Bias of preamp tubes
Moderators: pompeiisneaks, Colossal
Bias of preamp tubes
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.
Re: Bias of preamp tubes
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.
Robert wrote: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.
Re: Bias of preamp tubes
The great oracle from the east said:
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.You should not have 30v difference between V1 and V2 unless you are running the 97 schematic with maybe 12k between them.
Re: Bias of preamp tubes
I believe 1 watters should be just fine....
Typically the lower plate V will give less headroom and a more organic breakup.
Typically the lower plate V will give less headroom and a more organic breakup.
Robert wrote:The great oracle from the east said: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.You should not have 30v difference between V1 and V2 unless you are running the 97 schematic with maybe 12k between them.
Re: Bias of preamp tubes
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....
For a discussion of bias, see this:
http://aikenamps.com/WhatIsBiasing.htm
We now return you to the subject of this thread....
Re: Bias of preamp tubes
I knew that... I knew what Robert was really asking..... Afterall, I am the Oracle in the East!
MarkB wrote: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....
Re: Bias of preamp tubes
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,
Dogears said,
Now if everyone else could just read my mind.....I knew what Robert was really asking.....
Re: Bias of preamp tubes
dogears wrote:I knew that... I knew what Robert was really asking..... Afterall, I am the Oracle in the East!
And I knew that you knew.