One of my questions lately too, besides others, does anyone have a great link to a DIY project or schematic or brand/name/model of any great amp using 2 6V6's in push-pull, with some audio control pots, etc for a decent guitar amp?
I'm seeing at lot of circuits on places like Duncan's & MachMat, etc, but what's someone's real fave for sound simplicity, etc. ?
Don't need quite the power of 6L6's, and would like to keep the project more retro, and use a single Jensen P12R speaker as well.
From all my schematic-searching travels, this one seems easy, diodes for the power supply, a single 12AX7 and two 6V6GT's, and it's an original Fender schematic, a Musicmaster Bass produced from 1970-1982.
The only new thing to me is the 026847 interstage audio transformer, is this unique, or are there other items that will do for this?
Also, any critiques on the design would be appreciated, I'm hoping to use it for audio / treble guitar as well, just mostly as a fun project.
Do you think this is a good one to try?
Also if this seems good to go, can you suggest any simple easy mods for more audio control, like "bright", etc....
Thanks
I'm seeing at lot of circuits on places like Duncan's & MachMat, etc, but what's someone's real fave for sound simplicity, etc. ?
Don't need quite the power of 6L6's, and would like to keep the project more retro, and use a single Jensen P12R speaker as well.
From all my schematic-searching travels, this one seems easy, diodes for the power supply, a single 12AX7 and two 6V6GT's, and it's an original Fender schematic, a Musicmaster Bass produced from 1970-1982.
The only new thing to me is the 026847 interstage audio transformer, is this unique, or are there other items that will do for this?
Also, any critiques on the design would be appreciated, I'm hoping to use it for audio / treble guitar as well, just mostly as a fun project.
Do you think this is a good one to try?
An externally hosted image should be here but it was not working when we last tested it.
Also if this seems good to go, can you suggest any simple easy mods for more audio control, like "bright", etc....
Thanks
Hi FRANK 754 ,
I don’t have any site or link to suggest , BUT I strongly
recommend that you go fast to buy the book :
“The Tube Amp Book “ , written by Aspen Pittman , a
very nice guy , from California , that knows almost
everything about tube amps for guitars .
He is the owner of ” Groove Tubes” , too .
The book has two parts : 1st A comprehensive history
of tube guitars amps and 2nd A complete schematic
archive with A LOT of schematics from many manu-
facturers and a CD with 800 schematics in pdf files .
Most of them , using 6V6 GT tubes .
My post , is not an advertising BUT only a “tip” to
suggest an excellent bibliography .
Certainly you will find there a good design .
Regards ,
Carlos
I don’t have any site or link to suggest , BUT I strongly
recommend that you go fast to buy the book :
“The Tube Amp Book “ , written by Aspen Pittman , a
very nice guy , from California , that knows almost
everything about tube amps for guitars .
He is the owner of ” Groove Tubes” , too .
The book has two parts : 1st A comprehensive history
of tube guitars amps and 2nd A complete schematic
archive with A LOT of schematics from many manu-
facturers and a CD with 800 schematics in pdf files .
Most of them , using 6V6 GT tubes .
My post , is not an advertising BUT only a “tip” to
suggest an excellent bibliography .
Certainly you will find there a good design .
Regards ,
Carlos
Frank,
It's a fact of life that the transformers ("iron") are a major part of the cost of any tube power amp project. Even IF it's available, that phase splitter trafo is going to put some sort of dent in your bank balance.
Those of us involved in the "El Cheapo" project went to GREAT lengths to control "iron" costs. Advantage was taken of an inexpensive replacement O/P trafo for Fender Deluxe guitar amps in the HIFI amp. "What goes around, comes around." You use can most of the "El Cheapo" circuitry to advantage in your MI project. Not having to worry about deep bass, allows the use of the available ultralinear taps. The 'AQ5 "El Cheapo" uses is electrically "equivalent" to the 6V6. So, component value changes are not necessary. Whether or not you retain the loop NFB is up to you.
Since a MI amp has only 1 channel, you could use a Triad N-68X in the voltage doubler. Other savings are possible too. 470 muF. 'lytics in the doubler stack are but 1 example.
edit: fixed typo
It's a fact of life that the transformers ("iron") are a major part of the cost of any tube power amp project. Even IF it's available, that phase splitter trafo is going to put some sort of dent in your bank balance.
Those of us involved in the "El Cheapo" project went to GREAT lengths to control "iron" costs. Advantage was taken of an inexpensive replacement O/P trafo for Fender Deluxe guitar amps in the HIFI amp. "What goes around, comes around." You use can most of the "El Cheapo" circuitry to advantage in your MI project. Not having to worry about deep bass, allows the use of the available ultralinear taps. The 'AQ5 "El Cheapo" uses is electrically "equivalent" to the 6V6. So, component value changes are not necessary. Whether or not you retain the loop NFB is up to you.
Since a MI amp has only 1 channel, you could use a Triad N-68X in the voltage doubler. Other savings are possible too. 470 muF. 'lytics in the doubler stack are but 1 example.
edit: fixed typo
Thanks, that's some great info, and I do like el cheapo info as well,
seems like a great circuit.
I did a bit of research on the original xfmr on that schematic I posted above
and it is obsolete and unavailable. One one usenet board someone had
exactly the same question, and it was suggested to check the antique
electronics site for similar items, I found these that might work, only
thing is that I can't really guess at the turns ratio, but these are interstage
xfmrs for phase splitter circuits with a secondary center tap:
Hammond P-T124B 10K PRI 90K SEC CT $24.95
http://www.tubesandmore.com/scripts...levclients/cemirror/ELEVATOR.FXP?item=P-T124B
Hammond P-T124D 7K PRI, 15.8K SEC $18.95
http://www.tubesandmore.com/scripts...levclients/cemirror/ELEVATOR.FXP?item=P-T124D
Hammond P-T124E 15K PRI, 33.8/135K S $23.95
http://www.tubesandmore.com/scripts...levclients/cemirror/ELEVATOR.FXP?item=P-T124E
Hammond P-T156 $15.70
Equivalent to Stancor A53-C. 1:3 ratio overall. Center tapped secondary may be used for push-pull grids. Max. Primary Current: 10 mA Impedance Primary to Secondary (Ohms): 10,000 to 90,000
http://www.tubesandmore.com/scripts...elevclients/cemirror/ELEVATOR.FXP?item=P-T156
Is this question related to the characteristics of the output of the 12AX7 or is it
anyone's choice based on the factor you want. In this case what would be anyone's
guess as to the original xfmr? Would the 10K to 90K be a good bet?
seems like a great circuit.
I did a bit of research on the original xfmr on that schematic I posted above
and it is obsolete and unavailable. One one usenet board someone had
exactly the same question, and it was suggested to check the antique
electronics site for similar items, I found these that might work, only
thing is that I can't really guess at the turns ratio, but these are interstage
xfmrs for phase splitter circuits with a secondary center tap:
Hammond P-T124B 10K PRI 90K SEC CT $24.95
http://www.tubesandmore.com/scripts...levclients/cemirror/ELEVATOR.FXP?item=P-T124B
Hammond P-T124D 7K PRI, 15.8K SEC $18.95
http://www.tubesandmore.com/scripts...levclients/cemirror/ELEVATOR.FXP?item=P-T124D
Hammond P-T124E 15K PRI, 33.8/135K S $23.95
http://www.tubesandmore.com/scripts...levclients/cemirror/ELEVATOR.FXP?item=P-T124E
Hammond P-T156 $15.70
Equivalent to Stancor A53-C. 1:3 ratio overall. Center tapped secondary may be used for push-pull grids. Max. Primary Current: 10 mA Impedance Primary to Secondary (Ohms): 10,000 to 90,000
http://www.tubesandmore.com/scripts...elevclients/cemirror/ELEVATOR.FXP?item=P-T156
Is this question related to the characteristics of the output of the 12AX7 or is it
anyone's choice based on the factor you want. In this case what would be anyone's
guess as to the original xfmr? Would the 10K to 90K be a good bet?
OK, am researching, will look for something similar with perhaps one more tube,
this one seemed real "smooth" in design because of the transformer as a feature,
as I hadn't seen that design too often.
On overtaxing the second triode, are you saying this because the voltage is high,
and perhaps the 15k resistor across the interstage primary could stand to be
boosted up a bit to lower the plate voltage?
Also, though, on the plates of the 6V6's, isn't the 290v a bit conservative and
could stand a bit more to boost final stage power, perhaps a bigger power transformer
with more going to the last stage, but a bit less to the second triode?
this one seemed real "smooth" in design because of the transformer as a feature,
as I hadn't seen that design too often.
On overtaxing the second triode, are you saying this because the voltage is high,
and perhaps the 15k resistor across the interstage primary could stand to be
boosted up a bit to lower the plate voltage?
Also, though, on the plates of the 6V6's, isn't the 290v a bit conservative and
could stand a bit more to boost final stage power, perhaps a bigger power transformer
with more going to the last stage, but a bit less to the second triode?
Sticking with the authentic Fender designs, for example, there's this one
(the Harvard 5F10) at 10 watts which seems very do-able and simple with a straight
3 element all-tube preamp section. This seems the most straightforward:
The only other in this simplicity range is the vibrolux 5F11 which seems
to have some nice tweaks, but not a huge project, maybe this is the better bet:
(the Harvard 5F10) at 10 watts which seems very do-able and simple with a straight
3 element all-tube preamp section. This seems the most straightforward:
An externally hosted image should be here but it was not working when we last tested it.
The only other in this simplicity range is the vibrolux 5F11 which seems
to have some nice tweaks, but not a huge project, maybe this is the better bet:
An externally hosted image should be here but it was not working when we last tested it.
It is a simpel design yes. Build it if you like! don't let me stop you. I was just offering an alternative to expensive transformers.frank754 said:
Not the voltage: the current. That 15k resistor is letting way too much current through. I'd make it more than 47k, or maybe leave it out altogether.
Not really, I guess it depends how much power you want out, but there's not a lot in it. A lower anode voltage allows you to run more in CLass A, which is reputed to have the sweetest distortion.
There seems to be a bit of a vogue for very high anode voltages at the moment, there's no real need for it. If I want more power I don't thrash my wee little valves, I just move up to bigger ones. Use whatever voltage you can buy (What I mean is; build the amp to suit the transformers available, not the other way round.)
In the past few days I have been doing quite a bit of research on this, and I think for this (my second tube project) I'll go with more of a hi-fi design.
This gent from his university class seems to have nailed down a good design, analytically, and posted good specs and how-to on the parts and so forth. He also did a few mods, like precision resistors, etc., though it's originally from the 1959 RCA tube manual.
I'm just going to use 5% tol. ones of the correct wattage.
http://www.du.edu/~etuttle/electron/elect35.htm
I've scoped out all the parts and sources for them,
and based on his description, I'm pretty sure I can put together a power supply based on a Hammond 325-0-325 trafo, and 8H choke.
It should be interesting, as I mentioned before I got a 6V6 P-P Radio Craftsmen RC-2 monoblock off ebay, and on further inspection I see that it was majorly modified and done badly, and a lot of the resitors are out of spec (this is over 55 yrs old), but the tubes and trafos are fine, just the little stuff has to go.
We'll see how they compare in the long run, performance-wise, once I test them side by side.
Incidentally the main Mallory can cap (60uF 400v / 40uF 400v) seems to test ok, and I've read that some folks using the RC-2 are still running them on the original caps. What makes these last so long? On the other hand if they aren't trustworthy in the long run, why should I ever consider NOS can caps made years ago, even if not used, they are just as risky, no? Just use new radials under the box instead may be the best choice.
This gent from his university class seems to have nailed down a good design, analytically, and posted good specs and how-to on the parts and so forth. He also did a few mods, like precision resistors, etc., though it's originally from the 1959 RCA tube manual.
I'm just going to use 5% tol. ones of the correct wattage.
http://www.du.edu/~etuttle/electron/elect35.htm
An externally hosted image should be here but it was not working when we last tested it.
I've scoped out all the parts and sources for them,
and based on his description, I'm pretty sure I can put together a power supply based on a Hammond 325-0-325 trafo, and 8H choke.
It should be interesting, as I mentioned before I got a 6V6 P-P Radio Craftsmen RC-2 monoblock off ebay, and on further inspection I see that it was majorly modified and done badly, and a lot of the resitors are out of spec (this is over 55 yrs old), but the tubes and trafos are fine, just the little stuff has to go.
We'll see how they compare in the long run, performance-wise, once I test them side by side.
Incidentally the main Mallory can cap (60uF 400v / 40uF 400v) seems to test ok, and I've read that some folks using the RC-2 are still running them on the original caps. What makes these last so long? On the other hand if they aren't trustworthy in the long run, why should I ever consider NOS can caps made years ago, even if not used, they are just as risky, no? Just use new radials under the box instead may be the best choice.
Pointdexter's Music Machine is a very nice 6V6 PP amp...
http://www.audiotropic.net/Projects/machine1.html
http://www.audiotropic.net/Projects/machine1.html
Hang on Frank, I though you wanted to build a guitar amp?? Or have you decided to build a hifi instead? Hifi designs just aren't great for guitar. They use a lot of unecessary components and end up sounding BORING with guitar! Guitar amps are a lot easier to build too (althoug harder to get sounding just right) because they don't need high quality components and don't need to be matched or even have well filtered PSUs.
The guitar is after all, a pretty lame sounding instrument until you add some non-linear amplification and tone adjustments.
By the way, if you haven't already see it; head over to www.ax84.com It's all about building valve guitar amps and they have the best forum on the web for it.
Incidentally I'm building a PP 6V6 guitar amp myself at the moment (of my own design of course!)
The guitar is after all, a pretty lame sounding instrument until you add some non-linear amplification and tone adjustments.
By the way, if you haven't already see it; head over to www.ax84.com It's all about building valve guitar amps and they have the best forum on the web for it.
Incidentally I'm building a PP 6V6 guitar amp myself at the moment (of my own design of course!)
Hi Frank,
this one has an interstage transformer and sounds great (hear the audio file).
http://www.psg.com/~dlamkins/Articles/amp-1-build-narrative.php?cat=amps
Maybe a bit late though. Anyway i still don't know if you waNt a guitar amp or not. For HI-FI i use the poindexter 6v6 PP. Very good amp.
this one has an interstage transformer and sounds great (hear the audio file).
http://www.psg.com/~dlamkins/Articles/amp-1-build-narrative.php?cat=amps
Maybe a bit late though. Anyway i still don't know if you waNt a guitar amp or not. For HI-FI i use the poindexter 6v6 PP. Very good amp.
The 15k resistor is almost entirely irrelevant for that tube's DC operating point, being in parallel with the transformer primary which evidently has a DC resistance a lot less than that. Consider that 12AX7 section is drawing about 2.5ma Ip (to put the cathode 1.2v above ground); while the drop across that 15k | transformer primary is only 4 volts.
Pretty clearly the 15k resistor is being used for some tone shaping, bandwidth being a problem with interstage transformer coupling. It is true that section is running at higher plate current than you usually see for a 12AX7, but that lowers its plate resistance a bit, which also helps frequency response at the low end.
And after all the plate current is really not terribly high. 2.5ma at 250v is only .625w, half the 12AX7's maximum rating per section.
I think it would be an interesting circuit to build. And then build a similar amp with a tube phase splitter (say a Fender Deluxe 5E3)
and compare...
--Paul
Thanks to all of you, and regarding the last 3 replies, I appreciate the further feedback on the resistor across the primary of the interstage transformer, that helps explain it a bit.
I do want to build this guitar amp, and I do have a couple pieces of iron for it, thanks to T. Bavis, but I'm going to play with a hi-fi version at first, so I decided on that 1959 hi-fi version as modified by the professor on that site. I aslo have a Radio Craftsmen RC-2 which I will rebuild (replace all the parts except the the tubes & iron).
The 3.5 watt Fred Nachbauer minblock was my last project, but it needs a preamp, and I'm working on a pre-amp now, to see how the sound ends up quality-wise with that. Then when I get these 2 hi-fi 6V6 P-P amps going, I'm going to compare them very closely, perhaps if they both do well, I'll use both, one for each channel of my stereo, then sell my solid state clunkers from the 70's on ebay.
Then I'll either do the guitar amp project with the 6V6's and the interstage, as I really like the look of the design and simplicity.
I'm going to look at some chassis designs as well, besides the straight aluminum boxes, I'm looking into a gold anodized aluminum plate set into a wooden frame made with moldings, some use of plexiglass perhaps, and maybe some radiator grill metal for enclosing the trafos, etc., as I've seen some real nice work, both here and elsewhere using these ideas...
I do want to build this guitar amp, and I do have a couple pieces of iron for it, thanks to T. Bavis, but I'm going to play with a hi-fi version at first, so I decided on that 1959 hi-fi version as modified by the professor on that site. I aslo have a Radio Craftsmen RC-2 which I will rebuild (replace all the parts except the the tubes & iron).
The 3.5 watt Fred Nachbauer minblock was my last project, but it needs a preamp, and I'm working on a pre-amp now, to see how the sound ends up quality-wise with that. Then when I get these 2 hi-fi 6V6 P-P amps going, I'm going to compare them very closely, perhaps if they both do well, I'll use both, one for each channel of my stereo, then sell my solid state clunkers from the 70's on ebay.
Then I'll either do the guitar amp project with the 6V6's and the interstage, as I really like the look of the design and simplicity.
I'm going to look at some chassis designs as well, besides the straight aluminum boxes, I'm looking into a gold anodized aluminum plate set into a wooden frame made with moldings, some use of plexiglass perhaps, and maybe some radiator grill metal for enclosing the trafos, etc., as I've seen some real nice work, both here and elsewhere using these ideas...
That's a great series of projects you have lined up.
I hope you do get to doing the comparison between your Fender Musicmaster and the Deluxe. Something's got to explain why interstage transformers aren't used in any of the best-regarded guitar amps--the cost is in practice not much different between the two.
One of the great unanswered questions of our time...
--Paul
I hope you do get to doing the comparison between your Fender Musicmaster and the Deluxe. Something's got to explain why interstage transformers aren't used in any of the best-regarded guitar amps--the cost is in practice not much different between the two.
One of the great unanswered questions of our time...
--Paul
Wha?! On valve, socket and a few components compared to an interstage? The tranny would be at least three times more expensive- minimum!Garage Amps said:
Not to mention problems with hum susceptibilty, weight, lack of ability to tweak tone and drive levels, phase shift and associated feedback instability...
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