dual valcaster question

[alcoloic]

hi everybody
i build the dual valvecaster using this unverified schematic
http://www.beavisaudio.com/Projects/ValveCaster/twincaster.gif
it work great but the gain control of the second tube has no effect .
does anyone have the same problem ?
thanks

Loïc

[frequencycentral]

I have only built single tube versions. But try unhooking the two stages and see if the second stage gain works as a standalone maybe???

Or maybe the second stage is just so saturated by the first???

[alcoloic]

Or maybe the second stage is just so saturated by the first???

thanks for helping
i was actually asking myself the same question .
i've read a good part of the 29 pages valvecaster thread and i didn't notice anyone talking about it

[Renegadrian]

Yes, I still haven't build a two-valver myself...So...

[ambulancevoice]

hmm, i think dano made a mistake
shouldnt the 1 uf cap on v2a (called v1a on the schematic) go the grid not the plate?

try that, disconnect the 1uf cap on v12 and connect it to the grid
might be why its not working

[frequencycentral]

Yes, looking at the schematic, Alex is right, that cap should go to pin 2. I think the schemo misses out the third triode altogether.

The 100K above the second triode should be connected to 9v too.

[ambulancevoice]

like this

you should probably power it on 12v dc too

[alcoloic]

thanks a million guys it's working now

[wavenator]

good to hear that
btw
how's the twin?
it has a lot of gain?

[alcoloic]

i don't know what you define has a "lot of gain" but to me that's a lot of gain !!!
it's actually a cool sounding distortion when both tube are engaged but it really kill the sustain (high notes fade away in about 2sec)
maybe my second tube is dead ! i used some crappy ehx tubes btw 

[ACS]

Sounds like a bias problem maybe?

[wavenator]

it sucks
2 sec?
change the R3's and R2's to trimmer and try to bias the tube

[alcoloic]

i tried that but with no results .
this is really strange i have a 3pdt to switch the second tube ; when the second tube is engaged i have a cool sounding disto but if strum hard on my guitar all the hiss disappaer and the disto become gated and farty
then i switch off then on and it works again

[frequencycentral]

Can I ask what power you are supplying to the circuit? The power requirement of two tubes would be 300ma plus, assuming your not using the centre tap of the heater, which I think would double this to 600ma.

Personally , I would run what you have built from a 12 volt 500ma regulated wallwart, using the two tube heaters at 12 volt (paralleled) and ignoring the centre taps (pin 9).

[ambulancevoice]

try this
see on the first tube stage, the 1M resistor to ground after the input cap at the grid
well, do the same with the second stage, add a 1M resistor to ground after the 1uf cap

[Renegadrian]

Isn't that just a pull down R?

[snap]

It is called different, but in deed pulls down the grid to ground DC-wise, and also references the gridside of C3 to a fixed potential so it can`t float around wherever the electrons send the floating gate beyond control.
It is absolutely neccessary there.

[ambulancevoice]

Isn't that just a pull down R?

also, its not because pull down resistors (pop removal ones) are always before the input cap and after the output cap, when needed, usually the volume pot acts as a pull down resistor.

[Renegadrian]

'K, learnt something more...So do you think it's mandatory to duplicate that R1 on the second part of the circuit?
Is it meant to be right after C3?

[Jimmy-H]

It is called different, but in deed pulls down the grid to ground DC-wise, and also references the gridside of C3 to a fixed potential so it can`t float around wherever the electrons send the floating gate beyond control.
It is absolutely necessary there.

Yeah you are right about that.
If you look at the pepper shredder schemo, they use 220K resistor right after the capacitor : http://www.tube-town.net/diy/lov/lov02-peppershredder.jpg
And C3(1) doesn't have to be 1uF, it can be a smaller one just like the C1.