Bias not stopping to zero

B&WTube wrote:3 out of 4 of my bias pots have the same setting to reach .450 and the other is much lower on the pot dial to achieve.450. Upon playing with it this bias, I noticed that even  if I turn it all of the way down- it still reads .160

Also- this is the bias that controls the socket where I recently blew a power tube (already replaced).

Furthermore there is considerably more hum coming out of my right speaker vs my left.

Thanks, in advance, for advice I still have a lot to learn.

B&WTube wrote:Thanks, Bob! I went ahead and ordered those. It is amazing that I can purchase and get them shipped to my house for $2.59 total.

Do you know of any good tutorial that can walk me through the basics of what NOT to do/touch when testing internal voltages? I have never done anything inside of the amp with the power ON. I've heard there are things that if messed with have enough power to kill, and my kids still need me around for a few more years.

Dale Stevens wrote:B&W, hold on; Be sure you read the sticky here on SAFETY.

Bob, why not measure the bias res from the top without opening the amp??
       Just go from pin 8 on each power tube to ground?  Dale

B&WTube wrote:Could it be something to do with pin6 of V7, where it connects to the VTA board or the other wires off the VTA?  My triode wires are correct there is a place where the insulated wire touches a solder on the neighboring pin.

tubes4hifi wrote:going all the way back to post #1
1 - with power off, check each 10 ohm resistor on each output tube to ground, all should be within 9.5 - 10.5 ohms, if not, replace
2 - try swapping tubes around to see if the bias problem follows the tube or stays at that socket.   If it follows the tube, the tube is bad.
3 - with ALL tubes out of the amp, with each bias pot at center position, you should measure between 35-40vdc from each output tube socket pin 6 to ground.
     If ONE of them measures different, maybe that bias pot needs to be replaced.   They are 3386P type, and must be 50K ohms.
4 - with the power off, measure from the top of R29, top of R30, top of R31, and top of R32 to ground.
    With the bias pots set at center position, you should get a reading of 30.5K (from 30K to 31K)from each of those points.  
     (You'll need to wait about ten seconds for the reading to settle due to C17 in the circuit)   If one is way different, you've got a bad bias pot.

tubes4hifi wrote:going all the way back to post #1
1 - with power off, check each 10 ohm resistor on each output tube to ground, all should be within 9.5 - 10.5 ohms, if not, replace
2 - try swapping tubes around to see if the bias problem follows the tube or stays at that socket.   If it follows the tube, the tube is bad.
3 - with ALL tubes out of the amp, with each bias pot at center position, you should measure between 35-40vdc from each output tube socket pin 6 to ground.
     If ONE of them measures different, maybe that bias pot needs to be replaced.   They are 3386P type, and must be 50K ohms.
4 - with the power off, measure from the top of R29, top of R30, top of R31, and top of R32 to ground.
    With the bias pots set at center position, you should get a reading of 30.5K (from 30K to 31K)from each of those points.  
     (You'll need to wait about ten seconds for the reading to settle due to C17 in the circuit)   If one is way different, you've got a bad bias pot.