Channel voltage mismatch

[misok]

Hi,

i've recently finished s simple preamp based on 6N6P tube (6x4 LCLC rectifier). i really like the sound but a mystery (to me) appeared.

in breadboard version, both plate voltages were desired 160V (470 Ohm cathode resistors). in final wooden chassis i got reading from one channel 160v, but other only 75 or so. just before plate resistors they are both 280, which is right. one side of double triode glows a bit less as well. i checked cath resistance - both 470 ohm. i changed the tube - same result. i also tried to insert the tube cca 5x to get rid off some possible oxidation in the socket. hearing-wise there is just a subtle difference but i'd like to solve this.

thanks for any opinions in advance.

all the best,

misok

[DF96]

Cathode voltages? Missing grid resistor?

[misok]

Originally Posted by DF96

Cathode voltages? Missing grid resistor?

cathode voltage is correct 6v on the 'ok' channel, on the wrong one is around 10.

there are no grid resistors, i use cowon player as a source and it worked fine (= equally and with good voltages) breadborarded. so my idea is to tune it as it is (hum wise) and then add a stepper attenuator that i have.

[DF96]

So what is grounding the grids for bias purposes? You can't use a step attenuator unless you can guarantee that it is make-before-break and will not fail.

[TubeHead Johnny]

Do you have a schematic handy?

[misok]

Originally Posted by DF96

So what is grounding the grids for bias purposes? You can't use a step attenuator unless you can guarantee that it is make-before-break and will not fail.

thanks ! i just soldered 100k resistors across both channels and the voltages are both right. i still don't get it since before there were no grid resistors and voltakes on plate/cath matched, but now they do again and i can sleep well. one side still glows a bit less but it has to be a matter of a certain tube. it sounds good now.

i used this (well known) schematic http://diyparadise.com/web/images/stories/yeo5687.gif but with a 6N6P double triode. it sounds great even before fine-tuning values of cathode components.

[DF96]

Your breadboard version must have provided a conducting path for the grids, either deliberately (resistor) or accidentally (leakage).