Mark III Black Stripe Gain Mods

[gepetto33]

Hello again!

Haven't had much luck with tech questions around here lately, but figured i'd try again with a different topic. I have an older Mark III Black Dot that i've done some of the basic "+" mods to - C27, C30, added bias pot, etc.... but alas, it's left me wanting a bit more. From the getgo this thing has never had enough gain for me, especially when compared to the Blue Stripe i purchased/sold to my ex-bandmate (i still kick myself for not keeping that one).

I realize that the easiest remedy for this would be to just buy a blue stripe.... but alas, my funds are tight right now, and i'd like to get this one sounding better if possible. I've gotten to be pretty familiar with this circuit, and am an adept enough (albeit not an "expert") technician to get in there an make some changes, so........ would anyone have some thoughts/suggestions to boost the gain in this amp a little? Something a little closer to the blue stripe, possibly? I know they're not 'night and day' differences between the two versions, so hopefully a couple tweaks could be done to get some more push out of this thing. Any input or suggestions would be much appreciated, cheers!!!!

Another thing to note is that i'm well aware of how a boost pedal/tube screamer works, and that my focus is specifically to increase the gain available within the lead channel. I have plenty of pedals that do different things to my sound, and this is a change i want from the amp itself. Anything closer to the blue stripe would be a step in the right direction. Thanks!

 

[Markedman]

I have owned blue and black stripe Mark lll amps at the same time and have posted videos comparing the two. All Mark amps need the right 12ax7 in V1 to sound great. A tube might sound good in one amp and fizzle in another amp, you have to do the changing yourself to hear the difference. Just because someone will say, "I use this NOS tube in all amps" isn't proof it will sound good in your amp. When the right tube is in your amp, you'll know, with me I was literally startled when I finally got the tone and gain I was looking for when I put a RCA with orange writing on it in my blue stripe. Talk about night and day in volume and gain, wow, it scared me, unreal! My black stripe came alive with an amperex bogle boy but it didn't respond well to the RCA and vice-versa.

 

[gepetto33]

I have owned blue and black stripe Mark lll amps at the same time and have posted videos comparing the two. All Mark amps need the right 12ax7 in V1 to sound great. A tube might sound good in one amp and fizzle in another amp, you have to do the changing yourself to hear the difference. Just because someone will say, "I use this NOS tube in all amps" isn't proof it will sound good in your amp. When the right tube is in your amp, you'll know, with me I was literally startled when I finally got the tone and gain I was looking for when I put a RCA with orange writing on it in my blue stripe. Talk about night and day in volume and gain, wow, it scared me, unreal! My black stripe came alive with an amperex bogle boy but it didn't respond well to the RCA and vice-versa.

You're certainly right about the importance of the V1 in terms of tone, and I've rolled plenty of tubes through both amps. Unfortunately this is more of an overall gain issue, and not as easy as just finding a hotter tube. Cutting gain has much more of a range with tube changing, since their gain rating varies between 20-100. When you're already at 12ax7 (100) then there's not much more room to go up, unfortunately.

 

[fretout]

I'd also have to say that the lack of gain is most likely due to a preamp tube in V1, or maybe even V3...but most likely V1.

If I compare my Blue Stripes to my No Stripe III+, the Blue Stripe definitely has more gain, but I would never describe the III+ as needing more gain, so I would guess that it's a preamp tube issue.

If you've rolled tubes through V1 and V3 with no results, maybe some gut shots would allow us to see what's going on...

 

[chipaudette]

Have you confirmed that the amp is running correctly?

For example, have you confirmed that the voltages at the anode pins of the pre-amp tubes is correct? We're looking for gross problems here...like 100V off, not a mere handful of volts. If the power supply is crapping out and you find that the tubes are running a hundred volts too low, it won't sound right.

Similarly, have you confirmed that the pull-shift on the Treble knob is working? If it's not, the lead channel definitely won't have enough "thrust". Switch to the lead channel, set the Treble to 7-8, and pull-push the treble knob back and forth. Is it definitely working? If it's a weak change, the LDR/relay might be dying.

Similarly, there's another LDR/relay at the end of the lead circuit to bring the lead signal back into the main signal path. If it's weak, you might be missing some gain. That one's harder to check, but if you know what I'm talking about, you might see a good way to probe its resistance without killing yourself.

Then, you said that you've swapped tubes, so worn out tubes shouldn't be an issue...but I've had brand new "known good" tubes prove to be not good once put into my amp. Very frustrating, but it does happen. So, I'd consider swapping in yet another set of tubes.

While you're swapping tubes (again), make sure that all the relevant tubes are 12AX7. Putting a 12AT7 in there by accident will definitely kill your gain. Also, look at the pins on the tube once you've pulled them out...a bent pin on a tube would be bad. Probably, the tube with the bent pin wouldn't work at all (which would be totally obvious), but you never know what might happen.

Good luck!

Chip

 

[gepetto33]

Thank you guys so much for replying... this is some good information. The tubes have definitely been rolled, and are all in strong working condition. Nothing is underpowered with 12AT7, 5751, etc.

I've checked voltage on the plates for both sides of V1 and V3, to which they check out fine. They read a little higher than the schematic notes, which is good by me. I was comparing mine to a blue stripe moreso than I was saying "there's something wrong with the gain". Meaning in comparison to the blue revision this one has LESS gain. Having found a user submitted schematic and reading the higher plate voltages on those versions - It makes a lot of sense now WHY my amp has less gain. Just compare the original schematic with the blue/red stripes listed on here and you'll see what I mean. I have readings on these for comparison, but they're not with me at this moment.

Having made this conclusion, I wanted to post an update saying I've done some of my own intuitive tweaks to the circuit and achieved what I needed to. I tried a few different things, and didn't end up going with straight up identical values to the red/blue stripe, but more of a hybrid between the two - keeping what I liked about my version, but just a little hotter on the gain tap. Let me know if you wanna know more about them, and i'll take some readings. Thanks again!

 

[fretout]

Meaning in comparison to the blue revision this one has LESS gain. Having found a user submitted schematic and reading the higher plate voltages on those versions - It makes a lot of sense now WHY my amp has less gain. Just compare the original schematic with the blue/red stripes listed on here and you'll see what I mean.

Well, yeah, the red stripes don't have as much gain as these crazy Blue Stripes, but for that matter, no Mesa before or since has had as much gain as a Blue Stripe. Even a No Stripe Coliseum (that used to belong to chipaudette, and had the III+ mod) can't compete with a Blue Stripe Coliseum's gain. But, with that said, Red Stripes are mean amps and just because they don't have as much gain as a Blue Stripe, they still have great gain available. I was originally trying to score a Red Stripe before discovering a Blue Stripe. I've played many, many Red Stripes, but I fell for the Blue Stripe.

If the Red Stripe seems anemic, then that would qualify as a problem, but if it's just a matter of getting the Red Stripe to sound like a Blue Stripe, you'll need a mod called "the C30 mod". The blue stripe has no cap on C30, while a Red Stripe has a 1000pf. Also, IIRC, the Blue Stripe has a 120pf across the grid and cathode of V2b to make its voicing like a Mark IIC+.

Can you expand on what mod you did? If you "split the difference", did you throw a 500pf cap in C30? If so, that's the same as the Black Stripes and the Purple Stripes.

 

[chipaudette]

Even a No Stripe Coliseum (that used to belong to chipaudette, and had the III+ mod) can't compete with a Blue Stripe Coliseum's gain.

Man, I wish had been an owner of a No-Stripe Coliseum...but that wasn't me. While I knew that a Coliseum's power could cause earthquakes in near-by continents, I didn't know that it was powerful enough to erase memories. Wow, that's some ooomph!

Chip

 

[fretout]

Even a No Stripe Coliseum (that used to belong to chipaudette, and had the III+ mod) can't compete with a Blue Stripe Coliseum's gain.

Man, I wish had been an owner of a No-Stripe Coliseum...but that wasn't me. While I knew that a Coliseum's power could cause earthquakes in near-by continents, I didn't know that it was powerful enough to erase memories. Wow, that's some ooomph!

Chip

I'll double check, but about a year ago, this amp was traded into Guitar Center as a "Mark IIC+", but it's actually a Mark III Coliseum. It used to belong to a fellow forumite who goes by "oneaussie", and then at some point wound up in your amp collection for a brief period of time before it was traded in at a GC in Commack, NY.

I'm pretty sure I saved the threads, so I'll post them up if I can locate them. It's very possible I could be mistaken, but I thought this was traded in and then you picked up a Suhr...

 

[chipaudette]

I'm pretty sure I saved the threads, so I'll post them up if I can locate them. It's very possible I could be mistaken, but I thought this was traded in and then you picked up a Suhr...

I've never had a Suhr either. Maybe someone is masquerading as me...and has a wicked amp collection. Lucky duck!

Chip

 

[fretout]

I'm pretty sure I saved the threads, so I'll post them up if I can locate them. It's very possible I could be mistaken, but I thought this was traded in and then you picked up a Suhr...

I've never had a Suhr either. Maybe someone is masquerading as me...and has a wicked amp collection. Lucky duck!

Chip

Edit: Sorry Chip, it was another user on a different forum that also goes by "chip" and had some very similar amps as some of the ones you've posted about. My apologies. Blame it on posting late at night!

 

[gepetto33]

Hello again!

I have an older Mark III Black Dot that i've done some of the basic "+" mods to - C27, C30, added bias pot...

Well, yeah, the red stripes don't have as much gain as these crazy Blue Stripes, but for that matter, no Mesa before or since has had as much gain as a Blue Stripe. Even a No Stripe Coliseum (that used to belong to chipaudette, and had the III+ mod) can't compete with a Blue Stripe Coliseum's gain. But, with that said, Red Stripes are mean amps and just because they don't have as much gain as a Blue Stripe, they still have great gain available. I was originally trying to score a Red Stripe before discovering a Blue Stripe. I've played many, many Red Stripes, but I fell for the Blue Stripe.

I think you came in a little late on this thread - my main posting mentions me having a Black Stripe, not a Red. If i had a red stripe there would be no reason for this thread, unless something was actually wrong with it.

"Splitting the difference" was in regard to the mods i did - at first i was trying to 'match' the blue stripe, via comparing schematics, but ended up deviating back towards the middle a bit. I listened to the amp after each change, and would restore a section back if it wasn't a pleasant change, thus gradually finding what sounded best. What i ended up doing was matching the plate voltage/gain on the V1b to that of the Blue Stripe. Basically what this did was keep the amp nice and raw sounding, but with a touch more push going into the lead channel…. because as we all know, the first volume knob is what sets up everything else down the line - R2, Lead, etc.