In general the 6v6's supply a punchy rythmic drive to music while el84's are have a chimey, bell like quality. Together they work well together with the 6v6's supplieing most of the bass and the el84s providing the upper end. They also work well together because with the 6v6 sound becomes bloated if over driven. Conveniently the 6v6 normal bias point is several volts more negative than the el84 so that when you are starting to overdrive the el84's, which don't sound too bad even then, the 6v6s are still well within class A and supply a tight bass structure to the music. Thats assuming the same signal voltage input to both tubes anddifferent bias voltages (cathode or otherwise)for the el84 and 6v6.
I have an old Guild Ultraflex that has two complete power amp sections. Each has slightly different voicing even they both use 7591's.There is a balance control (the Ultraflex knob) to control the amount of signal to each amp. One amp plays through an 8 inch speaker and the other through a 12 inch speaker. This amp can provide the widest array of tonal character of any guitar amp that I have heard. That is where I got the idea.
There are several ways to do this. The simplest is to use a dual ganged linear taper pot with each section wired like a master gain pot, but the ends swapped on one section, so that one is all the way up when the other is all the way down. Then as with a master gain the center pins go to each output tube.
There is another way. Your original schematic shows the grids of each output tube wired together. There should be a resistor from the grids to ground. Seperate the two grids and use two coupling caps. Use a seperate resistor for each output tube but instead of tying them both to ground, wire them to each end of a pot and ground the center pin. Some experimentation will be needed to come up with resistor values to get the sound you want and you could even use different coupling cap values for each tube.
I used to play guitar. Now I just punish my neighbors! Seriously my guitar playing skills peaked when I was about 15 or 16 years old. Then I went to a Jimi Hendrix concert and decided that I would never be a real guitar player!
No need to, it can be used as an audiophile amp. Come on, you can be the first DIYer to make an amp sporting four EL84s and two 6V6s per channel.
Stereophile: Mesa Tigris integrated amplifier
I think I may have read that review before. It probably helped in getting me to purchase the Tigris in the first place. There is a notable problem in the review though when it references the tigris as being class A. Only the 6v6 is running "approximately" class A. The el84 is definitely not. The reviewer actually states that and then seems to get confused later by Mesa's own promotional material.
I should add one more thing that is very important and goes to the reliability of this product: average current draw of a tube when switching from simulated triode to pentode mode. Idling current normally changes somewhat when the screen voltage is moved from the plate connection to the (almost)B+ connection. This is where you run into problems even (with) cathode bias. My amp would simply draw too much current with many off the shelf 6v6 and el84 tubes because there was no modification for bias adjustment when that screen voltage input was changed. To do this kind of amp right really REQUIRES availability of bias adjustment that coincides with switching between simulated triode mode and pentode mode.
But its still a great idea and worth building ones own. I have my own ears to prove it.
Eric
I should add one more thing that is very important and goes to the reliability of this product: average current draw of a tube when switching from simulated triode to pentode mode. Idling current normally changes somewhat when the screen voltage is moved from the plate connection to the (almost)B+ connection. This is where you run into problems even (with) cathode bias. My amp would simply draw too much current with many off the shelf 6v6 and el84 tubes because there was no modification for bias adjustment when that screen voltage input was changed. To do this kind of amp right really REQUIRES availability of bias adjustment that coincides with switching between simulated triode mode and pentode mode.
But its still a great idea and worth building ones own. I have my own ears to prove it.
Eric
Well, I have downloaded the Tigris manual, no schematic on it but now I have a pretty good idea how it works. Two rows of 2 el84s and one 6v6 per channel.
I'm finishing the guitar amp and my dilemma now is if I complicate the design a little more installing a switch to mix pentode and triode output.
I think I will first tweak it to work only in pentode mode; later on I'll experiment with the 50% triode 50% pentode madness.
I will post the results.
I'm finishing the guitar amp and my dilemma now is if I complicate the design a little more installing a switch to mix pentode and triode output.
I think I will first tweak it to work only in pentode mode; later on I'll experiment with the 50% triode 50% pentode madness.
I will post the results.
Sorry I've been dormant for so long - I'm in the process of studying for my Fundamentals of Engineering licensing exam = absolutely no free time!
Tubelab- thanks for the detailed response- once i get to testing ill be sure to try both and see which sounds best.
Although it looks like stalker is going to beat me to the punch with a working prototype first! I'm a little jealous, but anxious to see how it turns out... Stalker-once you get it working would you mind posting a schematic that shows some of the component values you chose? Once I start building mine I will no doubt experiment to my tastes but having a good starting point would be greatly appreciated!!
Tubelab- thanks for the detailed response- once i get to testing ill be sure to try both and see which sounds best.
Although it looks like stalker is going to beat me to the punch with a working prototype first! I'm a little jealous, but anxious to see how it turns out... Stalker-once you get it working would you mind posting a schematic that shows some of the component values you chose? Once I start building mine I will no doubt experiment to my tastes but having a good starting point would be greatly appreciated!!
. Stalker-once you get it working would you mind posting a schematic that shows some of the component values you chose? Once I start building mine I will no doubt experiment to my tastes but having a good starting point would be greatly appreciated!!
I will, you gave me the idea so I owe you something.
I so resemble that. I tried to play a guitar once but could never manage to stop just one string with my short, stubby, and chubby fingers (just like the rest of me). I figure that when it comes to strings I will have to try bass guitar or cello.
mike
Legal disclosure
I figure I better mention this now before anyone takes it on the chin financially. Most of us here, including me, are doing tube audio strictly for ourselves and not for profit. However there is a patent regarding certain technologies involved in using two different types of tubes. Here's a description of the one relating to the Mesa Boogie tigris I own:
United States Patent: 5559469
It doesn't strictly apply to the amp but rather to using a switch to switch in different tube pairs and combinations to power it. It is a current patent from what I can see - i.e. it was filed in 1994. So though I don't know the exact term that patents are granted I figure it still has a year or two to go. And though it doesn't strictly apply to the Tigris in all aspects (switching whole tubes in and out of circuit), you only have to read it to see that the tigris originated from this patent. And Mesa DOES go after small producers using their intellectual property. They have a rep. So using general common sense I would figure one would probably be safe from liability as long as money does not change hands on an amp you build that uses that idea.
As far as the idea of building amps that operate in simultaneous switchable classes of operation, i.e. pentode and triode, of the same tube type: That patent is expired. Here it is:
United States Patent: 4713624
This may seem like hogwash to many of you. I know a lot of people who resent the company for locking up good ideas. Many people even think they didn't originate some of these ideas. I have no affiliation with them but I think its better to be prepared just in case. caveat emptor.
Eric
I figure I better mention this now before anyone takes it on the chin financially. Most of us here, including me, are doing tube audio strictly for ourselves and not for profit. However there is a patent regarding certain technologies involved in using two different types of tubes. Here's a description of the one relating to the Mesa Boogie tigris I own:
United States Patent: 5559469
It doesn't strictly apply to the amp but rather to using a switch to switch in different tube pairs and combinations to power it. It is a current patent from what I can see - i.e. it was filed in 1994. So though I don't know the exact term that patents are granted I figure it still has a year or two to go. And though it doesn't strictly apply to the Tigris in all aspects (switching whole tubes in and out of circuit), you only have to read it to see that the tigris originated from this patent. And Mesa DOES go after small producers using their intellectual property. They have a rep. So using general common sense I would figure one would probably be safe from liability as long as money does not change hands on an amp you build that uses that idea.
As far as the idea of building amps that operate in simultaneous switchable classes of operation, i.e. pentode and triode, of the same tube type: That patent is expired. Here it is:
United States Patent: 4713624
This may seem like hogwash to many of you. I know a lot of people who resent the company for locking up good ideas. Many people even think they didn't originate some of these ideas. I have no affiliation with them but I think its better to be prepared just in case. caveat emptor.
Eric
Last edited:
exeric- that issue did occur to me, and as I recall, Egnater amplification ran into issues with Mesa regarding this very same issue for their Rebel line of guitar amps (of which I'm a happy owner of and where I got this idea in the first place )- to get around it they made the tubes blendable instead of footswitchable, thus avoiding any legal issues. Although I have yet to prototype my design, the thought of making these amps for profit if they are successful has crossed my mind and I am still entertaining it. Occurring to forums I've read on the net and the linked patent, If I do sell these for profit, then hopefully I should be fine as long as I don't incorporate any form of selection-bypass switching with the output valves, I haven't checked into any patents regarding blending though...
It is unfortunate that such simple ideas that have the potential for such fun tonal pallets are on lock down! Thank you for the research and and good, valid points, I, and I'm sure many others, appreciate it! Hopefully others will see this page and avoid any issues as well.
)- to get around it they made the tubes blendable instead of footswitchable, thus avoiding any legal issues. Although I have yet to prototype my design, the thought of making these amps for profit if they are successful has crossed my mind and I am still entertaining it. Occurring to forums I've read on the net and the linked patent, If I do sell these for profit, then hopefully I should be fine as long as I don't incorporate any form of selection-bypass switching with the output valves, I haven't checked into any patents regarding blending though... It is unfortunate that such simple ideas that have the potential for such fun tonal pallets are on lock down! Thank you for the research and and good, valid points, I, and I'm sure many others, appreciate it! Hopefully others will see this page and avoid any issues as well.
I'm sure that if push comes to shove, prior art could be found for many of those patents and thus invalidated. Most are also easy circumvented, such as using a midi controller input instead of a footswitch. Then the customer just buys a separate midi footswitch.
If you're a DIY builder occasionally selling an amp to a befriended musician, or even on an online auction site marking it clearly as a DIY amp, there's no way they can come after you and make a valid case in court.
Kenneth
If you're a DIY builder occasionally selling an amp to a befriended musician, or even on an online auction site marking it clearly as a DIY amp, there's no way they can come after you and make a valid case in court.
Kenneth
I'll be honored if Mesa got interested in my DIY hobby.
Youngb4 I'm installing right now the triode/pentode switch.
Still, I won't have time to jam with a friend until this weekend. My guitar playing is just OK, rhythm player only (crap with solos) so I need him (he's a professional) to fully test the amp.
Schematic will be ready in a couple of days.
Youngb4 I'm installing right now the triode/pentode switch.
Still, I won't have time to jam with a friend until this weekend. My guitar playing is just OK, rhythm player only (crap with solos) so I need him (he's a professional) to fully test the amp.
Schematic will be ready in a couple of days.
My bad. The patents for Mesa's "simulclass" pentode/triode switching, which are expired, is this:
United States Patent: 4593251
and this
United States Patent: 4532476
By the way the patent I accidentally referenced is a very interesting one. It supposedly allows one to get more dynamic touch when playing guitar. I might even experiment with putting it in an amp I eventually build just in case I ever want to (try) to learn guitar. It would also be interesting to see what it does to recorded music. That patent is also expired.
Eric
Exeric, thanks for those interesting links.
I was but at the last minute I changed my mind. Pentode preamp this time, bored of doing the Fender Champ preamp over and over. A great sounding one btw.
This is the preamp I'm using, it was good for my VOX inspired 15W guitar amp but if I don't like it in an SE output stage I'll go back to Fender.
I was but at the last minute I changed my mind. Pentode preamp this time, bored of doing the Fender Champ preamp over and over. A great sounding one btw.
This is the preamp I'm using, it was good for my VOX inspired 15W guitar amp but if I don't like it in an SE output stage I'll go back to Fender.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.