GTFO - Full tube high-gain pedal (2x 12AX7)

[guiseppi]

@giuseppi: 370V is a very nice voltage :> i would recommand you not to go over. You will have to change the FET if you would like to go over that voltage.

I used an IRF840 as that's what I had (I think it will handle at least 500V)
The inductor does get unnervingly hot though...

[hangingmonkey]

can someone signpost me to where i can get 6mm resistors.  Ive looked on google but no luck

[hangingmonkey]

Ok, heres mine:







Im running at 250V and when I crank the gain up to 8 or above, i get a load of high pitched whining.  Im hoping that once I box it and use shielded wires for the in and out then hopefully that might cure it.  Any suggestions?

[golfgti33]

 

[quad]

Is GTFO capable of crunch tones? Judging by demos it does heavier stuff quite well, but what happens if you turn up the drive pot just a little bit? I'm in the process of building one. Just finished drilling the board.
https://www.dropbox.com/s/xkd9gt677xmry88/IMG_0861.JPG

My recent effort was a BK butler tube driver (baja version), which sounds good, but it's a starved plate pedal and not all tube. I made a different layout and separated the power supply from the rest of the board. If anyone wants the layout - PM me.
https://www.dropbox.com/s/s4nvi4rsqv9hjyp/IMG_0613.JPG

[quad]

To answer my own question - it certainly is. I do have one problem though. The volume pot (500KA) doesn't completely kill the volume when turned all the way down. The only change in the circuit is 500KA - as a drive pot, instead of 1Meg, for now. No spare 1Meg's.
https://www.dropbox.com/s/acixo0r0m3b4j9l/847.JPG?m

[tubegeek]

The volume pot (500KA) doesn't completely kill the volume when turned all the way down.

Some pots will have a small resistance at the end of the track that remains, even when the control is all the way down. Some won't (manufacturing tolerances.) In this case, your "offness" will not be total.

Assuming you wired it right, another identical spec pot *may* not behave this way (manufacturing tolerances.)

To see what to expect, measure the resistance between the wiper and the counterclockwise lug with an ohmmeter - if it is 0 or very very low you won't have this problem.

Now, of course, I'd like to ask a question - is this actually a problem? When is "total offness" used on a guitar effect?

[quad]

Some pots will have a small resistance at the end of the track that remains, even when the control is all the way down. Some won't (manufacturing tolerances.) In this case, your "offness" will not be total.

Assuming you wired it right, another identical spec pot *may* not behave this way (manufacturing tolerances.)

To see what to expect, measure the resistance between the wiper and the counterclockwise lug with an ohmmeter - if it is 0 or very very low you won't have this problem.

Now, of course, I'd like to ask a question - is this actually a problem? When is "total offness" used on a guitar effect?

I thought about that. To me it's a second 500KA in a row that doesn't work right. Could be a bad batch. I had another one that was crackling and shorting out somehow. I'm just going to measure the pot. Actually it is a bit of a problem, considering it's still a fairly loud setting at total roll off.  

[tubegeek]

OK, I just looked at the schematic. When POT3 is all the way down, and if the value of the pot is 500K, the situation is like this (I think):

the 10K resistor (R16) and the series combination of the 220K and 10K (R18 and R 17) are in parallel. This parallel combination of 10K and 230K is about 9.6K.

This makes a voltage divider with 500K on top and 9.6K on the bottom, which lets 1.2 % of the signal go into the 220K/10K voltage divider. That divider lets 4.3% of the 1.2% go out the output jack, which is about .05% of the full signal. So for 1V of signal coming off the plate of the tube, you'd have .0005 V - half a millivolt - at the output.

In dB terms, that's -65 dB compared to the full signal, which is pretty far below. And the tone pot POT4 actually reduces the amount of the signal coming out the jack a little more (depending on frequency and where the pot is set.)

If you are getting much signal out the output, you may have it wired incorrectly, 65 dB is a pretty deep cut. However, it is true that that circuit wired correctly will only cut the signal completely if the tone pot POT4 is also all the way down too - that would ground the output jack for AC.

[quad]

Okay, here's my effort. I bought the stuff for valve guards in a hardware store. Professional built ones are nice, but not necessary. Something else to note: you might want to look for a beefier inductor. The one I'm using right now is rated for 2.1A and 85C(max) operation. Gets too hot!
https://www.dropbox.com/s/vyokikutolo1jxu/IMG_08966.png
https://www.dropbox.com/s/hglyzgaj64lc1h5/IMG_0936.JPG?m
https://www.dropbox.com/s/afccu1m0dtprvps/IMG_0937.JPG?m
https://www.dropbox.com/s/1rk5qhz0i30zqz8/IMG_0941.JPG?m
https://www.dropbox.com/s/ygcp8bxovzawbn9/IMG_0943.JPG?m
https://www.dropbox.com/s/niamu4uoka5e69f/IMG_0949.JPG?m

[psychedelicfish]

Looks nice! You've done a good job on those tube guards, I could easily mistake those for professional ones.
My experience with boost converters like the one found in this pedal is that the inductor does get quite warm even with a 5 amp one

[quad]

Looks nice! You've done a good job on those tube guards, I could easily mistake those for professional ones.
My experience with boost converters like the one found in this pedal is that the inductor does get quite warm even with a 5 amp one

Thanks! I'm about to install a 5A inductor, except not a toroidal one, as displayed in that picture. Here's a quote from this thread:

I had the same problem first, the IRF was overheated and destroyed in a very short time. The reason was that I used a toroidal inductor. They are unsuitable for this project.
Please upload pictures.

I was wondering what the reason is? Why do they behave in this circuit the way they do?

[Uriziel]

I have a question, maybe stupid one. Actally bunch of stupid questions.

Is there a particular reason for electrolytics in C11 (psu), C1, C2, C12 and C13. Ref des's are based on Hilli's redrawn sch from post #243. all these values with those voltage ratings are realistical for ceramic caps aswell.

Also, would an amz tonestack work?

Can the mosfet heatsink be connected to the chasis or ground plane, or is it electrically connected to some potential and needs to be floating. (sry havent gone through the datasheet for that particular mosfet yet)

This will definitely be my next build. I've been searching so long for something with tubes.

Somebody above was concerned that the vol won't go all the way down. Everything i've heard about that pedal is that you really don't want to dial down. Besides, when ever do you dial vol all the way down on any of your pedals. I understand that it's a matter of principle but also all pedals are made to be heard and there is no real purpose for muting a pedal, imho.

Also has anyone measured the "ambient" temp of that pedal when it has been working for some time. I recon it will be hot in there but how hot. Partly this question relates to my first question about electrolytics since their lifespan is directly affected by temperature.

Can i switch between different value caps for the first cathode bypass with lets say spdt. I mean would the different value caps have a result or would they or switching itself hurt the tube in V1. I dont have much exp with tubes so thats why all those stupid questions

[fagnermonteiro]

Hi, i saw this post and I was willing to make this pedal. I tried to make the design to fit in a 1590BB box. I wonder if anyone can find fault in this project onboard. I'm a little unsure because this will be my first pedal Valved. My main questions are:

1 - The trails are too thin to work with high voltage? There is a minimum thickness for this?
2 - The connections that I added to get onboard are correct? I refer to the 3pdt switch and jacks.

Can i carry out the project, or have to make any changes?

PS.: Sorry for my english. I'm use google translator to help me

[amptramp]

I'm getting a little lost in the filament wiring here - is pin 4 supposed to be at ground?  If so, pin 9 being open is correct.

I wouldn't worry too much about anything other than the filament for power because it has to take 300 mA into the board.  The problem with high voltage is not the size of the conductors (which only take a few milliamps) but the spacing between the conductors and the ground plane.  I would also eliminate any floating areas like the one beside pin 6 on the left hand tube.  Just looking at your question 1 at the moment.

[fagnermonteiro]

Yes amptramp, the pin 4 is on GND and pin 9 is open. I do not quite understand what u mean by "Eliminate any floating areas like the one beside pin 6", I need to remove the ground plane between the conductors under the left tube? Thank you for your attention

[psychedelicfish]

Yes amptramp, the pin 4 is on GND and pin 9 is open. I do not quite understand what u mean by "Eliminate any floating areas like the one beside pin 6", I need to remove the ground plane between the conductors under the left tube? Thank you for your attention

Yes.

[fagnermonteiro]

Already bought and am hoping components arrive to start building. I'll put here the pictures of the process. Thanks

[amptramp]

Yes amptramp, the pin 4 is on GND and pin 9 is open. I do not quite understand what u mean by "Eliminate any floating areas like the one beside pin 6", I need to remove the ground plane between the conductors under the left tube? Thank you for your attention

Look at the left tube to the left of pin 6.  You have a conductor that goes between pins 5 and 6 and below it a conductor from pin 6.  Between them, there appears to be a floating conductor section that is not connected to anything.  This is generally a bad idea as it will charge up to some indeterminate voltage and couple capacitively to other parts of the circuit.  In other words, it is an antenna.  It may not make much difference in this case or it may be significant.

[fagnermonteiro]

Ok .. I redesigned the layout and removed the orphan islands. This should resolve the potential problem, right? It was better this way, amptramp? The credits of the project is in accordance with the rules of the forum? Thanks.