1987 Mark III Red Stripe DRG - Channel 2 and 3 Unwanted Noise

[quad48uF]

Before I send my Mark III off to the tech, anyone care to give me their input on this? Channel 1 is unaffected and the volume can be put to MAX without issue. It is only on channels 2 and 3 that there is a soft hum. Channel 3, if the Lead Master knob is turned passed 3 the hum becomes feedback almost like putting your guitar in front of the speaker cabinet under high gain. I did the tube test starting in V1 and the tap check. The power tubes were also replaced, to no affect.

 

[woodbutcher65]

You say it hums, but other than that, does it work? Or is there ONLY hum?

 

[quad48uF]

You say it hums, but other than that, does it work? Or is there ONLY hum?

The amps works as it should. The knobs can be turned and pulled and they function as normal. On channel 1 there is no hum and sounds like it should. When on Channel 2, a noticeable hum starts that gets louder as you turn up the volume. On channel 3, the hum gets slightly louder but when turning the lead master past 3 it goes from a dull hum to a sort of feedback. You can still play the amp but it's noisy as h***!

 

[quad48uF]

So here’s an update on my “red stripe”. I sent the amp into Mesa for service, Mike B. informed me it’s not a red stripe at all but a purple stripe. Won’t matter anyhow since it’s now a 3+, should be back any day! It got the full work up so I’m sure it was just old parts causing the hum from before.

From Mike;

#19548 MK LC chassis Amp is not RED dot, it’s purple. Finish Reverb Glitch update. Upgrade the .1/400 caps at V5 to .1/600 v. Upgrade a few preamp plate resisitors. Clean pots pulls jacks pre and pwr tube sockets contacts. Pre tubes are well. EQ sliders are well too.



The 6L6s are ?? One is no good, others are tired.

Do you want the electrolytic caps done ? Close to 40 years soon, kinda seems like a good idea at this point, that said they are still working fine at this time.

Would you like the front toggle switches replaced to match the stock EQ switch?

Might need to remove and rebuild some of the pull pots, 1st cleaning did not yield much results on the pull switches…. we will see after another cleaning.



The not a “red” dot has no effect on the outcome of the clean and lead sounds once the + is done so no worries there. The R2 master pot is not quite right, it will work better too.

The Gain of R2 is not as hot on the pre”red” versions, that’s all.



.

 

[Henz]

So here’s an update on my “red stripe”. I sent the amp into Mesa for service, Mike B. informed me it’s not a red stripe at all but a purple stripe. Won’t matter anyhow since it’s now a 3+, should be back any day! It got the full work up so I’m sure it was just old parts causing the hum from before.

From Mike;

#19548 MK LC chassis Amp is not RED dot, it’s purple. Finish Reverb Glitch update. Upgrade the .1/400 caps at V5 to .1/600 v. Upgrade a few preamp plate resisitors. Clean pots pulls jacks pre and pwr tube sockets contacts. Pre tubes are well. EQ sliders are well too.



The 6L6s are ?? One is no good, others are tired.

Do you want the electrolytic caps done ? Close to 40 years soon, kinda seems like a good idea at this point, that said they are still working fine at this time.

Would you like the front toggle switches replaced to match the stock EQ switch?

Might need to remove and rebuild some of the pull pots, 1st cleaning did not yield much results on the pull switches…. we will see after another cleaning.



The not a “red” dot has no effect on the outcome of the clean and lead sounds once the + is done so no worries there. The R2 master pot is not quite right, it will work better too.

The Gain of R2 is not as hot on the pre”red” versions, that’s all.



.

Great!! May I ask what the reverb issue was? Thanks. Jim

 

[quad48uF]

Great!! May I ask what the reverb issue was? Thanks. Jim

Next time Mike B emails me I will ask. Although, this may be part of the overhaul. I thought I saw the reverb glitch fix on an older thread as well

 

[Henz]

Next time Mike B emails me I will ask. Although, this may be part of the overhaul. I though I saw the reverb glitch fix on an older thread as well

Ty. Reason I ask is my C+ verb sounds kinda meh! Thin and harsh, if that makes sense.

 

[user 41014]

From Mike;

#19548 MK LC chassis Amp is not RED dot, it’s purple. Finish Reverb Glitch update. Upgrade the .1/400 caps at V5 to .1/600 v. Upgrade a few preamp plate resisitors. Clean pots pulls jacks pre and pwr tube sockets contacts. Pre tubes are well. EQ sliders are well too.

Please also ask him what the plate resistor upgrades were- higher wattage R's or changing the values for different gain structure?

 

[quad48uF]

Update Henz and Electric Mayhem! This is from the man himself!

"rev glitch lowers the voltage on rev drive stage in two places. we found early mk3s had an issue with rev being in the same tube for drive and return. That fixed it.

upgrade is just that, higher wattage if prudent and when I have seen parts that have failed repeatedly on a model, I always replace them, failed yet or not."

---

 

[user 41014]

Update Henz and Electric Mayhem! This is from the man himself!

"rev glitch lowers the voltage on rev drive stage in two places. we found early mk3s had an issue with rev being in the same tube for drive and return. That fixed it.

upgrade is just that, higher wattage if prudent and when I have seen parts that have failed repeatedly on a model, I always replace them, failed yet or not."

Thank you!

 

[Henz]

Update Henz and Electric Mayhem! This is from the man himself!

"rev glitch lowers the voltage on rev drive stage in two places. we found early mk3s had an issue with rev being in the same tube for drive and return. That fixed it.

upgrade is just that, higher wattage if prudent and when I have seen parts that have failed repeatedly on a model, I always replace them, failed yet or not."

---

Thank you. Sounds like he may have lowered the verb plate resistors values.

 

[quad48uF]

The Mark III has been home for about a week now and man, this thing is killer. It is now a Mark III + Purple Stirpe DRG. Pics will be coming after the purple heart head shell is finished.

Still breaking her in. I have been A/B'ing the Mark III black dot and really hearing the nuances between them. They're really not that far apart, but again the 3+ has a more refined tone. I'm more of a metal player and have been primarily on the lead channels.

It's currently loaded with all 6L6 but I intend to get a pair of EL34 to try too very soon

 

[quad48uF]

Been combing through the Mark III+ before and after pics of the board. I attached them for everyone as well.

 

[quad48uF]

Well, here it is. Couldn’t decide to do a wicker or black grill, both looked great. However, when I painted a piece of purple heart black, and re-sanded it so that the black soaked into the grain I knew that my grill was going to be a piece of purple heart. She will be soaking up sunlight for a few more months before going on the shelf. Eventually I’ll do all black hardware.

 

[quad48uF]

Here are some more pics during the build

 

[quad48uF]

Well, here it is. Couldn’t decide to do a wicker or black grill, both looked great. However, when I painted a piece of purple heart black, and re-sanded it so that the black soaked into the grain I knew that my grill was going to be a piece of purple heart. She will be soaking up sunlight for a few more months before going on the shelf. Eventually I’ll do all black hardware.

 

[domct203]

Looks great! Nice job on the dovetails.

Dom

 

[kmanick]

looks killer!!!!! nice work.