Tube Cricket Debug Help

[Kultur Vultur]

Hey, I bought a Tube Cricket kit from OLCircuits a few weeks ago and I can't quite figure out what's wrong with it. It just hums loudly and if I strum really hard I can faintly hear my guitar in the midst of the humming. The only component that isn't orignal is the voltage regulator because it didn't work out of the box. I replaced it with one from the parts bin and now it outputs 12V like it should.

Both Bias points are at +9V

Here are some voltages:

Tube:
Pin 1: 9.5V
Pin 2: 0.0V
Pin 3: 0.0V
Pin 4: 11.3V
Pin 5: 0.0V
Pin 6: 9.0V
Pin 7: 0.0V
Pin 8: 0.7V
Pin 9: 5.7V


NJM386:
Pin 1: 1.3V
Pin 2: 0.0V
Pin 3: 0.0V
Pin 4: 0.0V
Pin 5: 5.3V
Pin 6: 10.7V
Pin 7: 5.2V
Pin 8: 1.3V

As far as reference material goes, I have this: http://www.olcircuits.com/documents2008/olc_tubecricket_buildguide.pdf

Any help would be really appreciated, thanks.

[Pushtone]

You may want to compare your voltage readings to mine.
http://www.diystompboxes.com/smfforum/index.php?topic=68510.0

Mine seems to be working but with some hum.
Best guess in that thread is that the hum is caused by the LM chip i used instead of the recommended JR chip amp.

I need to do a big parts order to get the right chip and try it.

Anyway our chip voltages look the same but our tube voltages are different.
Have a look and see what you think. I think my tube is working correctly because I can audio prob it with clean sound right up to the chip amp input.

Wish I could be more help. I'm in the same boat with you.

Dave

[Kultur Vultur]

Our voltages are indeed different at the tube plates. Your plates are around 6V while mine are around 9V. The OLC build guides perscribes 9V for the plates but the schematic linked to in your thread perscribes 6V. This is odd, perhaps I will try biasing at 6V.

Your second cathode (pin 8 ) is also about 5V higher than mine...

Seeing Dano's post in your thread, I double-checked the power supply for the JRC386 and it is connected to Vcc instead of Vin on the OLC board. Seems good.


Any thoughts?

[Pushtone]

I think we need to ask OLC about the difference in plate voltages.

I'm in a holding pattern until I take the time to order the right chip.

Then I'll update my original thread.

Dave S.

[Kultur Vultur]

So I replaced all the pots and it works okay I suppose. The "gain" knob doesn't do anything and the tone knob works more like the "cut" control on some amps in that as its turned up, it removes treble. However, the thing does make noise and it, in fact, sounds pretty decent. Not ideal performance, but it least I can play guitar through it, right?

Some hum, as well. There's about 5VDC at the output that I can't figure out how to get rid of...

[kurtlives]

5VDC at the output is a lot. Is the amp crackling as well?

Could be a missing or bad coupling cap.

[Pushtone]

Some hum, as well. There's about 5VDC at the output that I can't figure out how to get rid of...

Ah... Did you read the last lines in my thread.

"I also metered the speaker out jack
Speaker Output: 4.1VDC
Thats the hum right there!!
This would sound so good if were not for the constant hum. "

Me

We's gots da sames hum. Chip???

[Kultur Vultur]

The amp does not crackle at all. It only hums. If I turn the volume way up I get bizarre behavior from it, though. It's a strange thumping that increases in frequency as the volume gets closer to max. I have no idea what that means, though I do note that if I bias the tube plates to 9VDC instead of 6VDC, the volume knob needs to be higher for the thumping thing to happen.

Pushtone, I'm using a JRC386.

This is odd...