freestompboxes.org

Hello forum-mates,

All of the tube preamp pedals, booster tube pedals, whatever, use, normally one or two 12ax7's. Now, regarding tube saturation, I prefer the sound of a saturated EL84 to the one of a 12ax7. Now, is it possible to achieve that poweramp saturation in a pedal, using a EL84, or a power amp tube, in general?

i think you would need to build a preamp section anyway to overdrive the output tubes. you could always make the preamp solid state a la musicman to keep the size down, but at that point you might as well buy some trannies and just build a full-sized amp. now that i think about it, you'd need a PT anyway for a power tube (or preamp tube, really) to operate as it would in a full-sized amp. most "starved plate" 12ax7 pedals sound like crap (IMO), and i'm not sure if a power tube will even function with 9-18v on the plate.

i could be wrong though, and it's certainly worth a try if you're up for a challenge. maybe someone with more knowledge than me can give you better info.

There are certain power tubes that are designed to run with 12v on the plate, but they don't sound anything like an EL84. I've experimented with them and gotten decent results - imagine something like a Herzog. But, like a Herzog, it's not something I'd actually do in a "pedal" format. I guess you could use a big box, but still, the tubes will have a longer, happier life if you get them off of the floor and out from under your feet. I think it would be really cool to do an EL84-based thing that's like a Herzog and runs at the proper voltages. Hughes&Kettner already did a similar thing with their Cream Machine recording amps. I'm totally into the idea of doing a thing like that, but it would be in the "it sits on top of your amp" Herzog format, not the stompbox format. Though, I think if you put it in a smallish cabinet, it could probably live on the floor next to your pedalboard. The main thing is that the footswitch would be a separate item, so you're not stomping on the tubes.

I have designed and built many tube distortion pedals using ECC83 / 12AX7 tubes on low volts and on 250v DC.
In my opinion they sound better at higher voltages - the starved plate pedals on 12v DC sound way to mushy to me.
The BK Butler Tube Driver runs his tubes off 24v DC or +12v and -12v to be precise - David Gilmour uses two in his rack (though not at the same time - two effects loops).
Elsewhere on this forum are plans to build a clone if you so desire .
I have built a twin 12AX7 pedal that runs off 250vDC plate supply, loosely based on the BadCat Xtreme tone pedal, but in a much smaller NSC case.
I have sold a few of these to satisfied customers - my design will run off a 24v AC (not DC) adaptor - so can be used anywhere in the World.
I do not like 115AC to 230AC around my feet or other pedals!!!
I intend to put this up as a project one day in the near future, but it is not for the faint hearted or noobie sorry.
Another pedal i built last year uses a 12AX7 to push pull drive a pair of EF86 pentode tubes into a small power transformer as an output transformer - I also included a small 2.5 inch loudspeaker as a load and used a cheap electret element connected through a small passive filter to a line out socket - interesting sounding device - I must tidy it up - been sidetracked with other stuff over the last few months. It to uses a 24vAC adaptor to power it, and runs off real World tube voltages internally.
I may post some pictures later if anyone is interested.
Stay cool folks
bajaman

What about building a small tube amp with "medium" voltage? say 60 to 80V?

And what about this idea?



You can use the ECC83 and EL84 instead ECL86. The creator of the device used it in a fx loop of Marshall Valvestate to get sound of full cranked tube amp at low volume.
Sorry for my poor english.

My simplified view of understanding The Great OD Sound;
First Some Facts:
Pentode's where invented to overcome the shortcomings of Triodes. (Hint)
Triode's can't do square wave even when driving a transformer. (Hint)
Pentodes have far more TC (Trans-conductance) than Tetrode's.
Cathode biased power stages with NO FeedBack will ALWAYS have more comp/OD/Distortion
than Fixed biased amps.

Problem is 9 out of ten players buy a big Fixed biased Amp because they think it's going
to sound bigger/better if it has more wattage,,,then spend the next ten years buying pedals
that reproduces the sound of a cheap crappy Cathode biased Amp via some exotic complex circuit
that requires Unobtainium for it to work. Go figure???

*thereminator* is on the right track winky,,
a simple line out from a basic Valve amp to a bigger Amp and it's heaven.
urr cough! Though I think the schematic may need some voltage on the screen grid.

Also the secondary load needs to be larger and you need some series resistance before
the line-out is taken.

@ *DWBH* I have no doubt someone who is keen will find some good tricks implementing
valve pedals that come close but I don't have a lifetime to wait so I just use simple tricks
Not unlike *thereminator's* idea above.

In general it will make life a lot easier if you use Valves at higher voltage,, at least 90Volts.
Also note that you don't need utterly stupid voltages.
My very basic 7Watt Soaked head only uses 260VDC supply and it's as sweet as.
Some EL84 Amps today have voltages that are way beyond the 300VDC design rules and
the harshness is clearly evident to my ears.
My 2 sense worth,, Phil.

phatt wrote: ...at least 90Volts.

I like that. I'd like to try to build a little tube amp with minimal parts count, less expense, longer tube life, fewer tubes, lower voltage.
I'm thinking that lower voltage would allow a smaller/cheaper X-former, or a switching power supply, as well as smaller caps, resistors..
Output in 0.5W to 5Watt range? driving a "small" speaker (6" to 8") + a line out to drive your bigger amp.
It doesn't seem important to me to defeat the speaker when using the line out; just set it on top of your big amp & let it play...

You could even build a "combo" amp all in one box, with tube driving 6" speaker and a big chip amp (LM3886..?) driving a 12"

also, seems to me that 110 volts demands respect, but 400V is looking for a way to kill you..

Another one choice
http://milas.spb.ru/~kmg/microfetpa_en.html
How it sounds (with transformer changed to different type to match with speaker impedance, 4x12 cabinet) at only 75mW of output power.
Cabinet is connected directly to output transformer winding, preamp is tube bogner ecstasy.
http://milas.spb.ru/~kmg/files/projects ... mp/13A.WAV

PS Possible Russian trafo replacements
http://eu.mouser.com/catalog/643/1110.pdf

KMG, that sound clip sounds pretty cool! nice little project!

So basically its like a mini power amp that can be easily overdriven to give the BIG overdriven power amp type of sound? the idea is still to put it thru a cabinet and mic it but you have option for an emulated line out too for going straight in for recording direct? whats the output bypass for?

Cool design! thanks for posting!

Hello KMG
NICE ONE!
-What is the Data(Prim+Sec) of the TOT60-Trafo???-
Thanks Thilo

So basically its like a mini power amp that can be easily overdriven to give the BIG overdriven power amp type of sound?
the idea is still to put it thru a cabinet and mic it but you have option for an emulated line out too for going straight in for recording direct?

Version on my website was designed specially for line recording. But now I want to make some changes for it.
1-st, change trafo for matching with cabinet (clip recorded using TOT57 & 8 Ohm cabinet). I plan to order xicon trafos & test them for sound.
2-nd, dummy load must be complex (not simple resistive), look at the frequency response (voltage at pa output) on resistive load & cabinet

So I plan to use something like that: When no cabinet jack inserted, this load is connected to micro pa output & voltage on it is passed to frequency correcting circuit to match cabinet/mic frequency curve.

whats the output bypass for?

Because this project was a part of preamp I added PA bypass switch for possibility to have "DRY" (without PA) preamp output to play into high power head/combo using loop return input.

-What is the Data(Prim+Sec) of the TOT60-Trafo???-

Russian transformers databook:
http://milas.spb.ru/~kmg/files/literature/Malogabaritnye_transformatory_i_drosseli.(1985).zip
TOT transformers from page 316
Partially translated:
http://milas.spb.ru/~kmg/files/literature/tot.pdf