6V6's/class A in a Mark IV?
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musicbox
Well-known member
sounds like a pretty deffinitive answer to me. 
anyone know why not?
anyone know why not?
brett336
Member
It has to do with the plate voltages that the 6v6 tube sees. The way that Mesa designed the amp, the plate voltages fall just within spec for most 6V6 tubes only when the amp is in Simul-class and tweed. I think you are also supposed to run the 8 ohm speaker/cab into the 4 ohm output jack to take some of the load off of the tubes.
In that past, I have inadvertantly run 6v6 tubes in Class-A with out any issues. Although, I was not playing for more that 30min before I noticed my error. Never-the-less, I think that all you would get is MUCH shorter tube life; but I don't know how much shorter.
Any good amp tech that knows Boogie will correct me if I am wrong...
I'm sure of that!
In that past, I have inadvertantly run 6v6 tubes in Class-A with out any issues. Although, I was not playing for more that 30min before I noticed my error. Never-the-less, I think that all you would get is MUCH shorter tube life; but I don't know how much shorter.
Any good amp tech that knows Boogie will correct me if I am wrong...
I'm sure of that!
I did the same thing. Class A in the 8 ohm Output Jack. Wow, what a tone.
I am experimenting with lowering the Voltages in my Mark IV. I will post the results in a few weeks. Most of the mods might include drilling a new hole in the chassis though. My amp is new, and will never be a "Collector's Item" so I really don't care. If you have an older one though, you would probably not want to do this.
I will be lowering the B+ Voltage, as well as providing Adjustable Bias for each Power Tube, or possibly just for the "Simul-Class" tubes. This will allow me to run any combination of tube that I want.
brett336
Member
I would really be interested to know how you mod turns out. Maybe you could post a "How-To" or some pic's on this thread when you get done.
I may want to do it to my MkIV also.
Please let us know!
I may want to do it to my MkIV also.
Please let us know!
It might be a couple of weeks before I can get to it. I have a bunch of amps to repair and a couple to build.
I will definitely post the results and exactly what I did once I get it done.
I will definitely post the results and exactly what I did once I get it done.
I'll be trying the mods out after New Year's.
As for the Impedance questions:
I found this same information in several books and on the Fender Forum, www.fdp.com.
"Boy, we've been dragging this one out a lot, as of late: JJ 6V6's will handle that plate voltage quite
easily. This is one tough, modern 6V6.
The impedance figure will double, i.e.: an 8 ohm amp will be 16 ohms, a 4 ohm amp will be 8 ohms. And
of course check the bias.
I use JJ 6V6s in a 6L6 amp with plate voltages of 420 and 1K screen resistors. I have had no problems
and its been gigged many times.
FWIW, my 1967 tube caddy shows the 6V6 as a replacement for the 6L6.
One concern is the mismatched load (6V6s want to see 2X the output load for 6L6s) but they'll probably
still last 1/2 as long (or longer) than usual."
I never received a reply for my email to Mesa concerning this. I'm currently running my Mark IV with the 6V6's and using the 8 ohm speaker jack. The tone is awesome and the output is much lower than in the 4 ohm setting.
All of the research that I have gone through suggests that the Mesa manual is wrong and the amp needs to be run on the 16 ohm setting instead of the 4 ohm setting.
Maybe Mesa has us use the 4 ohm settings so that the Volume won't be affected much.
THD's Andy Marshall, and Kevin O'Connor from London Power (author of The Ultimate Tone series of books) both told me that the Impedance setting of a transformer is merely a convenience, not a necessity. The amps are designed around a certain, "Optimal" impedance setting of the transformers, based on the desired tones the designers are looking for. This setting can be altered to acheive other sounds.
I will keep you guys posted.
I had a THD Plexi combo for a while that had a switch on the back to adjust the output and response of the amp. The switch actually switched between the 4 & 8 ohm settings on the output transformer. The difference was incredible. With the 4 ohm setting, the amp was bold, in your face, great clean headroom. On the 8 ohm setting, the amp was sweet, mellow, and creamy, with plenty of distortion at lower volumes.
I think it is safe to experiment, but I don't want anybody to go out and blow up their amps.
I'll post back in a couple of weeks and let you guys know how my amp is holding up.
I just got hired by a local band, so I'll finally be using my gear again. It's been 3 1/2 years, since our oldest son was born. I took some time off to be with my family, but now I've got the serious itch to play.
As for the Impedance questions:
I found this same information in several books and on the Fender Forum, www.fdp.com.
"Boy, we've been dragging this one out a lot, as of late: JJ 6V6's will handle that plate voltage quite
easily. This is one tough, modern 6V6.
The impedance figure will double, i.e.: an 8 ohm amp will be 16 ohms, a 4 ohm amp will be 8 ohms. And
of course check the bias.
I use JJ 6V6s in a 6L6 amp with plate voltages of 420 and 1K screen resistors. I have had no problems
and its been gigged many times.
FWIW, my 1967 tube caddy shows the 6V6 as a replacement for the 6L6.
One concern is the mismatched load (6V6s want to see 2X the output load for 6L6s) but they'll probably
still last 1/2 as long (or longer) than usual."
I never received a reply for my email to Mesa concerning this. I'm currently running my Mark IV with the 6V6's and using the 8 ohm speaker jack. The tone is awesome and the output is much lower than in the 4 ohm setting.
All of the research that I have gone through suggests that the Mesa manual is wrong and the amp needs to be run on the 16 ohm setting instead of the 4 ohm setting.
Maybe Mesa has us use the 4 ohm settings so that the Volume won't be affected much.
THD's Andy Marshall, and Kevin O'Connor from London Power (author of The Ultimate Tone series of books) both told me that the Impedance setting of a transformer is merely a convenience, not a necessity. The amps are designed around a certain, "Optimal" impedance setting of the transformers, based on the desired tones the designers are looking for. This setting can be altered to acheive other sounds.
I will keep you guys posted.
I had a THD Plexi combo for a while that had a switch on the back to adjust the output and response of the amp. The switch actually switched between the 4 & 8 ohm settings on the output transformer. The difference was incredible. With the 4 ohm setting, the amp was bold, in your face, great clean headroom. On the 8 ohm setting, the amp was sweet, mellow, and creamy, with plenty of distortion at lower volumes.
I think it is safe to experiment, but I don't want anybody to go out and blow up their amps.
I'll post back in a couple of weeks and let you guys know how my amp is holding up.
I just got hired by a local band, so I'll finally be using my gear again. It's been 3 1/2 years, since our oldest son was born. I took some time off to be with my family, but now I've got the serious itch to play.
