Valvecaster woes part Duex.

[goldstache]

Working on understanding my valvecaster project.  It's operating at 12 volts with a 7812 regulator. Other than the regulator it is currently stock.
Wondering what gives with pin #6?  It ranges from 4-6 volts dependent on what 12AU7 tube I am using.  "Healthy and Suggested" readings are in the 8 volt range.  What gives?
Here are the pins:
1    3.12
2   -0.38
3    0
4    0
5    11.89
6    4
7    -0.28
8     0
9     5.94
I am a noob and could really use some knowledge.   
Also any ideas on how to lower the noise floor?  And to reduce farty bass.  I have tried cathode cap in parallel, and lowering cap to grid to .022uf
Thanks in advance.

[petemoore]

  Can't see the schematic.
   Pin 1 is plate, shouldn't this be close to the V+ supply voltage ?
   Pin 6 is also a plate [anode of the second triode].
  there is most likkely a miswire...
   Adressing the noise floor after the tube is biased is suggested.
  As far as bass mud, a triode like the 12a_7 @ such a small voltage potential may have troubles producing linear bass response.

[goldstache]

Thank you so much for your time.  I am unsure why the readings on the plates are so far a away from V+ value of 12 volts.  The resistors present are 220K plate 1, and 100K to plate 2. 

Here's the schematic I was using from BA.....


http://www.diystompboxes.com/smfforum/index.php?topic=63479.msg500470#msg500470

Could it just be bread board anomaly??

[PRR]

> ranges from 4-6 volts dependent on what 12AU7

Yes. A well-fed tube circuit's plate will vary +/-20%. This under-fed 12V scheme is even more likely to vary. 2V-3V would be wrong; 4V-6V seems acceptable to me.

You could try reducing R3 to 50K.

> why the readings on the plates are so far a away from V+ value of 12 volts.

That's the supply voltage. The tube and the plate resistor tug-of-war against each other. As a general thing, the plate should sit at "about half" of supply, 1/3rd to 2/3rd, or 4V to 8V in a 12V system. To get large gain on very small signals, you give the tube the short end of the rope, 1/4 to 1/2 or 3V in a 12V system; that's how the first tube runs when gain pot is full-short. If you watch while you dial some resistance into VR1, the plate voltage rises from 3V to 6V, 8V, or maybe more.

> lower the noise floor?

It should not have excess hiss, just a normal tube (which is comparable to a TL072 like we use everywhere). It IS a HIGH-gain circuit so any noise will be loud.

[goldstache]

Thanks so much!  I felt my brain getting bigger.  Oh wait!  That was just happiness that it is within characteristic.  Fun circuit with a simple soul!!!!!