Tube boost + overdrive running off a 9 volt battery

[Zben3129]

Just built my 3rd valvecaster. My first one was for me, and the first time I brought it to a rehearsal, my buddy asked me for one. I made him one, and his brother wanted one  .His brother actually offered to pay for it!

Long story short, these things rock!


Quite a thread we got going here aswell. I looked back to my first posts on this thread way back, and I realized this thread is what prompted me into building tube amps. 2 amps and 3 Valvecasters later, I finally feel like I know a thing (maybe 2) about tubes.

Zach

[Zben3129]

Oh, and by the way, I had my friend bring his to a rehearsal, and afterwards, we got it set up with a switch that cuts all the gain directly to clean boost. I brought my meter, and about 50 resistors valued 1ohm to about 15k. We figured out where the maximum clean headroom with his main axe on full volume was, I measured it, and ended up putting in a 12k resistor, and added a stomp switch for clean boost (did I mention I brought my drill aswell  ).

Zach

[andrew_k]

And for what I understood...higher resistance value = more gain?

It would seem that's the case. I'm a newbie too, so I just mess with things until I break it or it sounds cool 

I'm a little concerned about the affect an increased gain would have on tube life. Maybe one of the more experienced guys can chime in here...?

After experimenting with all sorts of boosts before and after, I'm going to box mine up without any extra gain stages (maybe a high impedance buffer at input to retain more sparkle, I'll be testing that on the weekend). If I want more gain I'll just use another boost or OD pedal before or after the tube drive.

[Zben3129]

I'll give about 90% confidence on this one...so don't be mad if im wrong 

I don't believe the added gain will do anything to tube life, at least on a measureable scale. Keep in mind, these things are designed to run more than 10-20 times as much voltage as you are running here. If theres anything that is going to reduce tube life here, it is the fact that you are running them on suck low voltage, which (I believe) causes stripping, and decreases life.

So, unless anyone corrects me otherwise, go ahead. Build a gain monster!

Zach

[Aren]

I added a 7812 regulator, and it now works like a charm!
Makes my acoustic sound half decent when going direct! 

[kurtlives]

Oh, and by the way, I had my friend bring his to a rehearsal, and afterwards, we got it set up with a switch that cuts all the gain directly to clean boost. I brought my meter, and about 50 resistors valued 1ohm to about 15k. We figured out where the maximum clean headroom with his main axe on full volume was, I measured it, and ended up putting in a 12k resistor, and added a stomp switch for clean boost (did I mention I brought my drill aswell  ).

Zach

How did you wire it?

[snoof]

running the heaters at above or below the required voltage will do harm to the tube over time.  I wouldn't use any of your NOS super mojo tubes in this design unless you run the heaters at 12v.(or 6v if using pins 4+5 and 9).

[Zben3129]

Oh, and by the way, I had my friend bring his to a rehearsal, and afterwards, we got it set up with a switch that cuts all the gain directly to clean boost. I brought my meter, and about 50 resistors valued 1ohm to about 15k. We figured out where the maximum clean headroom with his main axe on full volume was, I measured it, and ended up putting in a 12k resistor, and added a stomp switch for clean boost (did I mention I brought my drill aswell  ).

Zach

How did you wire it?

Sorry if this is wrong, I'll go look at the schem in a minute...

but I just used a spdt, pin 3 of 12au7 going to middle lug of switch, one side of switch had pot, the other had the 12k

Zach

[Caferacernoc]

Adding resistance to the plate resistors(R1 and R2) will increase gain. Adding resisitance to VR1, in series with the gain pot, will decrease gain.

[Zben3129]

Hmmm...

I didn't have the schematic with me, all I know is I used a spdt somehow and a 12k resistor.

Maybe it was "after the pot" to the middle lug, one side going to ground and the other to a 12k to ground.



Zach

[Krinor]

For the benefit of Mr. Chawk (and anyone else who wants to build this thing), here are some gut shots of the point to point version of the Valvecaster. Please note that this was done quickly and eagerly, so the soldering is rather crappy. 

[Renegadrian]

NICE SHOTZ!!!

[Chawk]

Fantastic!!! Much thanks!   

[Boogdish]

so the soldering is rather crappy. 

if that's what counts as crappy, then I got a LOTTA catching up to do.

[DryRoasted]

I knocked this up today to have a play with the circuit.  Looking around the net I found a few tube circuits in the same vien and this board is enitirely plug and play to allow maximum tweekage.  Me and her are gonna get real aquanted over the next few weeks   (sorry, hill billy mode)



<edit> Yes I know it shpuld be a glass of JD and coke for the full rock n roll kudos but hey, i'm English

[Krinor]

Now that's nice and clean!
Be sure to post your findings here (once you get to know her).
And I thought englishmen only drank tea ? 

[Renegadrian]

Well, There's the Ruby Tuby, both preamp or full amp - and other sophtamps creations...Sad I suck at reading schematics...
If I only find vero/perf/pcb of any of these...

[Aren]

Hmmpf... I would just replace the opamp stage with a JFET buffer, stick the Valvecaster in front of it, and feed it to a 386 amp.
Seems easier...

[Krinor]

Well, There's the Ruby Tuby, both preamp or full amp - and other sophtamps creations...Sad I suck at reading schematics...
If I only find vero/perf/pcb of any of these...

Surely you are aware of Dano's "Tube Cricket" ? That one seems like a logic progression from the Valvecaster.

[DryRoasted]

First observations from the valvecaster test rig:

Using a 12AX7 at 12V and no tone stack, everything else stock - a bit "wooly" for my liking not alot of note defination, a bit boomy (this is coming from a confirmed metal head).  Change the input cap (C1) to 22nF and its a whole new game.  Lots of ACDC-esque tone, lovely response and works well with humbuckers (no idea about single coil).

Next up, same as above but changed R3 from 100K to 240K and moved VR1 from the leg of tube pin 3 to pin 8 and jumpered pin three to ground - Not a masive change but enough to give a noticable comparison.  Most obvious thing is the response of the gain control VR1, before, most of the control was in the last 1/4 turn but now its more evenly spread.  Overall tone remains useable.