Tube Cricket Amp Layout

[texasfuzz]

This is the Tube Cricket that Dano made the schematic for while Beavis Audio was still cooking circuits.

The layout below is based on his schematic.  I built it a few nights ago to verify it and it works great.  I currently only have it pushing my 12" test cab, but it should get a 4x12 moving too - and its only approx 1/2 watt!  The tube is a 12AU7.

The layout file and some pics of my build are at www.texasfuzz.com if interested.

As far as biasing goes, basically adjust VR1 and VR2 down to around half of the voltage measured at bias point 3 (I used SIP sockets at the bias points to make it easier to position my meter while adjusting the trimmers).  The only other trick to this build is that the 386D is preferred over an LM386, I got mine at Small Bear.

Have a nice day!

[Frank_NH]

Very cool.  Thanks for sharing!

I have a bunch of NOS preamp tubes that I haven't done anything with.  This may be a good first tube project.

[texasfuzz]

You're welcome!

I like the one I built quite a bit.  

I think it's a very worthy project to make use of one of those spare 12AU7's you might have laying around.

[MOPO]

Hello,

Could anyone tell me which speaker would be the most appropriate for this circuit (size and impedance?).

Thank you

[Tesla]

Full frequency is a must, 4-5” speaker is fine and the wattAge really doesn’t matter that much in this case as it’s such a low power amplifier.  Really you’d be far better off buying of the 50w hifi amp modules like a bunch of us have done. These a lengthy topic about it and there of really epic quality.  Best part is you can build what ever preamp or eq you want for giving you more control over the eq.  Mine has my 5150lll PCB In the front end of it, with a 8ohm 8” full frequency speaker I have 50w. If you use 4ohm you’ll have more like 30w

The impedance on this one I believe is 8ohms as well

[MOPO]

thank you,
I have seen maybe the vison BG20 - 8 OHM which seems to be not too bad and for the tube 12AU7 RT005 or the EHX.

The goal is to make me a small nomadic amp.
and try me on the tubes :)

@ +

[MOPO]

Hello,
I have built and seem to work very well masi I can not adjust the bias like indicate, the best I can do is:

Item 3 = 10.59
point 2 = 5.30
point 3 = 6.40 (I can not go down lower the trimpot is at bottom)

Otherwise I have to add a spdt switch to the on / off of the amp.
in feed input I 've 11.79, that' s probably where the problem comes from?

Despite that the sound is very good, I tested it on a hp x4 8 ohms

If someone has a trick for setting the bias I'm a taker :)

thank you
@ +

[Travis]

Just at a glance the layout is missing the cathode bypass caps for both triodes so you’ll get more gain if you include those. The 386 has such limited headroom I imagine it probably sounds better without the cathode bypass caps though!

You could use a bigger value pot or series resistor to bring the voltage down. Although 5.3V is ridiculously close to half 10.59V

Personally I wouldn’t even bother changing it

[MOPO]

I will follow your advice and leave it like that, since the sound is very good, better than what I had imagined, it is especially the point 3 at 6.40 that worried me but I finished the setting in a box like that and this little amp is really cool.
I build a small hp to make a little nomad on vera if the sound is correct in this config too.
For the lamp I used a tube amp doctor.

Thank you
@ +

[Sold(i)er]

Hello all. This is my first post here. Thank you for a fantastic community and above all for you special human beings drawing the layouts. I have built around 80 effects on vero and perf so I’m not a complete newbie to this. I have built the Tube Cricket twice and both times ended up with a puzzle. Without the tube I get the 12V from the PSU as I should. When I insert the tube, the voltage on bias point 3 is only 4.33. This is my first project with a tube so I am not so familiar with the inner life of tubes. Can anyone help me or point me to the right direction?

Thanks!