#124 Questions

[Bombacaototal]

My amp is running 460V / 461V at the 6L6 plates. I have it bias at 30.7mA (similar to #102 layout biasing). Should I go hotter at around 34mA?

[Bombacaototal]

My amp is running 460V / 461V at the 6L6 plates. I have it bias at 30.7mA (similar to #102 layout biasing). Should I go hotter at around 34mA?

I am thinking of going up to 34mA or Maybe 36mA. 60% would be almost 40mA. I am using a couple TAD 6L6WGC-STR Blackplate (30W).

What would you guys advise?

EDIT: I tried 34mA, 35mA and 36mA and settled around 36.5mA

[erwin_ve]

My amp is running 460V / 461V at the 6L6 plates. I have it bias at 30.7mA (similar to #102 layout biasing). Should I go hotter at around 34mA?

I am thinking of going up to 34mA or Maybe 36mA. 60% would be almost 40mA. I am using a couple TAD 6L6WGC-STR Blackplate (30W).

What would you guys advise?

EDIT: I tried 34mA, 35mA and 36mA and settled around 36.5mA

Do you use 1 Ohm resistor or voltage across OT or current shunt method. For the first one you easily can add 3-4mA extra because of the screen-grid current that is added with the plate current. 30,7mA is with the 1 Ohm resistors 33,7-34,7mA(mV reading). So a 33,7mA reading is actually more like 30,7mA. 36-37mA is still very safe and on the cold side, nothing to worry about.
What did you notice in sound going up a few mA?

Erwin

[Bombacaototal]

Thanks for the reply Erwin, I use the 1 ohm resistor and the measurements are done from the bias testing points. As I went up on the mA the amp became fatter, and I felt the low and high end were then more balanced. At 30mA it felt a bit more sterile and the high end bothered me more, but I also dod some tube swapping between the 30mA and the latest test from 33mA until 36mA

Good to know that I am still within safe range. I was tempted to go higher but decided to stopping there. Maybe tomorrow I will go up some more

[pompeiisneaks]

Thanks for the reply Erwin, I use the 1 ohm resistor and the measurements are done from the bias testing points. As I went up on the mA the amp became fatter, and I felt the low and higher end were then more balanced. At 30mA it felt a bit more sterile and the high end bothered me more, but I also dod some tube swapping between the 30mA and the latest test from 33mA until 36mA

That's definitely biasing a bit cool no? I see at 460V for 6L6GC you want around 45mA. (from the weber bias calculator) or are they really old 6L6? If so then 28.9 is the 70% mark so depends on which. If you bias cold, I do believe you tend to lose some of the deeper end etc. So yes pushing it more towards 70% will give you a better tone, imo. I've played with cooler bias on a few amps and felt it seemed too 'hifi' for me, and I prefer the tone at hotter bias.

~Phil

[Bombacaototal]

Thanks for the reply Erwin, I use the 1 ohm resistor and the measurements are done from the bias testing points. As I went up on the mA the amp became fatter, and I felt the low and higher end were then more balanced. At 30mA it felt a bit more sterile and the high end bothered me more, but I also dod some tube swapping between the 30mA and the latest test from 33mA until 36mA

That's definitely biasing a bit cool no? I see at 460V for 6L6GC you want around 45mA. (from the weber bias calculator) or are they really old 6L6? If so then 28.9 is the 70% mark so depends on which. If you bias cold, I do believe you tend to lose some of the deeper end etc. So yes pushing it more towards 70% will give you a better tone, imo. I've played with cooler bias on a few amps and felt it seemed too 'hifi' for me, and I prefer the tone at hotter bias.

~Phil

Hi Phil, thanks for the reply. No these are new production tube. My 6V6 (Groove Tubes Premium) is running 418V on the power tube PIN3 and I have it aset at 17mA - 60% range I think (and I absolutely love the sound of that amp).

I always thought Dumble went for the 60% range. I thought 60% at 460V for 6L6GC (30W) would be around 39mA/40mA. Maybe I can try pushing it more then..

[erwin_ve]

Thanks for the reply Erwin, I use the 1 ohm resistor and the measurements are done from the bias testing points. As I went up on the mA the amp became fatter, and I felt the low and higher end were then more balanced. At 30mA it felt a bit more sterile and the high end bothered me more, but I also dod some tube swapping between the 30mA and the latest test from 33mA until 36mA

That's definitely biasing a bit cool no? I see at 460V for 6L6GC you want around 45mA. (from the weber bias calculator) or are they really old 6L6? If so then 28.9 is the 70% mark so depends on which. If you bias cold, I do believe you tend to lose some of the deeper end etc. So yes pushing it more towards 70% will give you a better tone, imo. I've played with cooler bias on a few amps and felt it seemed too 'hifi' for me, and I prefer the tone at hotter bias.

~Phil

Phil, Although 45mA isnt the danger zone Dumble biased his amps on the cold side. The change in sound Raphael decribes is exactly what I focus on when biasing. There is a certain point around 50% where the amp gets balanced, smooth.

[pompeiisneaks]

Thanks for the reply Erwin, I use the 1 ohm resistor and the measurements are done from the bias testing points. As I went up on the mA the amp became fatter, and I felt the low and higher end were then more balanced. At 30mA it felt a bit more sterile and the high end bothered me more, but I also dod some tube swapping between the 30mA and the latest test from 33mA until 36mA

That's definitely biasing a bit cool no? I see at 460V for 6L6GC you want around 45mA. (from the weber bias calculator) or are they really old 6L6? If so then 28.9 is the 70% mark so depends on which. If you bias cold, I do believe you tend to lose some of the deeper end etc. So yes pushing it more towards 70% will give you a better tone, imo. I've played with cooler bias on a few amps and felt it seemed too 'hifi' for me, and I prefer the tone at hotter bias.

~Phil

Phil, Although 45mA isnt the danger zone Dumble biased his amps on the cold side. The change in sound Raphael decribes is exactly what I focus on when biasing. There is a certain point around 50% where the amp gets balanced, smooth.

Oh cool, I learned something new today

I didn't realize that part. Odd I've always disliked the amp too cool. Guess it goes to show how much everyone has different views on tone

~Phil

[erwin_ve]

That's definitely biasing a bit cool no? I see at 460V for 6L6GC you want around 45mA. (from the weber bias calculator) or are they really old 6L6? If so then 28.9 is the 70% mark so depends on which. If you bias cold, I do believe you tend to lose some of the deeper end etc. So yes pushing it more towards 70% will give you a better tone, imo. I've played with cooler bias on a few amps and felt it seemed too 'hifi' for me, and I prefer the tone at hotter bias.

~Phil

Phil, Although 45mA isnt the danger zone Dumble biased his amps on the cold side. The change in sound Raphael decribes is exactly what I focus on when biasing. There is a certain point around 50% where the amp gets balanced, smooth.

Oh cool, I learned something new today

I didn't realize that part. Odd I've always disliked the amp too cool. Guess it goes to show how much everyone has different views on tone

~Phil

It is indeed a matter of taste. I definitily like my Hrm amp around 60%. Most of the Non hrm just above 50%.

[martin manning]

It is indeed a matter of taste. I definitily like my Hrm amp around 60%. Most of the Non hrm just above 50%.

When quoting % dissipation it's best to include the basis on which the figure is calculated, i.e. the assumed Pa max, and whether the percentage is based on Ik or Ia. ;^)

[Charlie Wilson]

Most real Dumbles I have been inside were biased a bit warm. Over 40mA with Fender Twin plate voltage.
CW

[Bombacaototal]

Most real Dumbles I have been inside were biased a bit warm. Over 40mA with Fender Twin plate voltage.
CW

Thanks for the feedback CW. I will play around with mine today between the current (36.5mA) all the way up to 40+mA and see where I like it best. I shall report back.

[erwin_ve]

Most real Dumbles I have been inside were biased a bit warm. Over 40mA with Fender Twin plate voltage.
CW

Cw, interesting! are you refering to 440v plate voltage with fender twin?

Erwin

[erwin_ve]

It is indeed a matter of taste. I definitily like my Hrm amp around 60%. Most of the Non hrm just above 50%.

When quoting % dissipation it's best to include the basis on which the figure is calculated, i.e. the assumed Pa max, and whether the percentage is based on Ik or Ia. ;^)

Yes, pa max 30w 6L6GC, percentage on Ia. Being very precise:what's your preference when biasing?

Erwin

[martin manning]

Hi Erwin, I've been running my low-plate ODS biased at ~48 mA Ik, at 425V Va, so that would be 68% of 30W, actual Pa about 63%.