10-30 mW Guitar Power Amp with Genuine Power Tube Distortion

[hardi_ami]

Hello

Not my schematic, but I just came over this :
http://home3.netcarrier.com/~lxh2/lowpsch.html

I think it could be easily adapted as a pedal use, but since I don't know anything about tubes I can't help

If anyone is interested to mod it ...

Michael

[aron]

I've seen this before but never tried it.

hmmm.... :?

[EdJ]

I think i have the transformers needed.No more T.V. for me tonight

[hardi_ami]

EdJ, I'm ordering the output transformer needed for that project from a german site (tube-town.de) but do you know any other way to get output transformers at a better price (because Hammonds are expensive...) in Europe ?

Thanks !!
Michael

[EdJ]

Well you could try AE Europe in Schagen,The Netherlands.I bought a PT there and they were very cheap.To be honest i don`t know their OT`s but the place looked good and the people were very knowlegeble.
They have a website but i don`t remember the URL.Try google.
Greetings,Ed

[Joep]

AE is a known and highly regarded in hifi-land.

They have a website:
http://www.ae-europe.nl/

Bye,

Joep

[hardi_ami]

Thanks but hmmm I don't speak that language
I've ordered from tube-town.de a hammond output trans. 125E and 2 EL84, as soon as I get them I'm ready to build !!

EdJ, have you started building it ? I've got a question concerning the heating filaments of the tube : can I use 6V instead of 6.3V ? If not, do you know how to get 6.3v from a 12v supply ? (I mean, a better solution than divider bridge)

Thanks

Michael

[Peter Snowberg]

You can always wire the filaments in series and just use 12V. That will work just fine.

Have fun!
-Peter

[hardi_ami]

Ok thanks I'm just going to buy a 2*12V of something like 15VA transformer then, use 12V AC unregulated to heat the filaments, and use some LM7812 and LM7912 with a couple of capacitors after a diode bridge to get +12V and -12V regulated relative to ground. Am I right ?
Since the heaters of 2 EL84 take up to 1.5A (on 6V), and the opamps draw almost nothing ... (that can't be dealt by the LM regulators)

I wouldn't dare heating the filaments with the regulated 12V... I think those LM can only handle 1A each.
Any comment before I kill me ?
Thanks

Michael

[Peter Snowberg]

If you get too much hum, you can always give the tubes DC heater voltage using a bridge rectifier, a big capacitor, and a couple of heavy duty diodes to reduce the voltage to about 12 to 12.5 VDC. You can also use a small value resistor instead of the diodes.

The LM317 is good for 1.5A (with a big heat sink), but you can use a 7812 with a big PNP pass trasistor to get 12 volts at as many amps as you want.



Either of these solutions will coexist nicely with your +12/-12 supply.

Instead of a 2*12v transformer, you might want to think of using a single secondary 12 volt transformer with a center tap. This way you can ground the center tap, you can use the secondary 12V for the heaters, and you can use voltage doublers coming from each side of the secondary to generate the +12 and -12. If you use a good op-amp, you don't actually need the 7812/7912 regulators. The doublers should give you roughly 14-16 volts depending on the diodes and capacitors you use. You can always use 15 volt zeners to clamp the output of the voltage doublers. I would use some sort of regulation there for sure.

-Peter