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

[Hilli]

Hi Guys,
@Germaniun_Boy: yes, that should be the correct schema. (I hope it  ) Maybe you can experiment with the 100K/220K at the output. At the moment I go directly from the 1M Master pot to the output jack.

@gtudoran: we are very happy, that you develop this project and have share it with us. It would be nice, if you could find a solution to SMPS optimisation. Wish you all the best with your digital projects.

@sst4270: you can use all transistors they are labeled as IRF740. (10A 400V) Such as these. In my last build I used IRF840 without problems. (500V/ 8A). Or other high voltage n-channel mosfets.

Best regards, Bernd

 

[Germanium_Boy]

Hilli, do you simply quit 220k resistor from master volume pot, remaining the bridge to ground? Or do you quit the central lug-ground junction too? Yes, I know... a lot of times I forget the basic things, the rudiments of electronics!

By the way, your chassis layout looks great! I'm designing mine inspiring in your work!

gtudoran: thanks for sharing with us your project, it's really brilliant! Good luck with your new, and digital, ideas!

At last, a question... the BCxxx transistor in the PSU... There isn't trouble about A, B or C series, is it? Thanks again for answering sooo many questions...

[Hilli]

Momentary I go from the pot to output. But I will try the voltage devider combination 100K/220K.
The BC547 is uncritically. "C" has a higher voltage gain. You can use a lot of npn universal transistors, like 2N3904.

Greets

[sst4270]

@ Groovenut and Fair child - where are you guys getting your pcbs made?  They look very professional, not diy home made.
I've used ExpressPCB in the U.S. but I'm looking for another source EU, China, etc... with more affordable prices. I love the solder mask, gold pads, pad printed artwork on your boards.

Any assistance or suggestions from anyone else would be appreciated.
I'm gathering all the parts to build this pedal and would like to not have to etch a board.

Regards,

Steve

PS I simply hate etching my own boards.

[Germanium_Boy]

@Hilli... What is the difference between go with or without the pair 100k/200k as voltage divider? I suppose that with it there will be a drop of volume... I think I'll try both of them... But... If you have any interesting conclusion about it... please... let me know!!

Good luck with the new coil! I hope it hasn't any heating issue... If you have a pair of minutes, paste here the link of the ebay-seller, or of the item... By now, my idea is buying it at Farnell, but it will be very kind to have other choices.

Vielen Dank!

[Hilli]

Hi Germaniun_Boy

I saw this method in many other schematics. I think the reason is that  tube poweramps have high input impedances?
I would like to buy the Farnell inductors, but the shipping costs to Germany are very high. But I will let you know the rest of the (never ending?) coil-story.  

Bitteschön.

[Germanium_Boy]

@Hilli... Maybe I'm a bit stupid, almost I'm feeling that... but what is the PCB that you use in your project? Because, after reading 14 pages, I don't find the same! 

Anyway, I can follow the other PCB with your schematic to put my ideas in order...

[Hilli]

This is the layout I used. And here you can find the same as Vector Graphic. The PCB is 83x74mm.

[vasso123]

Why a Toroidal-Inductor shouldn't be used in the SMPS?

[Hilli]

Why a Toroidal-Inductor shouldn't be used in the SMPS?

I tried several Toroidal-Inductors, they have not worked. You can try it, but watch the IRF740. I have destroyed one.  

[gtudoran]

Told ya! 

[Keeb]

Guys, I'm not sure how to fit this in a 1590BB.
Anyone have a drill template by any chance?

[PetMan]

i got to try the hilli tube clean tone mod (with a voltage divider of course), with a switch dpdt to keep true bypass when i attack a tube amp (pre) and  clean tube when i attack a transistor one!

i made a all new pcb with 3 channels and a real pre footswitch box  a la Mesa MarkIV way ! it get different overdriven tones than my Mark IV !

great diy project here!

[J0K3RX]

i got to try the hilli tube clean tone mod (with a voltage divider of course), with a switch dpdt to keep true bypass when i attack a tube amp (pre) and  clean tube when i attack a transistor one!

i made a all new pcb with 3 channels and a real pre footswitch box  a la Mesa MarkIV way ! it get different overdriven tones than my Mark IV !

great diy project here!

Let's see it!

[Hilli]

Where are the pics? 

[guiseppi]

I'm at the testing stage of a build of this using the older layout I believe (but I edited the track)
Voltages seem to be OK atm with some old valves in and vary from about 80v to 500v.

I built this partly as a test for the smps to see if it could be used in a bigger project with more tubes by simply using a bank of them for the various stages.
Would greatly reduce weight for one, cost for another if the mains transformer needs to be bought.

Anyone know how many milliamps this particular psu can reasonably cope with?
Or how many typical preamp tubes?


My intentions were to build a low wattage SLO Clone, using one or two paralleled 6sn7 as power tubes, with the option to pull one for less power.
The output stage would be pretty much from the AX84 4-4-0 studio project.

Here's a shot of the gtfo at present with black lacquer pcb, hand wound 'chubby' 100uH inductor, a bit dusty

[guiseppi]

Voltages seem to be OK atm with some old valves in and vary from about 80v to 500v.

Sorry. With valves in, the psu can reach about 370V, not 500v!

[Henry89789]

Does anyone know how or if this pedal would work with 12AU7 tubes?   I have about a dozen old RCA and Sylvania 12AU7 tubes have been looking for a two-tube pedal like this to build. Thanks.

[gtudoran]

@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.

#Henry: i don't see any reason why it wouldn't work. Pay attention to the maximum anode voltage (you can ajust output voltage with the trimmer); you will not have the same ammount of gain... but i think it would be ok (it's a matter of taste after all and not a matter of not working )

Best regards,
Gabriel Tudoran
Analog Sound

[Henry89789]

gtudoran:  Thanks for the reply.  I have been on that other very long thread about the tube pedals, (looking for a verified schematic of a two tube pedal to build) as well as this one, and I have gotten confused on both threads because it seems that too often someone will post a schematic and then a few posts later will say there was a mistake on the schematic and that it needs to be revised but not post the revised schematic. I am not an electronic engineer but I can build a pedal with a good schematic. Would you please post (not just for me but for everyone who may be similarly confused) a final verified schematic of the two tube pedal. Thanks.