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Tube guitar amp experts, chime in!

V

Vegitto

Diamond Member
Hey all you amp experts,

As some of you might've heard, I built a Fender Vibroverb clone last year. This was a very cool experiment for me, as it enabled me to work with all sorts of things I'd never worked with before (high voltage, tubes, rectification etc). But when the project was done, I just wasn't satisfied. The amp produced a very sterile tone, more something you'd use for record amplification.

Hence the birth of my new project (which will be started in a couple of weeks, when I've got all the info I want and need): A Marshall/Fender hybrid. I really like the sound of Fender amps for clean or blues overdrive, but for rock, I'm more a Marshall kind of guy. I will be taking the pre-amp stages of both the Marshall Plexi's (if I can find a schematic, otherwise I'll have to ask a friend of mine to dig in his) and the Fender Vibroverb (which is practically the same as any Fender tube amp anyway), Fender type phase switching with the tubes Marshall uses and a switchable power amp, enabling me to choose between EL34/6L6GC goodness.

As you can see, this will probably take a while, as I've got a whole lot of stuff planned. In the meantime, to entertain you guys:

I'm looking for a double diode tube. I've built a couple of effects pedals, and everytime I read 'overdrive' or 'fuzz', the schematic contains two diodes in antiparallel. I know what they do (sinewave --> square/jigsaw), and I really like this sound. So, I thought, why not integrate this into my amp? With tubes!

My tube amp guru said it wouldn't work and that double diode tubes didn't exist, but I beg to differ. I remember reading a worklog of someone doing just this exact thing, except in a pedal.

So, ATOT experts, my questions to you:
-What are some double diode tube types? Filament voltage etc. don't really matter right now, as I don't know the best place to implement this yet.
-Is it possible?

Thanks!
 
Thanks. I found the 6H6G (I'd like a line of tubes all neatly in a row).. Do these exist with a topcap (ie, supplying the voltage with a ceramic cap? All of the tubes I've got now have this, and I'd like one of those just for the looks..

Eli, since you knew a tube type, would you also know if my idea is possible or not? 🙂

EDIT: Whoops, excuse me. I forgot I was using 12AX7's as preamp/reverb drive/phase switching tubes.. A 6H6G or a EB91/6AL5 would look perfect between those beauties.. I've got Siemens, Philips and RCA's.. 😀
 
To clarify me asking if my idea'll work, here's what I'm figuring:

If I put the double diode before the first pre-amp stage, the voltage will be way too small to make the diodes do anything; IE my signal would just flow through untouched.
If I put the double diode after the power amp stage, they'll most certainly burn up, because after this stage there's 60-100W of power.
This would have to be implemented either after the first pre-amp stage (and the question then would be, before or after bass/mid/hi schematic or after) or between the second pre-amp stage and the phase switching stage. The question then is, will the diodes be pushed enough to get me that jigsaw I long for so much?
 
I'm not sure, I just looked through a tube database.. lol..

Don't know if the 6H6 has the diodes in anti-parallel or not.

I'm a novice when it comes to tubes really, but I want to learn.

I'm surprised Colt45's ears aren't burning yet.
 
Originally posted by: Eli
I'm not sure, I just looked through a tube database.. lol..

Don't know if the 6H6 has the diodes in anti-parallel or not.

I'm a novice when it comes to tubes really, but I want to learn.

I'm surprised Colt45's ears aren't burning yet.
Click to expand...

That doesn't really matter, it just depends on how you wire the feet. If you would want them in series, regular parallel or even if you just wanted to use just one, it all depends on wiring. A double diode tube implies that there are two diode tubes in one package. It also means that (for example) diode1cathode is on pin 1, diode2cathode is on pin 2 etc. etc. You can just select what you want to use.

That's why Fender uses only 1/2 12AX7 for reverb drive IIRC. The other half is used for regular amplification (and if they don't, they could 😉).
 
Originally posted by: Vegitto

That doesn't really matter, it just depends on how you wire the feet. If you would want them in series, regular parallel or even if you just wanted to use just one, it all depends on wiring. A double diode tube implies that there are two diode tubes in one package. It also means that (for example) diode1cathode is on pin 1, diode2cathode is on pin 2 etc. etc. You can just select what you want to use.

That's why Fender uses only 1/2 12AX7 for reverb drive IIRC. The other half is used for regular amplification (and if they don't, they could 😉).
Click to expand...
Ahh, I see.. duh.

Well, if it doesn't work.. you could always just use two single diode tubes, no?

 
Originally posted by: Eli
Originally posted by: Vegitto

That doesn't really matter, it just depends on how you wire the feet. If you would want them in series, regular parallel or even if you just wanted to use just one, it all depends on wiring. A double diode tube implies that there are two diode tubes in one package. It also means that (for example) diode1cathode is on pin 1, diode2cathode is on pin 2 etc. etc. You can just select what you want to use.

That's why Fender uses only 1/2 12AX7 for reverb drive IIRC. The other half is used for regular amplification (and if they don't, they could 😉).
Click to expand...
Ahh, I see.. duh.

Well, if it doesn't work.. you could always just use two single diode tubes, no?
Click to expand...

Well, no. That's the problem. I want to use a tube diode, and if a double diode doesn't work, two single diodes won't either. My dilemma is that I don't know if I have to drive these diodes, and if I have to, by how much. If you've never built an effects pedal, try and do something like this, it's really easy and customizable, too!

Input --> two diodes in antiparallel --> output. It's crude, and pro's use transistors or FETS to achieve the same thing (I believe Ibanez' famous contraption (the TS-9/TS-808) uses both transistors and antiparallel diodes), but it works.

I want to do the same thing with tube diodes, because of their frequency response. It's way better than silicium/germanium diodes. However, if the input signal isn't big enough, everything just passes straight through and nothing happens. If the input signal is too big, they'll blow. I have to find out where the sweet spot is.
 
What you want to create is asymmetrical clipping.. that is the top half of the sine wave is clipped so hard that it squares out while the bottom is soft clipped and rounded out. That will combine the heavy buzzy fuzz tone you want with the tube like sweetness full of 2nd/3rd/4th order harmonic overtones.

As far as doing this with vacuum tubes.. seems kind of unnecessary in my opinion, but don't let that stop you from doing it.
You may be able to accomplish this with a double diode triode tube but that sort of thing is above my knowledge of tube amplifiers.

As far as building this amp.. the first Marshall (JTM45) was essentially just a ripped off Fender Bassman circuit with a few tweaks (I'm sure you can find out exactly what's different) so perhaps you can use this to your advantage. I think building two switchable preamps and poweramps is again very excessive and how it will even work electronically remains to be seen but again don't let that stop you.
 
My opinion is that you're missing the point. The double diode circuit is used in solid state designs to somewhat emulate tube sound at high gain settings, causing a distortion effect. Unfortunately, the diode circuit is an approximation, and doesn't really emulate tubes, as they clip with harsher edges than tubes do. But many like yourself, actually like that type of harshness in their sound, and have gravitated to that circuit. Doing that with tubes, however may be counterproductive when finished, as they won't give you the edges you desire. A semiconductor diode is a much better rectifier than a tube, especially in the feedback loop of an operational amplifier.

So what you're saying may sound 'sexy' from the viewpoint of a pure tube standpoint, but really doesn't pan out when you analyze the final result that you want. Why not use the solid state distortion circuit with silicon diodes in the preamp stage, and then have tubes everywhere else?
 
Head over to www.ppwatt.com or www.18watt.com. You'll get your answers there. You have to register in order to even lurk, but AFAIK they don't turn anyone down. Make sure and check out the FAQ's, there are TONS of schematics and layouts.

I'm only into Class A tube amps so I can't help you with your specific question, but I guarantee you'll get an answer there.
 
Originally posted by: Vegitto
Hey all you amp experts,

As some of you might've heard, I built a Fender Vibroverb clone last year. This was a very cool experiment for me, as it enabled me to work with all sorts of things I'd never worked with before (high voltage, tubes, rectification etc). But when the project was done, I just wasn't satisfied. The amp produced a very sterile tone, more something you'd use for record amplification.

Hence the birth of my new project (which will be started in a couple of weeks, when I've got all the info I want and need): A Marshall/Fender hybrid. I really like the sound of Fender amps for clean or blues overdrive, but for rock, I'm more a Marshall kind of guy. I will be taking the pre-amp stages of both the Marshall Plexi's (if I can find a schematic, otherwise I'll have to ask a friend of mine to dig in his) and the Fender Vibroverb (which is practically the same as any Fender tube amp anyway), Fender type phase switching with the tubes Marshall uses and a switchable power amp, enabling me to choose between EL34/6L6GC goodness.

As you can see, this will probably take a while, as I've got a whole lot of stuff planned. In the meantime, to entertain you guys:

I'm looking for a double diode tube. I've built a couple of effects pedals, and everytime I read 'overdrive' or 'fuzz', the schematic contains two diodes in antiparallel. I know what they do (sinewave --> square/jigsaw), and I really like this sound. So, I thought, why not integrate this into my amp? With tubes!

My tube amp guru said it wouldn't work and that double diode tubes didn't exist, but I beg to differ. I remember reading a worklog of someone doing just this exact thing, except in a pedal.

So, ATOT experts, my questions to you:
-What are some double diode tube types? Filament voltage etc. don't really matter right now, as I don't know the best place to implement this yet.
-Is it possible?

Thanks!
Click to expand...

Hey, I forgot to ask, what kind of caps did you use? I forget right now, but I built one amp that took about 100 hours for the caps to burn in and give good distortion. I think it was orange drops, the board told me to leave it on but in standby for a week to burn in the caps. Also, speakers need a good break in period too. I usually pack pillows around the amp and crank it up with something heavy on bass break in the speaker, it really cuts down on the "ice picky" treble. You can also try one of those "beam blockers" from weber amps.

Seriously, try leaving the amp on but in standby for a week or so, some caps needs a while to burn in to get good tone. I was honestly surprised with the results after the burn in. I was really disappointed with the sound of this amp that I built earlier this summer until it was good and broken in.


EDIT: I just remembered, they were Sozo caps, not Orange Drops.
 
Originally posted by: Platypus
What you want to create is asymmetrical clipping.. that is the top half of the sine wave is clipped so hard that it squares out while the bottom is soft clipped and rounded out. That will combine the heavy buzzy fuzz tone you want with the tube like sweetness full of 2nd/3rd/4th order harmonic overtones.

Wow, you're really knowledgable.. I put a pefect sine through two diodes in antiparallel (the easy mod I recommended to Eli) and I just saw a perfect jigsaw.. But it sounds alright on my Fender 212R (which is solid state).. I'm not sure what kind of clipping I want, I'll have to research that..

As far as doing this with vacuum tubes.. seems kind of unnecessary in my opinion, but don't let that stop you from doing it.
You may be able to accomplish this with a double diode triode tube but that sort of thing is above my knowledge of tube amplifiers.

Yeah, but the triode would go unused.. Kind of a waste if you ask me..

As far as building this amp.. the first Marshall (JTM45) was essentially just a ripped off Fender Bassman circuit with a few tweaks (I'm sure you can find out exactly what's different) so perhaps you can use this to your advantage. I think building two switchable preamps and poweramps is again very excessive and how it will even work electronically remains to be seen but again don't let that stop you.

I know, but the Plexi's differ a lot from the Fender Bassman circuit, IIRC..
It's actually quite easy to realise this electronically, it's just quite expensive. Fortunately, my guru has practically everything I need, knowledge and materials.
Click to expand...

Originally posted by: Amoreena
My opinion is that you're missing the point. The double diode circuit is used in solid state designs to somewhat emulate tube sound at high gain settings, causing a distortion effect. Unfortunately, the diode circuit is an approximation, and doesn't really emulate tubes, as they clip with harsher edges than tubes do. But many like yourself, actually like that type of harshness in their sound, and have gravitated to that circuit. Doing that with tubes, however may be counterproductive when finished, as they won't give you the edges you desire. A semiconductor diode is a much better rectifier than a tube, especially in the feedback loop of an operational amplifier.

Actually, my idea was to be able to 'overdrive' at low volumes, without having to use an attenuator ('power soak') or a heavy duty master volume pot.. Those really suck tone if you ask me.

So what you're saying may sound 'sexy' from the viewpoint of a pure tube standpoint, but really doesn't pan out when you analyze the final result that you want. Why not use the solid state distortion circuit with silicon diodes in the preamp stage, and then have tubes everywhere else?

I'm going to research a lot of this and simulate some of my concepts in Multisim.. I'll let you guys know what I find out! Thanks!
Click to expand...

Originally posted by: jemcam
Originally posted by: Vegitto
Hey all you amp experts,

As some of you might've heard, I built a Fender Vibroverb clone last year. This was a very cool experiment for me, as it enabled me to work with all sorts of things I'd never worked with before (high voltage, tubes, rectification etc). But when the project was done, I just wasn't satisfied. The amp produced a very sterile tone, more something you'd use for record amplification.

Hence the birth of my new project (which will be started in a couple of weeks, when I've got all the info I want and need): A Marshall/Fender hybrid. I really like the sound of Fender amps for clean or blues overdrive, but for rock, I'm more a Marshall kind of guy. I will be taking the pre-amp stages of both the Marshall Plexi's (if I can find a schematic, otherwise I'll have to ask a friend of mine to dig in his) and the Fender Vibroverb (which is practically the same as any Fender tube amp anyway), Fender type phase switching with the tubes Marshall uses and a switchable power amp, enabling me to choose between EL34/6L6GC goodness.

As you can see, this will probably take a while, as I've got a whole lot of stuff planned. In the meantime, to entertain you guys:

I'm looking for a double diode tube. I've built a couple of effects pedals, and everytime I read 'overdrive' or 'fuzz', the schematic contains two diodes in antiparallel. I know what they do (sinewave --> square/jigsaw), and I really like this sound. So, I thought, why not integrate this into my amp? With tubes!

My tube amp guru said it wouldn't work and that double diode tubes didn't exist, but I beg to differ. I remember reading a worklog of someone doing just this exact thing, except in a pedal.

So, ATOT experts, my questions to you:
-What are some double diode tube types? Filament voltage etc. don't really matter right now, as I don't know the best place to implement this yet.
-Is it possible?

Thanks!
Click to expand...

Hey, I forgot to ask, what kind of caps did you use? I forget right now, but I built one amp that took about 100 hours for the caps to burn in and give good distortion. I think it was orange drops, the board told me to leave it on but in standby for a week to burn in the caps. Also, speakers need a good break in period too. I usually pack pillows around the amp and crank it up with something heavy on bass break in the speaker, it really cuts down on the "ice picky" treble. You can also try one of those "beam blockers" from weber amps.

I know that burning in caps is kind of needed, but audiophile caps are a bunch of BS.. I'm just using 400V caps, I don't know what brand.. There's no measurable difference between normal caps and high-end caps, at least not that I could find.. The speakers will either come from my 212R (2x 12" Fenders) or I might build a speaker cabinet with a single 12" Celestion speaker...

Seriously, try leaving the amp on but in standby for a week or so, some caps needs a while to burn in to get good tone. I was honestly surprised with the results after the burn in. I was really disappointed with the sound of this amp that I built earlier this summer until it was good and broken in.

I'll try that. Burning in an amp usually improves the sound somewhat, but I've used my first build for about 6-8 months heavily, and I still wasn't satisfied. I drew my conclusions from what I learned from the first build, though.


EDIT: I just remembered, they were Sozo caps, not Orange Drops.
Click to expand...

Thanks everyone, keep the tips 'a comin'! 🙂
 
Just to simpliy, why don't you build a Marshall and a Fender clone, but them in the same case, and connect a toggle switch? 😀
 
Originally posted by: Fritzo
Just to simpliy, why don't you build a Marshall and a Fender clone, but them in the same case, and connect a toggle switch? 😀
Click to expand...

Because that would take out a lot of the fun. Plus, I want to be able to use (for example) a Fender preamp with a Marshall-style power amp, or the other way around. I think I can get a lot of interesting sounds from that. I really like Fender's preamp mid scoop, but Marshall's power amp overdrive.
 
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