Mysterious Mesa amp(s) problem, I'd appreciate some help

[Beedster]

5 minutes ago, spyder said:

The valve with the white top is faulty.

There is an air leak.

From the web......

 

White getter on a bad tube VS a healthy tube getter

The second thing to look for is the condition of the getter. This is the greyish coating usually found at the top of a tube, but can be on the sides, or both top and sides, depending upon the tube type. Any color from grey/silver, to black is healthy. When a vacuum tube develops an air leak (a small crack or bad seal by a pin for example) this getter color will change to pure white. 

 

Hope this helps.

Thanks @spyder that’s much appreciated and helpful. I’ve a lot of tubes here that will be my first port of call for sure, Russ do you have any spares?

[Shaggy]

This may be no help at all, but a few years ago I had a similar issue with my MB Walkabout (also M-pulse).

After much fiddling as tried above which didn’t seem to help, it seemed to work fine if I switched power on with the preamp gain and master volume set at zero, and active tone controls turned all the way down.    Leave it to warm up for around a minute, before turning up controls to working levels.    No idea why it worked, but it’s what I’ve done ever since.

 

Good luck, and if unable to sort I’d certainly take it to a decent amp tech before trying Mesa.

[sandy_r]

33 minutes ago, spyder said:

The valve with the white top is faulty.

There is an air leak.

From the web......

 

White getter on a bad tube VS a healthy tube getter

The second thing to look for is the condition of the getter. This is the greyish coating usually found at the top of a tube, but can be on the sides, or both top and sides, depending upon the tube type. Any color from grey/silver, to black is healthy. When a vacuum tube develops an air leak (a small crack or bad seal by a pin for example) this getter color will change to pure white. 

 

Hope this helps.

 

Should be easy to confirm then, 'cause that valve is the driver to the Power Section and it is located after the Send/Receive Loop

 

So, whichever of you gents is going to do any follow-up checking, do the FX Loop A/B test suggested above (2 Amps, 1st as Pre, 2nd as Power) to confirm which half is faulty then switch off, let cool, and swap the 2 valves (which are the same type), repeat test - if the fault follows the valve, that confirms that valve has failed and no other issue

 

[Steve Browning]

Now you mention it @rumblefish had a similar issue which turned out to be a pre-amp valve.

 

The valve needed to be of a certain spec. Do you recall Rob?

[sandy_r]

38 minutes ago, Steve Browning said:

The valve needed to be of a certain spec.

 

Both valves listed as 12AX7 (a standard valve ...but genuine parts preferred!) 🤔

 

Edited January 6 by sandy_r

[binky_bass]

@Beedster - sorry, no spare valves here unfortunately! Short of taking one out of the Big Block and chucking it in the M-Pulse. Though I'll be absolutely honest and say A: Taking the BB out of the Mesa case is an absolute pain and B: At this stage, my personal preference is to do a hand-back at a time convenient. 

[Beedster]

1 hour ago, binky_bass said:

@Beedster - sorry, no spare valves here unfortunately! Short of taking one out of the Big Block and chucking it in the M-Pulse. Though I'll be absolutely honest and say A: Taking the BB out of the Mesa case is an absolute pain and B: At this stage, my personal preference is to do a hand-back at a time convenient. 

Agreed Russ, I’ll sort the fix, looks pretty straight forward 👍

[Beedster]

Great help above all thank you so much, I’ll update once I’ve run the tests, swaps etc 👍

[agedhorse]

Almost certainly the valve with the white getter coating.

[Beedster]

On 06/01/2024 at 11:00, Shaggy said:

This may be no help at all, but a few years ago I had a similar issue with my MB Walkabout (also M-pulse).

After much fiddling as tried above which didn’t seem to help, it seemed to work fine if I switched power on with the preamp gain and master volume set at zero, and active tone controls turned all the way down.    Leave it to warm up for around a minute, before turning up controls to working levels.    No idea why it worked, but it’s what I’ve done ever since.

 

Good luck, and if unable to sort I’d certainly take it to a decent amp tech before trying Mesa.

 

That really made me smile Greg, so while it may not solve this particular problem, it still helped

 

I'm generally pretty good with these things so even if not the tube there's a 50/50 chance I'll get it sorted, if not there's a nice guy down the road who exerts magical powers over amplification. In both our cases powerful fiorces appear to be ensuring that we keep hold of our respective Mesa gear  

[Beedster]

20 hours ago, sandy_r said:

 

Both valves listed as 12AX7 (a standard valve ...but genuine parts preferred!) 🤔

 

Thanks @sandy_r, luckily I have a rather substantial collection of pre-amp (and power) tubes here so will have some fun experimenting. I'll update once done 👍

[Beedster]

4 hours ago, agedhorse said:

Almost certainly the valve with the white getter coating.

 

Many thanks @agedhorse, I hope so!

 

While you're here, as I mentioned above @Steve Browning was kind enough to send me - and at no cost - a foot-switch for an M-Pulse 600. Sadly the pin number of the cable differed to that on the rear of the amp itself so I was unable to use it. Is there a workaround for this or is it simply a case of that foot-switch will not work with that model of the M-Pulse?

 

Chris

[agedhorse]

Try the valve before screwing with anything else. 
 

I don’t recall if all M-Pulse models used the same foot switch or if there were differences. I will look to see if I can find the info, but don’t attempt to bodge something together because the switching system could be damaged by an incorrect connection. This was from an era when a lot of changes were happening to our entire switching protocols (including guitar amps).

[sandy_r]

19 hours ago, Beedster said:

...[Steve Browning] was kind enough to send me - and at no cost - a foot-switch for an M-Pulse 600. Sadly the pin number of the cable differed to that on the rear of the amp itself so I was unable to use it. Is there a workaround for this or is it simply a case of that foot-switch will not work with that model of the M-Pulse?

...

 

If it helps towards answering your peripheral question, Chris, the Mar 2001 schematics for both the 360 & 600 M-Pulses employ the same 5-pin 180-degree DIN connection for the footswitch (the 5 wires give Gnd + switching for Masters, Loop, Compr & EQ)

 

 

(each switching path is a passive circuit of switch, resistor and LED in series to Gnd, protected on the Amp side by opto-isolating chips)

 

Edited January 8 by sandy_r

[Beedster]

18 minutes ago, sandy_r said:

 

If it helps towards answering your peripheral question, Chris, the Mar 2001 schematics for both the 360 & 600 M-Pulses employ the same 5-pin 180-degree DIN connection for the footswitch (the 5 wires give Gnd + switching for Masters, Loop, Compr & EQ)

 

 

(each switching path is a passive circuit of switch, resistor and LED in series to Gnd, protected on the Amp side by opto-isolating chips)

 

 

Hi @sandy_r, looking at sopme of your posts (the Realist for example), I'm not sure how this forum manages without you! Many thanks, I'll check this out when I get the M-Pulse back later this week 👍

[sandy_r]

8 minutes ago, Beedster said:

 

Hi @sandy_r, looking at sopme of your posts (the Realist for example), I'm not sure how this forum manages without you! Many thanks, I'll check this out when I get the M-Pulse back later this week 👍

 

thanks for the kind words, Chris, i'm just a small cog on a big wheel of experience on this site - it's great that we're all able to share something, across so many topics, bass-related or otherwise. i've learnt so much in my few months here - and had a lot of fun, too !

 

hope you folks manage to get the M-pulse sorted and back er, ...on the road again

 

[agedhorse]

On 06/01/2024 at 00:38, Beedster said:

Thanks for your help @sandy_r and @Downunderwonder. Quick answer to some of the above; as far as I know I haven't used monster cables, and despite @Steve Browning very very kindly sending me a Mesa footswitch a while back I was never able to use it as apparently there were two version of the M-Pulse (I meant to open a thread here asking whether the cables could be switched but for some reason never got around to it). I think examining toggle positions might be helpful if Russ has the time and patience to do so, if not I'll continue this once I've collected the rig 👍

 

I have a strong sense that something I was doing here has led to these problems with the two previously trouble-free units, although much like the final scene of Burn After Reading (which if you've not see you really should), I'm damned if I know what the hell it was 🤔 

 

Thanks again folks 👍

Do the two foot switches say M-Pulse? Do they have the same number of pins on the DIN connector? 

[Beedster]

7 hours ago, agedhorse said:

Do the two foot switches say M-Pulse? Do they have the same number of pins on the DIN connector? 

 

Hi @agedhorse, I'll check re the switches saying 'M-Pulse', although IIRC it does (I have only the one), but the pin numbers certainly differed between the unit/cable and the amp itself hence my inability ti use it 👍

[Beedster]

Hi @agedhorse, photos below

 

 

 

 

 

 

 

 

[sandy_r]

1 hour ago, Beedster said:

 

 

 

Thats a B-Link 1A - 5 switches (adding Tuner Mute) - your amp version only supports 4 switches (The B-Link F/S)

 

...if you, or a Techie friend, are confident with checking wire continuity and making a plug-type mod, you could swap out the existing 7-pin DIN on the cable (at the Mesa end) for the relevant 5-pin plug needed by your amp, and you'd be able to use the 4 switches as expected by your amp (Solo, Compression, Loop & EQ)

 

Or, you could make a complete new cable similarly (ie. 7-pin to 5-pin, 5-wire shielded cable?) and keep the original cable unmodded, in case you ever sell the footswitch on

(personally, i'd prefer this option)

 

Edited January 9 by sandy_r

[Minininjarob]

If you are anywhere near Huddersfield I have an Orange VT1000 valve tester you can pop the valves in. 
Sometimes if they test ok with a multimeter they still don’t work in situ. 
 

Edited January 9 by Minininjarob

[No lust in Jazz]

I had a Walkabout Head that used to cut out on a seemingly abstract basis, but if you hit the strings really hard, this could 'shock' it back to life.

 

Took it to a (very good) amp tech who couldn't find a fault, but he noted that the values of the components on the input circuit were an order of magnitude lower than another amplifier (Marshall) that he was working on. Long story short - I had him replace the components in the input stage of the WA and the issue was resolved.

[agedhorse]

9 hours ago, sandy_r said:

 

Thats a B-Link 1A - 5 switches (adding Tuner Mute) - your amp version only supports 4 switches (The B-Link F/S)

 

...if you, or a Techie friend, are confident with checking wire continuity and making a plug-type mod, you could swap out the existing 7-pin DIN on the cable (at the Mesa end) for the relevant 5-pin plug needed by your amp, and you'd be able to use the 4 switches as expected by your amp (Solo, Compression, Loop & EQ)

 

Or, you could make a complete new cable similarly (ie. 7-pin to 5-pin, 5-wire shielded cable?) and keep the original cable unmodded, in case you ever sell the footswitch on

(personally, i'd prefer this option)

 

Correct, this newer format was also used on some other bass products too (though not identical). There may have been other differences as well to the way the logic was handled. I don’t have the docs for the later one handy.
 

I would look for the correct footswitch rather than attempting to modify the 5 function one. 

[agedhorse]

4 hours ago, No lust in Jazz said:

I had a Walkabout Head that used to cut out on a seemingly abstract basis, but if you hit the strings really hard, this could 'shock' it back to life.

 

Took it to a (very good) amp tech who couldn't find a fault, but he noted that the values of the components on the input circuit were an order of magnitude lower than another amplifier (Marshall) that he was working on. Long story short - I had him replace the components in the input stage of the WA and the issue was resolved.

The values of the components had nothing to do with your problem, it’s not a Marshall amp. 
 

The fix was just a lucky byproduct of the “repair”.

[sandy_r]

46 minutes ago, agedhorse said:

I would look for the correct footswitch rather than attempting to modify the 5 function one. 

 

No suggestion above of modifying the 5 function footswitch 

 

a modified cable only needs to keep exactly the same wires as used to switch Solo, Compression, Loop, and Eq via a 5-pin DIN into the M-Pulse - the extra wires from the B-Link 1A can just be omitted (disconnected)

 

Edited January 9 by sandy_r