Biasing Problem

[SISKO]

Lately ive been having some problems with one of my tubes amps. The sound come and go with no secuential order and i found that the bias level was shifting. so i measured the voltage at the bias point with no tubes in and i read 0v all over the bias circuit.
Next thing i did was to disconect the bias circuit read the voltage at the end of the power resistor and found 0v.

So basicaly my problem its this.

(400v ac)--- (100k 2w)-|<|--- (to bias circuit)

On the anode of the diode i have no voltage BUT if i touch the node between the 400v and the resistor and then measure again the anode i have 50v but starts to decrement to 0v, as a capacitor discharge.

I measured the resistance and it gives me 100k i tried other Rs and its the smae thing. I tried to put a 10M resistor from the node to gnd, but it didnot help.
My guess is that, the resistor with such a high voltage its changin its value to something bigger. Ill put a smaller resistor.
Am i missing something here?

[GibsonGM]

Can you post a schematic of the whole biasing network?  Your problem may show up at the resistor, but could be a bad cap or something elsewhere.   If the resistor is good, leave it....it's 100K for a reason!  Could also be a problem with the diode, but there isn't enough information to make a good guess for you...is this home-brewed, or from a known working schematic? Etc.

[SISKO]

Its a Marshall 2550 clon. I didnt post the schematic becouse with the little diagram i made i tough it was enoguh.
Anyway, here it is:
http://www.drtube.com/schematics/marshall/2550amp.gif
http://www.drtube.com/schematics/marshall/2550psu.gif

You may want to kill me, but this mornig when i was at school i had
9vcc--470R--multimeter

and it read 6v, so i guess maybe the MM its with battery low. This affternoon im going to try a fresh one and tell you my results.

[SISKO]

It was the low battery causing the estranged reading.  Now on, ill always replace the battery when the indicator its marking
Next step, try to look for another problem in the amp