Bias of preamp tubes

[Robert]

I have recently been interested in the bias on the preamp tubes. At Dogears suggestion, I hung a 150K resistor off my power supply dropping resistors at the B5 node to simulate the load from the FET circuit. This dropped my voltages after a little resistor adjusting on V1 to 165 and V2 to 195. I really like the result eventhough V1 is on the low side. I will try to get it closer to 200. It really improved the tone,singing quality of the sustain and response to pick attack of the OD where it was previously at 129. A bit of high treble was taken away from the clean. I would like to hear any comments or thoughts regarding the aspects of bias for pre amp tubes. I have seen very little about this at the usual amp forums and have long thought it would make an interesting thread here.

[dogears]

What is your dropping string values?? You should not have 30v difference between V1 and V2 unless you are running the 97 schematic with maybe 12k between them. Try the Hybrid A values. I have about 202 on V1 and 210 on V2. You can use a 180k instead of the 150k to get a little more voltage as well.

I have recently been interested in the bias on the preamp tubes. At Dogears suggestion, I hung a 150K resistor off my power supply dropping resistors at the B5 node to simulate the load from the FET circuit. This dropped my voltages after a little resistor adjusting on V1 to 165 and V2 to 195. I really like the result eventhough V1 is on the low side. I will try to get it closer to 200. It really improved the tone,singing quality of the sustain and response to pick attack of the OD where it was previously at 129. A bit of high treble was taken away from the clean. I would like to hear any comments or thoughts regarding the aspects of bias for pre amp tubes. I have seen very little about this at the usual amp forums and have long thought it would make an interesting thread here.

[Robert]

The great oracle from the east said:

You should not have 30v difference between V1 and V2 unless you are running the 97 schematic with maybe 12k between them.

You are right -- pretty damn amazing!!!! I need a better supply of 2 - 3 watt resistors to tweak it closer but it is interesting how it sounds even with such a voltage difference. I hoped someone would comment on the effects of differing bias on the tubes.

[dogears]

I believe 1 watters should be just fine....

Typically the lower plate V will give less headroom and a more organic breakup.

The great oracle from the east said:

You should not have 30v difference between V1 and V2 unless you are running the 97 schematic with maybe 12k between them.

You are right -- pretty damn amazing!!!! I need a better supply of 2 - 3 watt resistors to tweak it closer but it is interesting how it sounds even with such a voltage difference. I hoped someone would comment on the effects of differing bias on the tubes.

[MarkB]

Just to be clear, the bias voltage is measured from cathode to grid. The bias voltage sets the idle current through the tube. What you are discussing is plate supply voltage. Important, no doubt, just not bias.

For a discussion of bias, see this:

http://aikenamps.com/WhatIsBiasing.htm


We now return you to the subject of this thread....

[dogears]

I knew that... I knew what Robert was really asking..... Afterall, I am the Oracle in the East!

Just to be clear, the bias voltage is measured from cathode to grid. The bias voltage sets the idle current through the tube. What you are discussing is plate supply voltage. Important, no doubt, just not bias.

For a discussion of bias, see this:

http://aikenamps.com/WhatIsBiasing.htm


We now return you to the subject of this thread....

[Robert]

MarkB thanks for the clarification between plate voltage and bias voltage. Aiken's articles are great reading, I just forget I read them sometimes.
Dogears said,

I knew what Robert was really asking.....

Now if everyone else could just read my mind.....

[MarkB]

I knew that... I knew what Robert was really asking..... Afterall, I am the Oracle in the East!

And I knew that you knew.