'80 Mark IIA

[Laurent Brondel]

I just got that one, pretty clean, 100w version with reverb, swapped the original EVM 12L for an Eminence CV-75 and yanked the modern tubes for some NOS ones.
Original electrolytics, they look fine and the amp is quiet, I may change them down the line though.

The clean channel sounds absolutely great, the reverb is surprisingly lush and quiet, but the lead channel has a lot less gain than either my MarkIII or SOB, even with all the knobs pulled (boost, treble shift & bright), and is kind of muddy and underwhelming.

I assume this is what it is, I don't intend to mod it really, but is that what it's supposed to be?

 

[MisterMojo]

Congrats! Great looking amp! IME, the cleans are primarily what the IIA is about. You can get some nice crunch out of it for late 70’s /early 80’s rock...but it is not a tight, high-gain amp as later versions moved towards. Enjoy... it’s a wonderful amp to have in your fold.

 

[skelt101]

Be careful not to overpower that speaker! At the 60 watt setting, you're probably okay for a while. However, "they" usually say to double the amp's wattage when selecting the power rating of a speaker. E.g. for a 100 watt amp, a 200 watt speaker is safe.

 

[woodbutcher65]

That thing should be a high gain monster. It should have as much gain as any Mark IIB. If it doesn't, something's wrong. Maybe it has really weak preamp tubes.

The capacitors are LONG overdue for replacement. Get that done quickly. I wouldn't play it until it was recapped.

Shame it has no EQ. The EQ MAKES a Mark II.

I had a Mark IIA HRG head. Serial 3116. If I ever find it I want to buy it back. It had as much gain and grind as any Metallica album up to the mid 80s.

 

[Laurent Brondel]

Be careful not to overpower that speaker! At the 60 watt setting, you're probably okay for a while. However, "they" usually say to double the amp's wattage when selecting the power rating of a speaker. E.g. for a 100 watt amp, a 200 watt speaker is safe.

Thanks, but to blow a 75w speaker you have to play much louder than I do here… No problem with the wattage, I use it as a clean platform in any case.

That thing should be a high gain monster. It should have as much gain as any Mark IIB. If it doesn't, something's wrong. Maybe it has really weak preamp tubes.

The capacitors are LONG overdue for replacement. Get that done quickly. I wouldn't play it until it was recapped.

Shame it has no EQ. The EQ MAKES a Mark II.

I had a Mark IIA HRG head. Serial 3116. If I ever find it I want to buy it back. It had as much gain and grind as any Metallica album up to the mid 80s.

From what I've read on this forum IIA owners have had the same experience with the gain channel on that amp. Was your modded or made to order a bit different?
In any case the filter caps are out of the audio circuit and all voltages seem OK, mine is pretty quiet and sounds great on the clean channel, but yes I plan to do a cap job, I am ordering the parts at CEDist today.
My amp came with brand new JJ preamp tubes and Sovtek 6L6WXT+, and actually those sound very good.
I swapped them for NOS RCA and EI for preamp and a quartet of JAN5881 for the power tubes, which sounds equally great, perhaps better.
Of note, no fetron on mine, but a 12ax7 in the tube slot, which sounds the same as v2 when I switch. No trace of any mod on the amp though.
Of note that amp runs a little cooler than my other Boogies, between 450 and 458v on the plates depending on power tubes, and the bias is a little hotter.

 

[woodbutcher65]

Order the capacitors from Mesa. They are currently using BMI caps and those are as good as you can get. Don't order the caps from anywhere else. There's no point. Mesa's price for those caps is probably lower than you'd pay for caps anywhere else that aren't as good.

It is totally untrue that the filter caps are out of the audio circuit. The entire amp is an audio circuit. The power supply is part of that circuit. Noise in the power supply is noise in the amp.

And if those caps should fail...and they're running on borrowed time...the penalty may be the destruction of a power transformer.

DO NOT RUN THE AMP UNTIL IT HAS BEEN RECAPPED. They're too old to be trusted. Take my advice and you'll never regret it. Ignore it, and you might.




My Mark IIA was a straight run stock order. No mods.