms . be shure to use 1/2W resistor , Good luck