'Rascal Mk1' Low Voltage Tube Amp build thread! (with PCB files & images)

[sebsongs]

I've recorded some sound examples of the amp now. Check it out!

http://soundcloud.com/sebsongs/guitar-amp-sound-examples

/Sebastian

[slacker]

Wow that sounds great, the higher gain settings are much better than on mine. I wonder if that's as a result of using a proper output transformer, I might have to get hold of one and try it.

[sebsongs]

I'm using the fender 22921 transformer as you know. It's not intended for amplifiers but it does sound great with my Jensen C8R.
Wouldn't use it with anything else than a 4 ohms speaker for this project though. It's pretty high ratio so an 8 ohms speaker would be too quiet, I think.
Great price on that OT on musikding.de. Something like 12 Euros.

/Sebastian

[petemoore]

  Very nice sounding amp.
 Amazing for 36v B+, and with common 12a_7 tubes !
 Seems like perfect candidate for the scaried beginner tube amp cobbler.
 ..or someone who'se not yet been able to build a small enough tube amp !
 Kudos with the transistor buffer-driver implementation, what a fine ''concept position'' [we haven't seen much of this...yet] for a transistor, way to follow through with it !  
 
 

[Morocotopo]

Sebastian, very nice looks! Not a man of many controls in your amps, eh?



One question: how did you get the grill cloth so straight? I never seem to be able to get it nice and straight...

[sebsongs]

 Very nice sounding amp.
 Amazing for 36v B+, and with common 12a_7 tubes !
 Seems like perfect candidate for the scaried beginner tube amp cobbler.
 ..or someone who'se not yet been able to build a small enough tube amp !
 Kudos with the transistor buffer-driver implementation, what a fine ''concept position'' [we haven't seen much of this...yet] for a transistor, way to follow through with it !  
 
 

Thanks!

Actually I'm powering it with just 32V. But yeah, I'm amazed about how it turned out.
Bear in mind though, it does not play at rehearsal volumes. It does not compete with the loudness of acoustic drums.
But as a home amplifier for practicing and recording, it's ideal - especially when you live in an apartment like me.
And it is of course possible to up the B+ voltage and get more out of the tubes. That is always an option.

Anyway, I'm having a lot of fun with this one. My LM350 is getting extremely hot though, so I need a larger heat sink to get it to acceptable temperatures.
It actually started making a sort of sinus tone noise today when I played it at maximum volume for a long time. The heat sink was really burning so I guess the LM350 started self oscillating or something. Anyone have an idea about what happened?

/Sebastian

[sebsongs]

Sebastian, very nice looks! Not a man of many controls in your amps, eh?



One question: how did you get the grill cloth so straight? I never seem to be able to get it nice and straight...

Haha, I like simplicity and the panel really got simple. The circuit has a tone control also, but I put it in as a trimpot, and I've adjusted it to it's maximum setting anyway.
I'm going to build an Electro Harmonix Knockout Attack EQ pedal and have that as EQ soon. I'll post a new thread about that later. I'm actually building 5 pedals now. =)

The grill cloth was mounted with a staple gun. Luckily the cloth has very distinct lines and was easy to line up with the edge of my front baffle.
The front baffle is detachable so I have mounted the cloth before stickin' it in the amp. But it was just a case taking my time and lining everything up as exact as possible and checking twice before stapling it. I started with one side, and got that as straight as possible, and was then able to strech the cloth real tight and stapling it on the other side. If you look real close it is not totally straight though. But it looks good enough for a first ever guitar amp build, I think.

Hope that helped.

/Sebastian

[fair.child]

Hey Sebastian,

where can I find the schematic and entire documentation for this project
I really want to build this !!!!'


Cheers