I am working on a preamp for a friend and was thinking about this idea:
I have a spare 6.3V winding available on the power transformer.
The main rectification is a bridge.
Can I connect a 6L6 as a diode in series after the main filter cap?
Would the screen be connected to the anode and the grid connected to the cathode?
I have a nice coke bottle 6L6 and it would provide a bit of slow turn on.
Do you see any issues here?
Low current.
Years ago I used triodes as diodes without and issue.
Or would a damper diode be a better choice. Unfortunately I don't have any atm, and want to stick to what I have. I suppose I can use my last 5Y3 for it need be but would rather not (would have to use dropping resistor to bring the heater down to 5VAC)
I have a spare 6.3V winding available on the power transformer.
The main rectification is a bridge.
Can I connect a 6L6 as a diode in series after the main filter cap?
Would the screen be connected to the anode and the grid connected to the cathode?
I have a nice coke bottle 6L6 and it would provide a bit of slow turn on.
Do you see any issues here?
Low current.
Years ago I used triodes as diodes without and issue.
Or would a damper diode be a better choice. Unfortunately I don't have any atm, and want to stick to what I have. I suppose I can use my last 5Y3 for it need be but would rather not (would have to use dropping resistor to bring the heater down to 5VAC)
You can do it, but why? In any case try a true diode, like a 6AX4 that are cheap, doesn't need extra trafo secondary and has less drop.
Osvaldo: why? I have the 6L6 and the spare 6.3v winding, not concerned about drop as I will be dropping a lot of volts anyway. If I had a 6AX4 or 6X5 I would use them
rayma: yes it is a separate spare 6.3v winding
rayma: yes it is a separate spare 6.3v winding
Go ahead and try it. It will drop some volts, but may not provide much of a slow turn-on
unless you switch its filament separately.
unless you switch its filament separately.
No, for 2 reasons
1) 6l6 cathode to filament is *peak* 200V DC and that is a "maximum rating", not design center value, compare to humble 6X4 which stands -450V peak or 350Vdc at the capacitor it´s charging.
2) 6.3 Vac winding itself must stand those voltages so I guess a "safe" insulation capability should be between 500 to 750V or so.
You could make it a slow turn-on by connecting the grid via an R-C to slowly bring it up to cathode potential.
Jan
No problem if you connect the filament to the cathode, if the 6.3V floats (as is the case here) and can stand the voltage.
Jan
What are the preamp tube types that need a slow turn on B+?
Are they super expensive?
Are they hard to obtain?
Are they being operated at or near the maximum tube ratings?
Are they guaranteed not to fail, even if a slow start B+ is used.
They might fail, even if you use a slow start.
Purchase some spares, before they become Un-Obtanium.
How fail-proof is the 6L6 circuit going to be?
Just my opinions.
Are they super expensive?
Are they hard to obtain?
Are they being operated at or near the maximum tube ratings?
Are they guaranteed not to fail, even if a slow start B+ is used.
They might fail, even if you use a slow start.
Purchase some spares, before they become Un-Obtanium.
How fail-proof is the 6L6 circuit going to be?
Just my opinions.
They are some slightly expensive 6DJ8's. The reason for this is more for looks - coke bottle 6L6 will look good on top of the chassis with the 4 6DJ8's. My friend loves the look of tubes. The slightly delayed B+ is just a small added benefit. How fail proof is the 6L6 diode going to be? I would say it is going to be pretty reliable.
imho, the cathodes of the 6l6 leaves too much to be desired, if you must, then a tv scanning tube will be much better, g1 to cathode, g2 to plate....
If you need a diode use a diode they cost about 40 cents
What does a 6l6 cost? $40 by the time it's at your door. Awful expensive diodes.
What does a 6l6 cost? $40 by the time it's at your door. Awful expensive diodes.
Wondering if the grid-cathode space charge can sustain the peak inverse voltage during turn on without arcing. Understand that you are using the tube in an abnormal way.
would using a 100k resistor from grid to cathode offer any help?
also, this 6L6 is a tube I have had sitting around for 20 yrs with no other use for it.
I would sell it and buy a box of these: 6CQ4 / 6DE4 Octal High Voltage Half Wave Rectifier Tube
Where in Ontario are you? I have a bunch of vacuum diodes I'll never use including a few dampers like this.
Where in Ontario are you? I have a bunch of vacuum diodes I'll never use including a few dampers like this.