I'm try to learn how load line work's. So, I understand that the grid voltage can't be more positive than 0v. But when I try to draw the load line with a 6021, I can't get bias correctly I only get positive bias. What I'm doing wrong?
Plate voltage of 60v.
Thanks.
Plate voltage of 60v.
Thanks.
Plate voltage is way too low... Try 150V B+ with 100V on the plate and 8k load resistor and see how it looks...
Here's a great resource, too:
https://wtfamps.com/load-line-calculations/
And a loadline calculator that makes this kind of thing really easy:
https://www.vtadiy.com/loadline-calculators/loadline-calculator/
Here's a great resource, too:
https://wtfamps.com/load-line-calculations/
And a loadline calculator that makes this kind of thing really easy:
https://www.vtadiy.com/loadline-calculators/loadline-calculator/
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But the max plate dissipation is 1.1W. So, 1,1/150 = 0,0073A or 7,3mA. 20mA ( 8k plate resistor ) with 150V it's very much. No?
And how engineers do, with low voltage supplies? I see a lot of preamps and pedals that work's with this tube at very low voltages.
And how engineers do, with low voltage supplies? I see a lot of preamps and pedals that work's with this tube at very low voltages.
The B+ is 150V. The plate voltage is 100V. The 8k resistor drops 50V. That means 6.25mA of current across the tube. 100V * 0.00625A = 0.625W of plate dissipation. This doesn't accound for the ~1V across the cathode resistor but it's close enough.
They either use a DC-DC boost converter to get higher voltage, or they starve it for voltage/current since it's an effects pedal in that case and not for HI-FI.
They either use a DC-DC boost converter to get higher voltage, or they starve it for voltage/current since it's an effects pedal in that case and not for HI-FI.
There are many who want to use tubes at very low voltages, tubes that were meant for more moderate or higher voltages.
If you choose to design at such low plate voltages, versus how the tube was designed to operate, then . . .
The results are extremely variable, from one tube to the next. Same manufacturer, different vintage, different manufacturer, etc.
Perhaps the only "practical" use of the 6021 at very low plate voltages, is for a guitar fuzz box.
That would be a great place for a post on the Instruments & Amplifiers threads of the diyAudio forum.
By the way, operating the 6021 at that quiescent condition, there will be grid current, which will distort the signal that comes directly from the guitar to the 6021 grid. That adds to the fuzz that is also coming from the non-linear portion of the plate curves.
Just my opinions.
If you choose to design at such low plate voltages, versus how the tube was designed to operate, then . . .
The results are extremely variable, from one tube to the next. Same manufacturer, different vintage, different manufacturer, etc.
Perhaps the only "practical" use of the 6021 at very low plate voltages, is for a guitar fuzz box.
That would be a great place for a post on the Instruments & Amplifiers threads of the diyAudio forum.
By the way, operating the 6021 at that quiescent condition, there will be grid current, which will distort the signal that comes directly from the guitar to the 6021 grid. That adds to the fuzz that is also coming from the non-linear portion of the plate curves.
Just my opinions.
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I'm thinking building an hybrid guitar amp. Tube pre and solid state power amp. So, my voltage rail is 60. Maybe I go for a korg nutube?
what do you think?
what do you think?
Try using a really good plate choke. The DCR of the choke can be less than the resistance of a plate load resistor.
With a lower DCV drop from 60V B+, you might get the tube to work better.
Caution:
A plate choke will pick up any magnetic fields around it. Power transformer, power supply choke, output transformer.
I think some Lundahl products have mu-metal shields on them; that would reduce the sensitivity to magnetic fields.
The spacing between the plate choke and the B+ choke, poert, and output transformers is important.
And the angular orientation of the plate choke versus the other magnetic fields above is important.
Instead of a plate choke, you might consider using a CCS that has less voltage drop than a plate load resistor.
Many 60V power supplies can be modified to include a voltage doubler (120V).
You have a lot of engineering decisions and calculations ahead to do.
Good luck, and happy designing!
With a lower DCV drop from 60V B+, you might get the tube to work better.
Caution:
A plate choke will pick up any magnetic fields around it. Power transformer, power supply choke, output transformer.
I think some Lundahl products have mu-metal shields on them; that would reduce the sensitivity to magnetic fields.
The spacing between the plate choke and the B+ choke, poert, and output transformers is important.
And the angular orientation of the plate choke versus the other magnetic fields above is important.
Instead of a plate choke, you might consider using a CCS that has less voltage drop than a plate load resistor.
Many 60V power supplies can be modified to include a voltage doubler (120V).
You have a lot of engineering decisions and calculations ahead to do.
Good luck, and happy designing!
There are tubes that can work with lower B+, also tubes designed for battery supplies, and even car radios at 12v.
With your hybrid amp, what were you wanting the tube to do?
Just read your earlier post. So tube pre - with tone controls?
With your hybrid amp, what were you wanting the tube to do?
Just read your earlier post. So tube pre - with tone controls?
Yes,
Guitar tube pre with tone stack. The korg nutube have 80v max plate. But I don't know if it's special or different in terms of biasing.
Plate Voltage: 60
Anode Resistor: 60/0,01=6k
Grid: -0,75V
Grid Resistor: 0,75/0,005=150R
Dissipation: 35V*0,005=0,175W
More or less... ?
Do you mean Cathode resistor? Isn't the current the same as the anode, so I = V/R, 0.01 = 0.75/R, R = 75R?
EDIT: A cheap source is to use PCC84, the 300mA heater version. Did a quick check and Siemens NOS are €5 from one source.
EDIT: A cheap source is to use PCC84, the 300mA heater version. Did a quick check and Siemens NOS are €5 from one source.
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