I once found a schematic, that I planned to build and then my computer croaked and I lost all my favorites. It involed a 6AV6 and a 12Ax7, had a master volume, and marshal style tone controls. Nice.
I have a hifi mono amplifier, from the late 50s with a PP 6v6 output.
It's a nice amp. It had a, as luck would have it 6av6 and 12AX7 in the preamp. Could I have gotten any luckier?
Problem is, I now have no schematic. And I cannot find it to save my life. I was going to build a guitar amp out of this thing.
Does anyone have a relatively simple, but good preamp schematic for guitar use that would work with this amp?
I would really like to get cracking on it. This amp had a strange phono section with 8 or 10 different EQ selections. I used the flat setting and plugged right into it. It had way too much gain. I had since begun disassembling the amp, and never drew the schematic because i didnt plan on using it. From the phase inverter to the output trannys, it's intact.
So I just need a decent preamp schematic, preferably with the 6av6/12ax7 lineup.
Thanks if anyone has any ideas.
I have a hifi mono amplifier, from the late 50s with a PP 6v6 output.
It's a nice amp. It had a, as luck would have it 6av6 and 12AX7 in the preamp. Could I have gotten any luckier?
Problem is, I now have no schematic. And I cannot find it to save my life. I was going to build a guitar amp out of this thing.
Does anyone have a relatively simple, but good preamp schematic for guitar use that would work with this amp?
I would really like to get cracking on it. This amp had a strange phono section with 8 or 10 different EQ selections. I used the flat setting and plugged right into it. It had way too much gain. I had since begun disassembling the amp, and never drew the schematic because i didnt plan on using it. From the phase inverter to the output trannys, it's intact.
So I just need a decent preamp schematic, preferably with the 6av6/12ax7 lineup.
Thanks if anyone has any ideas.
Well, I'm not a guru here but built this 6AV6 preamp and it does a fine job for me. Actually it's just what they call a "gain block". And since I had no tone controls I built a Baxandall stack in a small unpowered box which I connected at the end of the preamp with a short RCA jack cable, and then the other end of it into one of my 6V6 hi-fi amps which has no volume or tone control (also works well on one that does have just an input volume control). You could incorporate it at the end of your preamp very easily without a separate box. It surprised me how well it worked.
This particular version of the tone stack was from a site where the author said it works great in guitar amp scenarios as well.
preamp:
tone stack:
Just be sure to put a .022 uF blocking resistor where it says "in" when coming from the output of the pre-amp to the tone stack. Nothing needed at the other end into the next stage.
This particular version of the tone stack was from a site where the author said it works great in guitar amp scenarios as well.
preamp:
tone stack:
An externally hosted image should be here but it was not working when we last tested it.
Just be sure to put a .022 uF blocking resistor where it says "in" when coming from the output of the pre-amp to the tone stack. Nothing needed at the other end into the next stage.
Two things:
1) Is that tone stack suitible for guitar, or is it hifi?
2) By replacing the second 6av6 with a 12ax7, could you insert the tone stack in between the two stages of the 12ax7 to avoid any insertion loss, and have a hotter output?
Keep em coming!
That looks nice and simple though.
I'm trying to avoid modifying the chassis. The one i have is set up for one 6av6, and one 12ax7
Aaron
1) Is that tone stack suitible for guitar, or is it hifi?
2) By replacing the second 6av6 with a 12ax7, could you insert the tone stack in between the two stages of the 12ax7 to avoid any insertion loss, and have a hotter output?
Keep em coming!
That looks nice and simple though.
I'm trying to avoid modifying the chassis. The one i have is set up for one 6av6, and one 12ax7
Aaron
Aaron: I originally did the research and got quite a bit of great help from Ray_Moth on doing this myself, on this thread, which shows the results:
Placement of tone stacks
The tone stack needs to be at a point in the circuit where there is not a high impedance. Then, taking a look at my two-tube 6AV6 circuit you will notice that there is feedback from the second tube to the first, which precludes using the tone stack between these two elements. So I got it to work great at the end, and just before the amp itself, as an unpowered box. If your second tube is a 12AX7, you have to see what the two elements are doing in relation to each other. In many guitar amps the first element of the second tube can be a voltage amp for the first stage, and then the second element a cathode follower, to lower the impedance. Usually the plate of the first is connected the the grid of the second element in this case, and the output taken from the cathode. This would be an excellent place for a tone stack, though you would need a DC blocker cap too as there would be HV coming from the cathode. The DC blocker caps (.022-.1), even if you have more than one in series, seem to be transparent to the signal, in my course of limited experience messing around with these. A good resource would be to check out the old Fender Amp (and others) schematics online and see how they are set up. (drtube.com and hoffmanamps.com) and best:
TDSL Schematic Links
The site where I got the Baxandall stack info is this one:
Amplifier Tone Stacks - monster.party.hat
The way he has the Baxandall configured here is a good compromise that seems to work well for both guitar & hi-fi, in his opinion. I've only tried on hi-fi so far, but I would try it on your app to see. This week I'm working on a guitar amp, but I'm going to use the original Fender tone stack rather than the Baxandall, to be truer to the original.
As far as volume controls go, on all the amps I've built so far, I usually put a pot just after the input jack (usually a 500k or 1meg audio pot) going into the grid of the first tube element, so that the input signal is grounded to zero when turned all the way counterclockwise. There is also an advantage of having a second volume control, which has been used in "mods" of some amps, which they generally call a "master". With this you can run all the pre-amp stages at full or high input signal, right through the tone stack, and then just before the phase splitter stage, use a volume control there to cut down the signal at that point. If you have multiple instruments and inputs, it also lets you leave the "early stage" volume controls alone so as not to mess up the mixing levels. Let me describe one of these that I've seen: Usually (in this case a Fender amp) the wiper of the Treble pot goes through a .02 cap to the next (phase splitter) element (the tone stack output of the Baxandall also comes from this same wiper). Right between this point you can add a "master" volume. Just put a 1 Meg (or 500k) audio pot here, going to ground. You can also put a 470k resistor in series with an SPST switch, with both of these in parallel to the pot to make a "half power" switch.
The Fender "super reverbs" have a "master", and you can also look at schematics of these for a reference.
Here's a quote I found on the web:
"That being said, you really need to decide whether or not a master volume is going to give you what you expect from the amp. Typical master volume circuits would enable you to turn up the front-end pre-amp section of the amp, and reduce the level of the signal being applied to the output stage. In some instances this works just fine, but it really doesn't let the output tubes work hard, and this is where a good bit of the tone of an amp is generated. There are numerous other types of master volume circuits that work differently and sound different than the standard type of master volume used in a Fender, but bear in mind that all of them will attenuate the signal before it reaches the output stage of the amp, so again, the output stage is not being worked hard. If you're interested in checking out these alternative master volume circuits, pick up a copy of "A Desktop Reference of Hip Vintage Guitar Amps" by Gerald Weber. It has a section called "The Trainwreck Pages" by Ken Fischer. There you will find alternate master volume circuits that can be installed in your amp."
Good luck, and I know these are a bunch of other guys here who know a lot more of this than I do, and I'd love to see some comments, as I'm worrking on this type of thing this week myself.
Placement of tone stacks
The tone stack needs to be at a point in the circuit where there is not a high impedance. Then, taking a look at my two-tube 6AV6 circuit you will notice that there is feedback from the second tube to the first, which precludes using the tone stack between these two elements. So I got it to work great at the end, and just before the amp itself, as an unpowered box. If your second tube is a 12AX7, you have to see what the two elements are doing in relation to each other. In many guitar amps the first element of the second tube can be a voltage amp for the first stage, and then the second element a cathode follower, to lower the impedance. Usually the plate of the first is connected the the grid of the second element in this case, and the output taken from the cathode. This would be an excellent place for a tone stack, though you would need a DC blocker cap too as there would be HV coming from the cathode. The DC blocker caps (.022-.1), even if you have more than one in series, seem to be transparent to the signal, in my course of limited experience messing around with these. A good resource would be to check out the old Fender Amp (and others) schematics online and see how they are set up. (drtube.com and hoffmanamps.com) and best:
TDSL Schematic Links
The site where I got the Baxandall stack info is this one:
Amplifier Tone Stacks - monster.party.hat
The way he has the Baxandall configured here is a good compromise that seems to work well for both guitar & hi-fi, in his opinion. I've only tried on hi-fi so far, but I would try it on your app to see. This week I'm working on a guitar amp, but I'm going to use the original Fender tone stack rather than the Baxandall, to be truer to the original.
As far as volume controls go, on all the amps I've built so far, I usually put a pot just after the input jack (usually a 500k or 1meg audio pot) going into the grid of the first tube element, so that the input signal is grounded to zero when turned all the way counterclockwise. There is also an advantage of having a second volume control, which has been used in "mods" of some amps, which they generally call a "master". With this you can run all the pre-amp stages at full or high input signal, right through the tone stack, and then just before the phase splitter stage, use a volume control there to cut down the signal at that point. If you have multiple instruments and inputs, it also lets you leave the "early stage" volume controls alone so as not to mess up the mixing levels. Let me describe one of these that I've seen: Usually (in this case a Fender amp) the wiper of the Treble pot goes through a .02 cap to the next (phase splitter) element (the tone stack output of the Baxandall also comes from this same wiper). Right between this point you can add a "master" volume. Just put a 1 Meg (or 500k) audio pot here, going to ground. You can also put a 470k resistor in series with an SPST switch, with both of these in parallel to the pot to make a "half power" switch.
The Fender "super reverbs" have a "master", and you can also look at schematics of these for a reference.
Here's a quote I found on the web:
"That being said, you really need to decide whether or not a master volume is going to give you what you expect from the amp. Typical master volume circuits would enable you to turn up the front-end pre-amp section of the amp, and reduce the level of the signal being applied to the output stage. In some instances this works just fine, but it really doesn't let the output tubes work hard, and this is where a good bit of the tone of an amp is generated. There are numerous other types of master volume circuits that work differently and sound different than the standard type of master volume used in a Fender, but bear in mind that all of them will attenuate the signal before it reaches the output stage of the amp, so again, the output stage is not being worked hard. If you're interested in checking out these alternative master volume circuits, pick up a copy of "A Desktop Reference of Hip Vintage Guitar Amps" by Gerald Weber. It has a section called "The Trainwreck Pages" by Ken Fischer. There you will find alternate master volume circuits that can be installed in your amp."
Good luck, and I know these are a bunch of other guys here who know a lot more of this than I do, and I'd love to see some comments, as I'm worrking on this type of thing this week myself.
I have looked at lots of Fender amps, I also own many of them. I have several vintage Fender amps from the 60s, and they are fantastic. What I do not have is a Marshall.
The Fenders (with the exception of my little blues jr) do not break up until you crank them. (I don't have any small ones, the weakling of the bunch is a bassman.. which isnt really weak) I would like something with a master volume, so that I can get a nice crunch at a reasonable volume.
So I'm thinking that shouldnt be too hard. I'll probably find some happy medium with the tone stack in order to get a blend of the two sounds (i like the fender sound, and the marshall crunch). Perhaps I'll just have a switch to choose between the two.
Aaron
The Fenders (with the exception of my little blues jr) do not break up until you crank them. (I don't have any small ones, the weakling of the bunch is a bassman.. which isnt really weak) I would like something with a master volume, so that I can get a nice crunch at a reasonable volume.
So I'm thinking that shouldnt be too hard. I'll probably find some happy medium with the tone stack in order to get a blend of the two sounds (i like the fender sound, and the marshall crunch). Perhaps I'll just have a switch to choose between the two.
Aaron
I have done some digging around, and have decided that perhaps a good building block would be the Fender Deluxe Reverb amp.
here is a link to the schematic:
http://www.schematicheaven.com/fenderamps/deluxe_reverb_ab763_schem.pdf
It has the PP 6v6 outputs, which my building block amp has, also.
Assuming I'll only be using one channel, which I will.. This amp simplifies greatly. I'd just use the normal channel.
I was slightly wrong in my original post, I said there was one 6av6, one 12ax7.. i forgot the second 12at7 for the phase inverter stage.
So I am left with one 9 pin socket, and one 7 pin socket in my chassis.
This schematic shows using 1 12ax7 for the preamp, with the tone stack between the two halves. I would like something with a little more gain, perhaps sort of a drive channel. Would I be able to use the 6av6, which I understand is 1/2 of a 12ax7 for added gain? If so, how would I do that successfully, and how would I implement control over it.. I'm assuming some sort of master volume, but where would I put it.
Any ideas?
Aaron
here is a link to the schematic:
http://www.schematicheaven.com/fenderamps/deluxe_reverb_ab763_schem.pdf
It has the PP 6v6 outputs, which my building block amp has, also.
Assuming I'll only be using one channel, which I will.. This amp simplifies greatly. I'd just use the normal channel.
I was slightly wrong in my original post, I said there was one 6av6, one 12ax7.. i forgot the second 12at7 for the phase inverter stage.
So I am left with one 9 pin socket, and one 7 pin socket in my chassis.
This schematic shows using 1 12ax7 for the preamp, with the tone stack between the two halves. I would like something with a little more gain, perhaps sort of a drive channel. Would I be able to use the 6av6, which I understand is 1/2 of a 12ax7 for added gain? If so, how would I do that successfully, and how would I implement control over it.. I'm assuming some sort of master volume, but where would I put it.
Any ideas?
Aaron
My quick guess would be to put the extra stage at the plate of the first tube (shown there as a 7025).
Add a .022 DC blocking cap there (after the 100k resistor) and run it into your new stage's grid. After this cap you can also put in a 100Meg audio pot for an earlier stage volume control.
It already has a "master", which is just after the tone stack.
Add a .022 DC blocking cap there (after the 100k resistor) and run it into your new stage's grid. After this cap you can also put in a 100Meg audio pot for an earlier stage volume control.
It already has a "master", which is just after the tone stack.
Just to clarify... I'm assuming you meant 1 Meg instead of 100Meg... or perhaps you meant 100K.. but 1 Meg makes sense to me.
Later on, in the next day or two, I'll post a modified schematic with the added gain stage.. and I would like to have you go over it before I fire up the soldering iron.
I also noticed that on the same website where I grabbed the schematic from, is the schematic for just the plain Fender Deluxe (minus the reverb). The schematic is cleaner, and I think I'll use that one to modify from. It just has less components.
Down the road if I wanted to add reverb, that would be easy enough to do anyway, or tremolo, etc. I probably wont bother, I have a trem pedal that I seldom use anyway, and I almost never use reverb. Besides that, the chassis I am using has a separate power supply and is very large, ie. it will have to be mounted in the bottom of the cabinet leaving no room for the reverb tank anyway. I plan to run sheilded cable up to the controls.
Having said that, would it make more sense to mount the whole bit into a new chassis more like the stock fender and just use the iron and tubes from the donor amplifier?
Later on, in the next day or two, I'll post a modified schematic with the added gain stage.. and I would like to have you go over it before I fire up the soldering iron.
I also noticed that on the same website where I grabbed the schematic from, is the schematic for just the plain Fender Deluxe (minus the reverb). The schematic is cleaner, and I think I'll use that one to modify from. It just has less components.
Down the road if I wanted to add reverb, that would be easy enough to do anyway, or tremolo, etc. I probably wont bother, I have a trem pedal that I seldom use anyway, and I almost never use reverb. Besides that, the chassis I am using has a separate power supply and is very large, ie. it will have to be mounted in the bottom of the cabinet leaving no room for the reverb tank anyway. I plan to run sheilded cable up to the controls.
Having said that, would it make more sense to mount the whole bit into a new chassis more like the stock fender and just use the iron and tubes from the donor amplifier?
Yes, I did mean 1 Meg (no such thing as a 100Meg pot), I was getting carried away with reading the schematic, and it was way early, before my first cup of coffee. 🙁 After all your brainstorming, if it does seem easier to do in the long run you could use a new chassis, but that's up to you. I find that with any project, the iron, chassis, and power caps are a good half of the cost (unless you use expensive tubes as well). If you do add another tube, why not a 12AX7 instead of a 6AV6, that way you have an extra stage. You could drill out the 7 pin socket on your old chassis and put in a 9 pin there? I find that gutting the components from an old chassis and rewiring it (with all the hardware, trannies & tube sockets in place) takes about 1/3 the time of setting up a new chassis, drilling, etc. If you find a Fender design you like, I'd choose their component values and perhaps line up the stages as you like. From what I've read, Marshall uses a lot of the same "blocks", the uniqueness is generally in the output tubes and feedback. Guitar amp tone stacks are a bit different from hi-fi, as they are focusing more on a certain range rather than the entire audio spectrum. Aside from that, as far as adding a "gain block" or whatever, my impression (and as I said I'm no expert), is that if you add one of these outside of what the guitar amp schematic calls for, as long as it's fairly linear/flat in overall response (even if it's a hi-fi gain block design) it should just give you more power to the next stage and not really mess up the sound (but don't quote me).
There was another thread I was involved with recently, and the person starting the thread mentioned that originally a lot of the Fender amps used a 12AY7 in the first stage, and that they are very expensive. Most of the clones, copies & re-issues all use a 12AX7, more power at the expense of the "original" softer, more colorful sound a bit, so he tried a 12AV7, and it seems to work ok in some cases (same pinouts). I guess it all make a difference to the trained ear, but I would say experiment and see what you find you like...
There was another thread I was involved with recently, and the person starting the thread mentioned that originally a lot of the Fender amps used a 12AY7 in the first stage, and that they are very expensive. Most of the clones, copies & re-issues all use a 12AX7, more power at the expense of the "original" softer, more colorful sound a bit, so he tried a 12AV7, and it seems to work ok in some cases (same pinouts). I guess it all make a difference to the trained ear, but I would say experiment and see what you find you like...
Honestly, I'm a big fan of 12au7s and 12at7s for first stages in fender amps. I was kind of thinking that anyway, add gain with extra stages, and use the tubes with less gain to begin with. I'd rather have an extra tube to get the boost, and overdrive i want, and the sweeter clean sound of the lower powered tubes.
I could be dead wrong about that, but at least to my ear, dropping the 12ax7s out and putting in 12au7s, gives a much sweeter less harsh sound. Theres almost a more "fendery" sound that way.
Oddly enough, and I dont know if it has anything to do with just the tubes I have handy, or the fact that the amps were designed for 12ax7s, but I've never been able to gig with a 12au7. Every one I own is horribly microphonic, and howls like crazy.. all of them are tuned to just about a perfect A.. haha.
So, I think my plan is to build basically the amp in the schematic, with an extra stage.
The marshall schematics confuse me. I can't figure out what's going on in their preamps. All I know is that they get that massive gain sound at low volumes some how, with their master volume setup.
So there must be some way to mix and match the two.
Aaron
I could be dead wrong about that, but at least to my ear, dropping the 12ax7s out and putting in 12au7s, gives a much sweeter less harsh sound. Theres almost a more "fendery" sound that way.
Oddly enough, and I dont know if it has anything to do with just the tubes I have handy, or the fact that the amps were designed for 12ax7s, but I've never been able to gig with a 12au7. Every one I own is horribly microphonic, and howls like crazy.. all of them are tuned to just about a perfect A.. haha.
So, I think my plan is to build basically the amp in the schematic, with an extra stage.
The marshall schematics confuse me. I can't figure out what's going on in their preamps. All I know is that they get that massive gain sound at low volumes some how, with their master volume setup.
So there must be some way to mix and match the two.
Aaron
If this works... here is the schematic!
Let me know if it looks like it will work, and more importantly sound good.
I hope the pic worked.
Aaron
Let me know if it looks like it will work, and more importantly sound good.
I hope the pic worked.
Aaron
Looks pretty linear to me, and I don't see anything missing that would cause a major problem. As long as you are in the ballpark of plate voltages, and have researched the cathode values, etc., I would say give it a shot and see how it sounds.
My one second thought on this is that the tone stacks are designed to work better with a low impedance output, not sure how this will pan out with two straight stages in series. It's better to design the two gain stages with a feedback line (say a 220k resistor from the plate of the second to the cathode of the first), not changing anything else. That would lower the impedance. But then you could not have a volume control between the two.
Also a lot of guitar amps use a voltage amp/cathode follower which is also quite simple.
Also a lot of guitar amps use a voltage amp/cathode follower which is also quite simple.
At this point, that's beyond my expertise. I just try to notice how things fit together, and take in all the opinions I see with linking up this & that (mixing and matching proven stages) and others' observations. I would say, since you did a good setup there, just try it and see how it sounds for you. Then we could do some troubleshooting if you get odd symptoms.
I took apart my blues Jr and ran the preamp direct into the phase splitter of the 6v6 amp. it sounds WOW. It sounds really good. I don't think its loud enough though, so I may just go ahead and start from the drawing board and make myself a nice AC30 clone, which was another idea.
lol. I will probably just build this amp because it sounds good. But then I'll have another amp lying around.
The preamp in the Blues Jr. is a bit on the complicated side.. it has some funky transistor thing going on in the first stage.. I dont know why or what it's for. And it gets muddy when you turn the gain up, slightly. So I dont know.
I have all these parts lying around, I should do something with them. I might just build a stock deluxe clone, and an AC 30. ... OR I'll make a 4 6L6 amp that would be plenty loud... I think i have an OPT that will handle the load.
Aaron
lol. I will probably just build this amp because it sounds good. But then I'll have another amp lying around.
The preamp in the Blues Jr. is a bit on the complicated side.. it has some funky transistor thing going on in the first stage.. I dont know why or what it's for. And it gets muddy when you turn the gain up, slightly. So I dont know.
I have all these parts lying around, I should do something with them. I might just build a stock deluxe clone, and an AC 30. ... OR I'll make a 4 6L6 amp that would be plenty loud... I think i have an OPT that will handle the load.
Aaron
Cool, just post back and I'd enjoy seeing how you do, and hopefully give some good input when I can.
sub away
Using the 6av6 as a sub for the popular 12ax7 is a very practicle way to to go alternate....just wire them in same as each half of a 12ax7 and connect the diodes to the cathode (or not at all).....if the 6av6 (U100) is too strong it can be subbed with a 6at6 (U70).....there are others....6c4 ,similar to half 12au7(different pin out?)...these tubes sub really well,so well that I am making amps with these instead of 12xx7's as they are abundant and cheap and of high quality...I recently bought 6 NEC NOS for $16 ,try buying 3 NOS 12ax7 for that !
the only con with them is in combo's they may be microphonic ...and they use twice the heater current....oddly enough a little microphonics is not always a bad thing....cheers😀
Another note.....the tubes in this amp schem are 6v6.....in place of these you can use 6aq5,6005 and I think there is a Bendix one as well...again cheap NOS gold.....just gotta drop you plate volts to 270v max as they are small 7 pin tubes , same as 6av6, otherwise same as 6v6 in spec.....or the 9 pin 6bw6 can use 315v....I have made these amps and they sound better than Russian tubed commercial amps in my opinion........build on !!!
Notice in the schem above that half of one 12ax7 is not used .....good place for a single triode !
Using the 6av6 as a sub for the popular 12ax7 is a very practicle way to to go alternate....just wire them in same as each half of a 12ax7 and connect the diodes to the cathode (or not at all).....if the 6av6 (U100) is too strong it can be subbed with a 6at6 (U70).....there are others....6c4 ,similar to half 12au7(different pin out?)...these tubes sub really well,so well that I am making amps with these instead of 12xx7's as they are abundant and cheap and of high quality...I recently bought 6 NEC NOS for $16 ,try buying 3 NOS 12ax7 for that !
the only con with them is in combo's they may be microphonic ...and they use twice the heater current....oddly enough a little microphonics is not always a bad thing....cheers😀
Another note.....the tubes in this amp schem are 6v6.....in place of these you can use 6aq5,6005 and I think there is a Bendix one as well...again cheap NOS gold.....just gotta drop you plate volts to 270v max as they are small 7 pin tubes , same as 6av6, otherwise same as 6v6 in spec.....or the 9 pin 6bw6 can use 315v....I have made these amps and they sound better than Russian tubed commercial amps in my opinion........build on !!!
Notice in the schem above that half of one 12ax7 is not used .....good place for a single triode !
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I know that this is an older thread. Do you mean a. 022 uf blocking capacitor? Also does it go after the..1uf cap on the output of the preamp, before the tone stack? Thanks
Kennyg
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No I meant capacitor, the schematic is correct just as posted
The additional .022 would go at the input of the tone stack, sorry the image of that is gone after 10 years, but do a search for Baxandall and maybe you will find it
The additional .022 would go at the input of the tone stack, sorry the image of that is gone after 10 years, but do a search for Baxandall and maybe you will find it
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