linear Low voltage tube project(pedal)

iccaros · May 20, 2011, 08:13:26 PM

I found this write up on how to use starved plate better than what I have seen. http://www.freewebs.com/valvewizard2/Triodes_at_low_voltages_Blencowe.pdf

So I was wondering if the smart minds on this board could come up with a better design than the valvecaster, but stayed @ 12volts. No voltage doublers. I am not afraid of throwing in a op-amp or something else, but this could be all tube. According to the document it looks like 2nd order harmonics are doable with just a tube design.

So I was thinking.. a pentode in front of a triode @ 12v. so the pentode does the boost into the dual triode. I have two 6au6's I got from a hammond organ I could use..

In any case. I am looking for others smarter than me, to review this and give their two cents.. When I get back Sunday I can start putting this together.

here is an example...

Looks simple.. This should be clean, so that the pentode should be able to overdrive it.. So a 12au7 or some other low or med Mu triode would give a better overdrive, but a 12ax7 should also work.

Thanks

iccaros · May 22, 2011, 10:48:50 PM

ok I tested this.. I works.. but its clean, unlike a valve caster which gets dirty, this stays clean... But way overdrives my input on my amp. I turn it down and get a good clean boost.

so at 12volts the same tube is giving more output than the valve caster @ 30. I am using a 12ax7.. I am really impressed with the output.. its almost like the first stage of a normal high voltage preamp

I think if I drive the pentode with this I should get a good overdrive...
Working on it.. will let you know..

iccaros · May 23, 2011, 02:53:31 AM

ok here is what I got so far.. I can not believe how good this distortion sounds.. The only problem its full on, a way to kill the gain would be good.. Need to play more.. But full on power tube distortion @ 12V

No need for to raise the voltage... Maybe.. but here it is so far
Tubes.. Pentode is a 6au6 and the Dual triode is a 12ax7

Tips and ideals welcome..

Name so far.. Sky Hunter...

Steben · May 23, 2011, 05:20:31 AM

12ax7 has more gain

you could try 12U7 instead of 12AU7, about same gain, but designed for 12V car audio.

triodes en pentodes distort different. Pentodes behave more like fet's. Triodes a bit cleaner / linear (ideal for clean/crunch).

Mike Burgundy · May 23, 2011, 07:26:06 AM

Hey, that's interesting. Starved plate is usually regarded as "charicature" tube sound - very non-linear and squashed. If dynamics are okay, this might be interesting for other starved plate circuits - such as compressors, mic-pres. Starved plate comps and pres usually don't hold up to high voltage ones, I need to find my breadboard and a box of time....
Thanks, good find.

iccaros · May 23, 2011, 09:47:44 AM

Quote from: Steben on May 23, 2011, 05:20:31 AM
12ax7 has more gain

you could try 12U7 instead of 12AU7, about same gain, but designed for 12V car audio.

triodes en pentodes distort different. Pentodes behave more like fet's. Triodes a bit cleaner / linear (ideal for clean/crunch).

Thanks for the suggestions..
In this case the 12au7/12u7 distorts faster and is louder as it is more linear of a tube, but tube rolling is good, I you replace the 690K with what ever gives you about 6 volts for the other tube type or go by ear, I had a 220K and a 1M pot for this, but 640K is what I measured when It sounded best.. If you just have the fist part with the 12ax7 you get zero distortion in this build..
I have tried 12u7, 12au7, 12ae7 and this 12ax7. In truth I kind of want to get a 12AX7 to run well, as with other starved plate you have to get above 30v for this to work.. And it does work well, I just need to turn it down so it makes a useful pedal, right now for me, it would be on or off.. no need for pots
The pentode in starved plate is the one overdriving.. In this design just the pentode overdrives a little. with the 12ax7 it overdrives a lot.. I'll make sound clips tonight.. I have a volume between them, but all the way down the pentode is still overdriving.. I am thinking of putting a resistor in between the two so there is a min about of load. But a resistor on a grid creates distortion to some degree..

iccaros · May 23, 2011, 09:52:33 AM

Quote from: Mike Burgundy on May 23, 2011, 07:26:06 AM
Hey, that's interesting. Starved plate is usually regarded as "charicature" tube sound - very non-linear and squashed. If dynamics are okay, this might be interesting for other starved plate circuits - such as compressors, mic-pres. Starved plate comps and pres usually don't hold up to high voltage ones, I need to find my breadboard and a box of time....
Thanks, good find.

I was very surprised that in this configuration I could not get the 12ax7 or 12u7 and a 12au7 and a 12ae7 to overdrive, they just got louder.. so it worked.... the paper was not BS....
then adding the pentaboost behind it gave full power tube distortion, not the grainy distortion a 12ax7 gives by it's self... and I put this on a clean channel of my amp... @12v (running off a computer ATX power supply I have as bench power.. makes it nice as I can use 5v for the heaters.)

ThunderShowers · May 23, 2011, 05:01:01 PM

Schematic front side side works as Linear Tube Booster on 9-volts stand alone.

Would make a great one knob Volume booster pedal.

EDIT: I used a .047 uf oputput cap, and swapped out the 690k for a 620k r.

iccaros · May 23, 2011, 05:51:29 PM

Quote from: ThunderShowers on May 23, 2011, 05:01:01 PM
Schematic front side side works as Linear Tube Booster on 9-volts stand alone.

Would make a great one knob Volume booster pedal.

EDIT: I used a .047 uf oputput cap, and swapped out the 690k for a 620k r.

I was thinking of putting a bypass so you could switch in the pentode when you want overdrive.. and just have the clean boost..

Did the .047 do anything to tone for you?
and 620k is good, I had a 220k and a 1 meg pot and came away with the closest resistor, I have the 220k and 470K in series right now..

ThunderShowers · May 23, 2011, 06:21:03 PM

Dunno, it's what I had on hand: also stuck a .1 uf Cap at the front so tru-bypass don't pop as loud.

Works better with the 12ax7 then it does with the 5751 I love with the 'Castor.

Sounds warmer way up the neck then just the guitar into the amp (Valve SR.)

Makes a Stock 'Castor sound cooler then hell when you boost into it.

I dunno, I'm just loving it as a Standalone Front of Line Booster.

iccaros · May 23, 2011, 06:48:00 PM

Quote from: ThunderShowers on May 23, 2011, 06:21:03 PM
Dunno, it's what I had on hand: also stuck a .1 uf Cap at the front so tru-bypass don't pop as loud.

Works better with the 12ax7 then it does with the 5751 I love with the 'Castor.

Sounds warmer way up the neck then just the guitar into the amp (Valve SR.)

Makes a Stock 'Castor sound cooler then hell when you boost into it.

I dunno, I'm just loving it as a Standalone Front of Line Booster.

+1 thanks for the feedback, will think on that, IF you have an 12AU7 or by chance a 12U7 I found it gives more or a boost, if you need it? So some reason the Lower Mu tube gave more output.. I did not try a 5751, which I have in my valvecaster @ 30volts.

I am thinking of doing this with a 6112 and a 5840 sub-mini, one button boost, second button over drive.. two volume pots.

I did not put a cap in front as I was thinking 10uf but had no non-polarized caps in that range.. Will go with a .1 good suggestion.. I can not wait for the kids to wake up so I can work on this some more..

iccaros · May 23, 2011, 08:06:54 PM

I am getting lots of low end farting.. Need to trouble shoot.. IT may be the breadboad.. But need to check.

ThunderShowers · May 23, 2011, 08:54:30 PM

Quote from: iccaros on May 23, 2011, 08:06:54 PM
I am getting lots of low end farting.. Need to trouble shoot.. IT may be the breadboad.. But need to check.

Lower your output caps values. 10uf is p. high, so you're going to get tons of bass though.

EDIT: Running guitar, bass and Longhorn Bass (Mid-Range sound heavy), switching between the Booster shown here and a modified 'Castor, both on straight nine V.

With guitar, the Booster is louder. With the longhorn, the 'Castor begins to pickup slack and breaks about even (Fully up on gain and volume) and on the bass, the 'Castor roars out and the Booster stays about the same. Not Quite sure what the heck is going on there, I'm supposing it's a biasing reaction with the input signals strength...

iccaros · May 23, 2011, 09:12:02 PM

Quote from: ThunderShowers on May 23, 2011, 08:54:30 PM
Quote from: iccaros on May 23, 2011, 08:06:54 PM
I am getting lots of low end farting.. Need to trouble shoot.. IT may be the breadboad.. But need to check.

Lower your output caps values. 10uf is p. high, so you're going to get tons of bass though.

EDIT: Running guitar, bass and Longhorn Bass (Mid-Range sound heavy), switching between the Booster shown here and a modified 'Castor, both on straight nine V.

With guitar, the Booster is louder. With the longhorn, the 'Castor begins to pickup slack and breaks about even (Fully up on gain and volume) and on the bass, the 'Castor roars out and the Booster stays about the same. Not Quite sure what the heck is going on there, I'm supposing it's a biasing reaction with the input signals strength...

lowed the caps, sounds much better. my supply is caps from .04 - 1.0 so I used what I had
I updated the schematic..

here is a really bad video but gives an ideal of the overdrive this gives..

Ignore the fat dude talking..

ThunderShowers · May 23, 2011, 09:33:48 PM

Hmmmm, With a pinout change could I get a 6v6 running instead of that 6au6?

Sounds nice as it is though, Just have a spare 6v6 on hand here (My ARC takes them)

iccaros · May 23, 2011, 09:36:01 PM

Quote from: ThunderShowers on May 23, 2011, 08:54:30 PM

EDIT: Running guitar, bass and Longhorn Bass (Mid-Range sound heavy), switching between the Booster shown here and a modified 'Castor, both on straight nine V.

With guitar, the Booster is louder. With the longhorn, the 'Castor begins to pickup slack and breaks about even (Fully up on gain and volume) and on the bass, the 'Castor roars out and the Booster stays about the same. Not Quite sure what the heck is going on there, I'm supposing it's a biasing reaction with the input signals strength...

I have not tried other things in-front of it.. Just the Les Paul
I added a 1m to ground on the input before the cap and seamed to help stabilize the input.. but it could be placebo effect

iccaros · May 23, 2011, 09:41:38 PM

Quote from: ThunderShowers on May 23, 2011, 09:33:48 PM
Hmmmm, With a pinout change could I get a 6v6 running instead of that 6au6?

Sounds nice as it is though, Just have a spare 6v6 on hand here (My ARC takes them)

Let me know.. I don't have a 6v6 to test.. But I do not see why not...
I am looking at a 6112 and 5840 submini.. Fit into a small pedal....

ThunderShowers · May 23, 2011, 09:45:43 PM

Quote from: iccaros on May 23, 2011, 09:36:01 PM
I have not tried other things in-front of it.. Just the Les Paul
I added a 1m to ground on the input before the cap and seamed to help stabilize the input.. but it could be placebo effect

pull down, cap, pull up... That... I, ah...

Now I've got to try it, d@mnit.

Mini can be cool. I'm just trying to stay towards readily available; I have enough trouble getting the 6av6's I need for my ARC. Shipping them in takes forever.

iccaros · May 23, 2011, 09:56:50 PM

I just bought (4) 6112 and (5) 5480 off ebay, they have a lot more.... tempting? ..

ThunderShowers · May 23, 2011, 10:06:41 PM

Quote from: iccaros on May 23, 2011, 09:56:50 PM
I just bought (4) 6112 and (5) 5480 off ebay, they have a lot more.... tempting? ..

Nah.

Just tried again;
The Bass sucked all the power out of the Linear Boost, even with the pulldown resistor. And the 'Castor increased in gain compared to the guitar. With a guitar, the Booster definitely is a winner, but it's not liking my Bass at all (a Dano '63)

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linear Low voltage tube project(pedal)