guitar amp DIY ?
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I used 6al7s in a 8 watt or so amp kind of based on the deluxe. I used the russian 6sl7s because all the nos and pulls I tried were microphonic.
The 6sl7 might be very good in a champ circuit The one I built from an old PA has to much gain with a 12ay7 and to little with a 12at7. I tried a split plate load resistor on the 2nd stage but it never sounded right with the 12ax7. Funny thing the "best" 12ax7 I tried in it was a japan made one it does not have a brand on it, maybe it is lower gain? Another thing I noted is the amp sounded better with the screen connected direct to the screen supply not using a 470 ohm, I need to rebuild that amp and try a 100 or so ohm screen R and a 6SL7.
A single ef86 to a 6V6 might be very cool. In another thread there are posts about the screen voltages to use in pentodes like the ef86 changing that might get some cool harmonics.
The 6sl7 might be very good in a champ circuit The one I built from an old PA has to much gain with a 12ay7 and to little with a 12at7. I tried a split plate load resistor on the 2nd stage but it never sounded right with the 12ax7. Funny thing the "best" 12ax7 I tried in it was a japan made one it does not have a brand on it, maybe it is lower gain? Another thing I noted is the amp sounded better with the screen connected direct to the screen supply not using a 470 ohm, I need to rebuild that amp and try a 100 or so ohm screen R and a 6SL7.
A single ef86 to a 6V6 might be very cool. In another thread there are posts about the screen voltages to use in pentodes like the ef86 changing that might get some cool harmonics.
ok, after a few weeks of thinking about this, Im gonna try to cram a single ended project in before my next job. Ive been studying this schem for the last two days and am just about ready to pull the trigger on it, working out the layout now. Check it-
http://www.angela.com/catalog/how-to/Super.SE.6V6.html
I have a question- Is there a way that I can put in a switch to put the second 6v6 in and out of the circuit without really complicating things for myself? Im good with pulling one of the rectifiers and leaving the socket open, what happens if I just pull one of the 6v6? I guess the intelligent question is- does the presence of the second tube effect the voltage on the output stage? Doesnt seem like it would but I honestly dont know enough to make an informed guess one way or another.
The audio is coupled to the output stage via the 1.5K resistor to the 6v6, right? I could probably put that resistor on a switch to the lower 6v6 in the diagram. This is assuming I need to leave the second tube in circuit. If not, how could I work a switch to completely kill the second tube all together?
Im at that point with amps where Im starting to come up with ideas but have no idea how to implement them, so frustrating. If anyone can take a quick look, Id really appreciate the help, I suspect what Im trying to do isnt very difficult I hope.
thanks
dave
http://www.angela.com/catalog/how-to/Super.SE.6V6.html
I have a question- Is there a way that I can put in a switch to put the second 6v6 in and out of the circuit without really complicating things for myself? Im good with pulling one of the rectifiers and leaving the socket open, what happens if I just pull one of the 6v6? I guess the intelligent question is- does the presence of the second tube effect the voltage on the output stage? Doesnt seem like it would but I honestly dont know enough to make an informed guess one way or another.
The audio is coupled to the output stage via the 1.5K resistor to the 6v6, right? I could probably put that resistor on a switch to the lower 6v6 in the diagram. This is assuming I need to leave the second tube in circuit. If not, how could I work a switch to completely kill the second tube all together?
Im at that point with amps where Im starting to come up with ideas but have no idea how to implement them, so frustrating. If anyone can take a quick look, Id really appreciate the help, I suspect what Im trying to do isnt very difficult I hope.
thanks
dave
NewYorkDave
Well-known member
I'm afraid it's a little more involved than you think. Pulling one of the 6V6 will not only cause the B+ to rise (because of less current demand on the power supply), it will also cause the voltage drop across the shared cathode resistor to decrease, which means less bias and higher plate current (running hotter). Also, the plate load impedance reflected by the output transformer will need to double. These factors could be mostly overcome by separate cathode resistors and switching arrangements, but you'd be surprised (and probably disappointed) at how little of a volume difference you'd get--only 3dB.
5K:8 output transformers are very common; they're sold in the guitar amp trade as "Champ replacements." I'd build the amp with just 1 6V6 and 1 5Y3. Use an NOS 6V6GT because a Deluxe (or even Champ) power transformer results in pretty punishing B+ by 6V6 standards. "Modern" 6V6s often aren't up to the task. I used to remove a lot of shorted Sovteks from Deluxes, although that was years ago and they may have beefed them up by now.
By the way, the amp will hum like a bitch with the filaments wired as shown (floating). Ground the heater winding centertap, if there is one, or add a 100-ohm, 1-watt resistor from either "leg" of the heater circuit to ground. Look at any old Fender amp schematic for a visual.
5K:8 output transformers are very common; they're sold in the guitar amp trade as "Champ replacements." I'd build the amp with just 1 6V6 and 1 5Y3. Use an NOS 6V6GT because a Deluxe (or even Champ) power transformer results in pretty punishing B+ by 6V6 standards. "Modern" 6V6s often aren't up to the task. I used to remove a lot of shorted Sovteks from Deluxes, although that was years ago and they may have beefed them up by now.
By the way, the amp will hum like a bitch with the filaments wired as shown (floating). Ground the heater winding centertap, if there is one, or add a 100-ohm, 1-watt resistor from either "leg" of the heater circuit to ground. Look at any old Fender amp schematic for a visual.
Jerry
Active member
Dave,
I built that amp - and I'm pretty happy with it. It was my first DIY project - I learned a bunch of good stuff from building it. It really fills the bill for Fender tones. I can't help you with your question about the one vs two tube switch, other than to say that I used the Hammond 125E output transformer which has six different taps that allow for different output impedences. Maybe you could use that TX and an dpdt switch to accomplish what you want to do. Now that I'm thinking about it, I might just try that mod.
When I finished mine, it needed some work. Initially, it didn't work at all, so I took it to a guy who makes a business out of building and repairing amps (Jim at Analog Brothers www.analogbros.com - great guy). He corrected some newbie errors that I had made and gave the amp back to me in a form that made sound for a reasonable fee. To his credit, he didn't correct a really nasty distortion that happened every time I turned it up. It didn't like humbuckers either - more distortion. He did explain where the problem was coming from and let me figure out how to fix it myself. It turned out that the power supply needed toning down. The tubes couldn't dissipate all of the power that they were getting.
I never use two 5y3 rectifiers now. I also put another pi filter (I think that's what its called - two capacitors connected to ground with a resistor in between on the other side) in place of the first capacitor coming out of the power TX (40uf 450V is now 2x 16uf/450V with a 360 ohm 10w resistor between). The combination of these things really tamed the amp and made it useable.
If you like, I can take some voltage measurments - once I got the amp sounding good I never did anything else to it.
I prefer the 6sl7 to the 12ax7 - it sounds rounder. Also, if you have some extra scratch, this amp sounds great through a Celestion Blue Bulldog. Good luck.
I built that amp - and I'm pretty happy with it. It was my first DIY project - I learned a bunch of good stuff from building it. It really fills the bill for Fender tones. I can't help you with your question about the one vs two tube switch, other than to say that I used the Hammond 125E output transformer which has six different taps that allow for different output impedences. Maybe you could use that TX and an dpdt switch to accomplish what you want to do. Now that I'm thinking about it, I might just try that mod.
When I finished mine, it needed some work. Initially, it didn't work at all, so I took it to a guy who makes a business out of building and repairing amps (Jim at Analog Brothers www.analogbros.com - great guy). He corrected some newbie errors that I had made and gave the amp back to me in a form that made sound for a reasonable fee. To his credit, he didn't correct a really nasty distortion that happened every time I turned it up. It didn't like humbuckers either - more distortion. He did explain where the problem was coming from and let me figure out how to fix it myself. It turned out that the power supply needed toning down. The tubes couldn't dissipate all of the power that they were getting.
I never use two 5y3 rectifiers now. I also put another pi filter (I think that's what its called - two capacitors connected to ground with a resistor in between on the other side) in place of the first capacitor coming out of the power TX (40uf 450V is now 2x 16uf/450V with a 360 ohm 10w resistor between). The combination of these things really tamed the amp and made it useable.
If you like, I can take some voltage measurments - once I got the amp sounding good I never did anything else to it.
I prefer the 6sl7 to the 12ax7 - it sounds rounder. Also, if you have some extra scratch, this amp sounds great through a Celestion Blue Bulldog. Good luck.
NewYorkDave
Well-known member
Well, if you insist, give this simple mod a try first. It may be enough to satisfy, and it's continuously variable to boot:
EDIT Whoops! Brain fart! I drew it as a push-pull output out of force of habit. I'll fix the sketch and re-post.
(A few minutes go by...) OK, it's fixed now.
By the way, even though I didn't draw them in, I would add some screen-grid current limiting resistors if I were building this amp.
EDIT Whoops! Brain fart! I drew it as a push-pull output out of force of habit. I'll fix the sketch and re-post.
(A few minutes go by...) OK, it's fixed now.
By the way, even though I didn't draw them in, I would add some screen-grid current limiting resistors if I were building this amp.
AnalogPackrat
Well-known member
[quote author="NewYorkDave"]
5K:8 output transformers are very common; they're sold in the guitar amp trade as "Champ replacements." I'd build the amp with just 1 6V6 and 1 5Y3. Use an NOS 6V6GT because a Deluxe (or even Champ) power transformer results in pretty punishing B+ by 6V6 standards. "Modern" 6V6s often aren't up to the task. I used to remove a lot of shorted Sovteks from Deluxes, although that was years ago and they may have beefed them up by now.
[/quote]
Try the JJ's 6V6 and 6L6 tubes. They seem to take a beating like the old American tubes did. Not too pricey either. I am not affiliated, just have bought a few from EuroTubes:
http://www.eurotubes.com/index.htm
5K:8 output transformers are very common; they're sold in the guitar amp trade as "Champ replacements." I'd build the amp with just 1 6V6 and 1 5Y3. Use an NOS 6V6GT because a Deluxe (or even Champ) power transformer results in pretty punishing B+ by 6V6 standards. "Modern" 6V6s often aren't up to the task. I used to remove a lot of shorted Sovteks from Deluxes, although that was years ago and they may have beefed them up by now.
[/quote]
Try the JJ's 6V6 and 6L6 tubes. They seem to take a beating like the old American tubes did. Not too pricey either. I am not affiliated, just have bought a few from EuroTubes:
http://www.eurotubes.com/index.htm
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