Tube boost + overdrive running off a 9 volt battery

[tonedoggie]

I would also like to know where to get the cool aluminum knobs like the ones in the pictures posted by tipetu recently

[kurtlives]

Smallbear electronics

[tonedoggie]

 - Chris M

thanks for pointing me to Small Bear Electronics - I sent off my order tonight. 

Last thing to buy are a couple of tubes.  I found some really cool vintage 12au7 tubes at audiotubes.com that I am considering ordering, but am a little confused about heater voltage and tube life.  I've read many of the posts here and I can't quite figure out if I should use 12VDC or 9VDC

[kurtlives]

12V DC is what you need. Make sure it is regulated and filtered.

[runmikeyrun]

I haven't read all 75 pages of this, so i am wondering if anyone has build a TRIPLEcaster...?  Or even a Quadcaster... I am considering it.  I should run my valvy into my twincaster to see how it sounds. 

[runmikeyrun]

Hey guys, while i'm a bass player using a valvecaster on bass, just thought i'd clue you in on a little thing i learned tonight @ practice.  Try inserting your valvecaster in your amp's effects loop, if it has one.  I found mine adds a nice extra stage of saturation without getting muddy and ugly.  Try it, you might like!  I use a peavey Windsor and the valvy sounds awesome in the loop.  I'm afraid to try the twincaster i made!!

Would that just be from the line level of the fx loop?

yeah, my amp has a preamp control that drives the fx loop, so the more i crank the preamp the more signal gets to the valvy and the harder it's driven.  if you have a preamp control (pre-gain, etc) you should have some control over it.  Then you control how much signal is getting to the poweramp using the valvy's volume control.  Just be sure not to overdrive the poweramp with it, the volume should be the same with the valvy on and off.

[GeToChKn]

Well I built mine on a proto-board tonight.  I found a tube at my electronics store but they didn't have a socket so I solder 8 wires right to the tube and harvested all the cap's out of dead components.  Its running at 12v but getting a small hum and hiss, so I'm looking to get a 12v regulator tomorrow but I always like to salvage if possible.  I have a small practice amp that I gutted for parts, and it has a small transformer in it but it outputs 12v AC, not DC.  What is required to change AC to DC?  Is it worth it?  I just want to try and use whatever I have laying around that I can.  lol.  Also for pots, all I have a 100k B type pot, a 500k pot from a humbucker guitar and 250k pot from my strat and 10K-B pot from my practice amp.  Which one would be best for the gain control?

[tonedoggie]

I am building my first valvecaster using the schematic on page 1 by dano/beavisaudio.com and have a question about the placement of C3 & C4.  The schematic shows C3 connected from pin 6 of the 12AU7 to to lug 3 of VR3 with C4 connected between lug 3 of VR3 and to lug 3 of VR2.  However, according to the pcb-less wiring diagram also by dano/beavisaudio.com, C3 is connected from pin 6 of the 12AU7 to lug 3 of VR2 and also to lug 3 of VR3 and C4 is connected from lug 2 of VR2 to ground.  I found one post that said "Lug 3 of tone pot in jumpered to lug3 of volume pot just because the author inverted the order of tone pot & cap, with no remarkable differences".   I am interested in any feedback anyone may have on this.

[frequencycentral]

^
^
Either way is fine, won't make any difference.

[letterbeacon]

I'm still having problems with my Valvecaster. I have a feeling that it might be the tube. Can I confirm that when the tube is plugged in the 12VDC is shorted to ground?

[letterbeacon]

Apologies, I can't seem to find the edit button for the previous post.

What I mean by the previous post is that when I insert the 12AU7 tube into the socket, my DMM says there's continuity between the 12VDC coming into the circuit and the ground.  Is this normal?

I also don't understand why the voltage I measure at Pin 1 is so high (I read 10.42V).  Isn't R2 responsible for the voltage down to around 3V? My R2 measures dead on 220K so I don't understand why the voltage at Pin 1 is so high!

If anyone can shed any light then I would really appreciate it!

[GibsonGM]

Well, your DMM may just call the low resistance between pins 4 and 5 'continuity'. Like a light bulb, the heater doesn't have a lot of resistance.  Try reading that with the ohmmeter and see if you get some low resistance. 

I haven't built the Valvecaster, but have it on LT Spice as a simulation....I get close to 7V at the plate of V1, so you are probably in the ballpark. If you are reading w/no tube in the socket, don't forget that the tube's resistance (Rp) must also figure in when thinking about what the voltage there will be. Don't worry, you can't hurt it!!!!!  It's rated for like 350V  ;o)    It all depends on Rp and the cathode resistance...

[letterbeacon]

Well, your DMM may just call the low resistance between pins 4 and 5 'continuity'. Like a light bulb, the heater doesn't have a lot of resistance.  Try reading that with the ohmmeter and see if you get some low resistance.

Yes you're right, I measure 11 ohms between pins 4 and 5.

I haven't built the Valvecaster, but have it on LT Spice as a simulation....I get close to 7V at the plate of V1, so you are probably in the ballpark. If you are reading w/no tube in the socket, don't forget that the tube's resistance (Rp) must also figure in when thinking about what the voltage there will be. Don't worry, you can't hurt it!!!!!  It's rated for like 350V  ;o)    It all depends on Rp and the cathode resistance...

I don't seem to get any overdrive or distortion with my Valvecaster, it just acts like a boost and makes the signal slightly louder.  This is my first tube project so I don't fully 100% understand the circuit -which components do you think I should be looking at?

[GibsonGM]

I actually think you're only supposed to get the very Slightest overdrive from the circuit, if I am reading it correctly...the supply voltage doesn't seem high enough to push the 'AU7 into grid current limiting or cutoff, but to slightly 'round over' your signal.   This would be great going into a tube amp - it would take the place of the input section, and then drive THAT harder (like a REAL TUBE SCREAMER, if you get the drift).  Then the output from amplifier stage 1 is higher, and so on, leading to more distortion in the amp....cascading gain stages.   

You basically have a 1V P-P signal going in from guitar, and you get out about 7V...not bad, a transistor can do this too but not as "warmly" as a tube.  You are, I'm sure, getting SOME distortion and 2nd order harmonics from the tube, also.   A transistor would add 3d, 5th harmonics, which are fuzzy and brittle.   What do you need to look at - what is going on that you don't care for?
 
For more info on basic tube operation, check out http://www.freewebs.com/valvewizard/index.html
This guy, the Valve Wizard, IS a wizard.  Read up on 'triode gain stage'.  To see what's happening with your circuit, you'd need to plot a load line for the 'AU7 at that voltage (very low!) and check out what different anode resistors could do for you.  Also, whether to add a bypass cap or not.....I bought the dude's book, it is AWESOME!!  The supply is so low here, we're lucky to just be getting a boost out of it, which is what it really is!

[GibsonGM]

PS - I did some math, and the 12AU7 running at this voltage and anode resistance gives a gain of about....18. With gain pot set to about 10 ohms.  So, it will clip up to the supply voltage level as it sags - expect an output less than that, of course.  This indicates maybe a little dirt there due to insufficient drive, but not 'distortion'.   Maybe changing the 220k on V1 to 470k or so might improve gain, but I don't think so, it's running so that it barely even indicates being alive on the load line, ha ha!

A 2nd avenue would be to bypass the cathode gain pot with a capacitor...maybe 47nF or so; this will give you a little 'treble boost' and make it seem brighter/clipped more on the high end.   Better described on the site I linked above.   Let us know how you make out!

[letterbeacon]

Thanks for the info - I'm definitely going to check out the Valve Wizard website.

I thought this circuit was a low voltage tube distortion pedal, not just a tube boost.  This YouTube video of the pedal seems to have distortion in it and I used his layout to build mine: http://www.youtube.com/watch?v=3cMqYlhSQ8c.  Maybe I've completely misunderstood this circuit completely!

[REGNAD]

yeah the youtube videos are misleading. i too built mine to those specs. definatly not an overdrive. more like a boost with very mild tube breakup. the videos are either putting a distortion pedal after the valvecaster or using the valvecaster to overdrive the input on the amp. im pretty happy with mine, i would have preferred more breakup but my butler tubedriver takes care of that...

[BigBadDom]

Hi,
Just finished mine today after replacing a tube with o/c heater!  Mine sounds just as GibsonGM and others describe - warms the signal up very nicely but no real distortion.  There's bags of boost - my volume is less than half way, but gain is max.  Driving mine with 12v - no hum issues.  I'm very impressed with the sound from such a simple circuit.  Warms up the front end of my solid state amp perfectly!

Dom

[GibsonGM]

Cool, Dom.  Definitely a good idea to run it at 12V if you have an extra supply or don't mind another power cord - you get that much more headroom.

  A tube amp will break up a lot if you increase the input signal it's expecting to see from 1 or 2V from the pickups, to 7 or 8 from the Valvecaster.  This can = a lot of gain at the front end, and totally overdrive your input!!  Think of solos by Stevie Ray and others...

[letterbeacon]

I turned the Gain all the way up and there is some overdrive there, so it does work after all!  I've spent most of my day reading that Valve Wizard site - definitely going to pick up the book I think.

Are there any DIY tube distortion pedals around?  I'd imagine they'd probably need a DIY power supply to go with them, but I don't mind building one of those as well.