Need help for Tube Cricket

[soapamp]

I do the assemble tube cricket job for my friend.  I have the problem on the voltage bias 1 & 2.  My DMM read the voltage at VCC point 11.78. I try to bias 1&2 by turn the trimmer to 3/4 the voltage is just 11.50. It could not go down to 9v as mention on the instruction.  I use DC 12v power supply.  How to debug this problem

[Transmogrifox]

Do you have a schematic for this?   If so, post it or post a link to it.  I'm not sure where to find the tube cricket layout or schematic.

It sounds like either a solder joint is bad or there is a solder bridge where it shouldn't be.  If you built it from a kit on a PCB, just go back through the circuit part for part and make sure it's continuous through parts where it should be, and doesn't have continuity where it shouldn't.

[Scruffie]

A little off topic, but how did it sound? I haven't found a single sample and I'd like to know it was worth committing too before I build it, instead of just a standard cricket or ruby.

[dano12]

Hi dude! what schematic did you use for this? I think there were several floating around....

what values did you use for trimmers?

[soapamp]

Trimmer is 100k

The schematic   http://www.diystompboxes.com/smfforum/index.php?topic=66623.0

[dano12]

If I recall there were a few times I had trouble biasing, depending on the tube used. Bumping the trimmer pots up to 250k or 500k solved the problem.

[soapamp]

I used 12au7.

[Transmogrifox]

I know this is pointing at the obvious...but, you do have 12V connected to the heaters, right?  Just taking a stab in the dark.

If all else is properly connected, then you may consider reducing  R7 and R11 to 1k.  I don't know how close your 12V supply is to 12V.

What do you measure on the power supply?

Assuming it's right on 12.0V, then there's pretty much zero current through your tubes.  Accounting for a diode drop, I would deduce your heaters aren't connected (pins 4 and 5).  My second guess is there is a bad solder connection at the plate and/or the cathode.

The fact that both tubes have the same problem indicates the heater isn't connected.   Double check your heater pins.
http://en.wikipedia.org/wiki/ECC82  just to cross-check your pinout.

A quick way to find out is measure voltage between ground and pin 9.  If pin 9 is at about 6 volts then the heater is ok.