I did the same thing, the Mark V was the next best thing and found it was not. Should have held onto my Mark III comb. That amp was always a pleasure to play though.
What power tubes have you used in the Mark V90 in terms of 6L6GC?
Wow Bandit, you have a great amp collection.
It makes me a lot happier to understand that you and others have gone through something similar to me.
My only other tube amp before the Mark V was a 100W Yamaha designed by Soldano that I sold, and kind of wish I’d hung onto it and modded it to perfection. It was a cool amp with great transformers I think and some flaws, and I had 6L6s in it and we didn’t get along. Then I had the Mark V with the 6L6GC set it came with and I was so convinced it was going to be the perfect thing. And as I found I couldn’t play for a long time without hurting my hearing I ended up having this bad association with the 6L6 tubes. I’ve found now that my high frequency hearing is impaired on the side the amp was on during those years. And I wasn’t playing super loud or for very long. In a very simpleminded way I ended up deciding incorrectly that the tube type itself was the cause of my ears ringing after playing. I tried the EL84 adapters early on but they don’t make everything better, nor do to JJ EL34s, even though I like the sound a little better that way. I mean I think the different tubes cause the amp to have a different frequency response in broad terms, but the real issue has got to be more than that.
I’ve briefly put those sweet Tung Sol 5881 tubes in the amp and they sound good but the mystery problem is still a mystery. I have some chores to do and when I finish, as a reward, I’m going to record the Boogie and search for the problem with the spectrum analyzer. I also have a kind of crude USB oscilloscope and I’ll try to record with that in case the problem frquency is too high for the audio interface. I have a function generator too, and the amp’s square wave response might be revealing.
I am going to make the preamp changes for sure, and find the best power tubes. Because to my ears the preamp could sound better. But the priority has to be the mystery problem. I hope to make some change to the power amp circuit to fix this. Then maybe I really should add bias test points and bias adjustment pots, and voice the amp just the way I like it best. It is never going to sound like a Marshall anyway so maybe I will like the 5881 tubes or a great 6L6 or even a quad of 6V6 tubes, or some simul-mixture of those. It could still become an amazing amp.
What I have used that sounded epic: SED =C= 6L6GC, they are a bit bright but really help with the sterile effect. It is too bad they are out of production and very difficult to find. The Mesa STR441 were also a huge improvement over the STR440 tubes. I have tried many other power tubes to no avail of any satisfaction. STR448 did not work out. I know for a fact my Mark V90 is not on par with the other amps out there. It started out as a head but got replaced by a Roadster, so I converted it to a combo with the intent of using an EVM12L speaker with it. This also helped with the chassis overheating issue which was related to the bias being way off. I could not run any of the STR440 tubes in the amp as it would result in red plating the center pair. Sometimes it would take 20 minutes or longer and sometimes it was an instant kill of the tubes. SED=C= 6L6GC would survive and never failed, I still have those tubes and they work fine and test like new. I did change the one bias resistor 82.5k to a 91k (measured at 86k ohms). It was not until I saw how the power meter on the rock crusher was pegged at 150Wrms peak constantly when I was running with that. No wonder why I kept blowing out speakers in the combo or red plating most tubes I tried with it. I do not have much faith in the amp as it is, so many issues to mention, blown screen resistors, a few JFETS died, lost the reverb and now I cannot use the amp without the footswitch connected, before it was the other way, if I used the footswitch it did weird stuff. Ground issue in the cable and other problems. Variac power mode usually resulted in tube death so had to run at full power. Just do a search on my username in the Mark V forums, I still wonder why I have it to this day. I should have sold it and got another if that was what I was after.
That is all fascinating. I’ve read some of your accounts of your initial excitement for the amp and your gradual disillusionment and eventual disgust, and it seems very reasonable given the series of things that happened. You had that red plate problem that I never have, and other problems too.
Because I decided not to put Mesa tubes in my amp again I just run variac mode and EL34s and have the bias meter to double check. In variac mode the EL34s are looking about right. Maybe 35mA for the hot pair? I don’t remember exactly now, but it seemed ok in Variac mode and too hot in Normal mode, and I think variac mode was what the manual said to do for EL34s anyway.
So far I’ve just played around with the Bogner Ecstasy mini as a substitute power amp. But I‘m going to try also with my Shiva 80W 2xEL34 amp. It has direct power amp input separate from the effects loop, and it’s a beautiful, dark-voiced thing. It should give some confirmation of previous observations. If it makes everything good then I know all I need to do is rework the part of the Mark V circuit after the effect out or line out, etc.
One thing I know about analog circuit design is that the stack up of component tolerance differences is one of the biggest obstacles. Because even when purchased components meet all their specs the tolerance variations are often not random but systematically skewed in some way. For example sometimes 5% resistors and 1% resistors come from the same manufacturing runs, so in that case no 5% resistor is within +/- 1% of the stated value. Or maybe a whole run of parts will be skewed the same direction. This ends up meaning that unless the designer is very careful the finished products will not always work correctly without testing and rework.
Old tube amps don’t have to worry so much. They have few parts and the stack up of errors is not too bad. Also the compensation schemes were established long ago and everyone knows about them. Things like bias pots and matched tubes will make everything good. The Mark V really pushes into a place of normal/modern amounts of complexity and the designers just might not be up to the task or might have to learn new tricks before they can ship a reliable product. JFETs in particular just have a huge spread over some of their parameters. And they notoriously do assign part numbers after testing those.
And there are decisions in the Mark V that I think are just design errors. Like using a 1000V 1N4007 diode with a very low current rating in the 12V supply. I didn’t try to work out the 12V power budget, but looking at what happens there I thought it might be good to have something with a better current rating. Mesa says the problem was a bad batch of parts, but I replaced those with 1N4003 diodes in my amp. I didn’t necessarily analyze everything correctly to make that decision, and there would have been better diodes that I didn’t happen to have on hand, but I no longer have confidence that Mesa analyzed the component selection either.
That is why I am willing to bet that so many Mark V amps sound great and others have problems, and a few just try to cook their tubes. It is no secret that some of these amps are lemons, and the resale values reflect that. If Mesa would have documented what they learned after shipping then we would have fixed our amps already and the value-sucking cloud of uncertainty around them would dissipate. It is a bit of a challenge for us as customers to diagnose and fix these complex problems. This is as much of a support issue as a collection of design mistakes. To me the question about a company like this is whether they are a trustworthy partner for their customers. And I feel like my amp can potentially be saved, but if I gave Mesa any more money in the future I’d feel like a real sucker.
Good old sounds of a cranked Marshall, yep. Me too. That is why I have the Badlander, RA100, Marshall Silver Jubilee 2555x. The EVH 5150 IIIs EL34, a bit noisy but had it out not too long ago and though it sounded good. I did not like it much when I first got it.
Those are so great. That RA-100 in particular just sounds like a kingly amp. Yet another Marshall that is better than the real Marshall it most resembles.
If you could only have either the Silver Jubilee 2555X head or the RA-100 head, or one Badlander, which would you keep?
Every one of those amps you have seems wonderful to me. I feel right now like I can meet all my needs with the Shiva alone, but every one is special.
Something you are doing that I’d also like to try are stereo side or rear channels. Did you see the Bogner Duende Seco Mojado in earlier times? Super wonderful living room amp with tube tremelo on two 6x9 square speakers for side channels (maybe 5W each?) and an improved 2x 6V6 Fender Delux in the center. It looked like a labor of love. I’ve sometimes set up a second amp behind me with delay-only for an echo but that is all I’ve tried. The hot way to do that would be with stereo mic pair, preamps and a stereo delay, to enhance the actual room echo. And it would take compression or some other active dynamics to keep the echos under control. Maybe the mics are carotids that face the center cab. The idea would be to get the particular room sound, which is so recognizable to our ears, but expanded.
. I do tend to be pessimistic on the MKV90. Even with preamp changes and such, I barely ever use the amp as that in the room sound is not much to my liking. Sure, it records well as the mics will not capture the overtones and such. Since I got the JP2C and more recently the Mark VII, I see no purpose on torturing myself with the MKV90 any longer. May as well be water-boarding.
