Mark III black dot head - any inputs?

Hi - I was planning on getting a used Mark V but the prices are still too high so I decided to try another one of the Mark series amps. I have a Lonestar classic 2x12 and a mini rec w/ a 2x12 rectifier cab and I hope this complements them well. I plan on using this with a 1x12 lonestar cab w/ a C90. The Mark III I just bought is a black dot head with eq, reverb and simul class and it will arrive later this week.

The serial number is 152XX. I have read a little about the transformers on here but not sure if this will have the 105 or not or if it really matters. Let me know what I should look for.

Any advice on anything I should check out on the amp right away to see if there are any problems would be appreciated. Unfortunately the amp doesn't come with any footswitches. I have a few foot switches for other amps I might try to see if they work.

Thanks for any feedback!

The PT would actually say 105-162XXX and is almost 4 inches thick in the laminations.
OT may be SC-152019B or 562003. Any shorting 1/4 inch footswitch will change modes/channels on the amp. You would need two for lead/clean and R2.

It has two inputs. one instrument and one preamp in / power amp out..... :mrgreen:

Thanks for the transformer info. It has the 105-162XXX and SC-152019B transformers.

So far I was able to walk through almost all of the features on the amp (the manual helped alot for initial settings, it was a little trickier than the mini and lonestar). So far I only spent time on the lead channel, fantastic! I was able to find a foot pedal that I could test everything except the Reverb/EQ. I really want to figure out how to get the eq foot switchable (probably the only thing I want to switch in and out). I have a 2 button marshall pedal but it didn't work. I noticed that the amp does pop pretty loudly when the the eq is switched, is this normal? I am used the channel switching pop on the mini so I guess this is sort of similar.

Looks like the amp has Winged C 6L6s and the pre amp tubes are a boogie SPAX7 in position 1 and Svetlana in the rest (never used Svetlana before). The power tubes on this amp are way hotter than my Lonestar or 6505. It feels like a heater! Does the Mark III generally run hotter than other amps?

I pulled out the chasis just to see what shape everything is in (ridiculously heavy) and I didn't see any bulging or blown capacitors. Not sure what else to look for to determine the condition, I took a few pictures so I could go back and look later.

When I first turned on the amp I didn't really notice the fan noise but now I noticed that it is pretty loud but not really an issue unless it stops working.

I played the Mark III the last three days since getting it and it has had a volume drop out each day after playing for a while (~1hr). The volume drops to an almost inaudible level for several minutes. One of the times I had to put it on standby and switch it back to get the volume to return. Today the volume just came back after several minutes (I did tap the power tubes though). The only thing I noticed with the power tubes was that one of them has the plate glowing red.

Any inputs on what might be causing the volume drop out would be greatly appreciated.

Plates glowing red are a warning sign that a power tube is on it's way out - when were they last changed?

I am not sure how much use these tubes have. I switched the outer and inner tubes and put it in class A and this doesn't help with the volume cutting in and out. I am pretty sure this isn't a power tube issue. When the volume does come back the tone isn't very good. I will try swapping out the pre-amp tubes as well.

When I got the amp it was really dirty and dusty inside. I did use some compressed air to see if it would help clear out any dust, dirt and debris but this also didn't help with the volume cut out / fade away.

After reading through all of the previous Mark III posts on this board (this board is an excellent source of info) I noticed alot of comments about the need to replace capacitors at some point and it sounds like it wouldn't be cheap. If this is the cause I will probably just return this amp for a refund. I think $830 was already on the high end for this amp (no footswitches, missing slider, alot of dust/dirt inside). Should I also expect this price to include tubes that aren't on the edge of failing? I still want a Mark series amp but maybe I will just look for another Mark III, IV or V. What do you think?

Hi Mjj,

bad to hear you have so early problems with your amp after buying.
If there's no income and special technical advices from other guys here in the next time to proceed them successfully, I advise you to send it to the "Mark-magician" Mr. Mike Bendinelli at MESA for servicing. After so a long time I think, there's a urgent need to do this, if the amp hasn't seen MESA or another skilled tech before.

Good Luck

megavoice - Thanks for the note.

I swapped out all of the preamp tubes to ensure they weren't the issue but still having the volume drop after playing for a while. If there are any experts on the schematic I would be interested to know what the difference is in components that are active when the effects loop is open vs. bypassed with a patch cable. Any capacitors in the effects loop that might be contributing? Any ideas on why this happens after ~1hr of playing (heat?)?