I see the maximum filament voltage for the 12AT7 is 6.3 and the 12AU7 is 6.6
and as it goes my virtual center tapped ps is at 6.9
Should I leave it, or should I try to knock .5v or so off ?
If I wanted to work on a small reduction I was thinking there are two ways,
The virtual center tap config looks to be the standard 100 ohm resistor off each leg to ground.
At the sacrifice of more current through that 6.3 coil I could reduce the 100 ohm resistors a little
or
may be add a resistor in series with the heaters...
My gut kick is to add something in series...
Thoughts?
EDIT:
12AU7EH shows 6.6 (Electro-Harmonix)
Correcting my post now, after euro21 caught my error
and as it goes my virtual center tapped ps is at 6.9
Should I leave it, or should I try to knock .5v or so off ?
If I wanted to work on a small reduction I was thinking there are two ways,
The virtual center tap config looks to be the standard 100 ohm resistor off each leg to ground.
At the sacrifice of more current through that 6.3 coil I could reduce the 100 ohm resistors a little
or
may be add a resistor in series with the heaters...
My gut kick is to add something in series...
Thoughts?
EDIT:
12AU7EH shows 6.6 (Electro-Harmonix)
Correcting my post now, after euro21 caught my error
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Is the 6.9 volts read as loaded, (connected) or unloaded?
-----------------------------------------------------------------------------------------------Rick...
-----------------------------------------------------------------------------------------------Rick...
Where are you read 6.6V limit for 12AU7? In chinese or russian datasheet?
Genalex shows this value, but ALL genuine 12xx tube has 12.6/6.3V filament.
Genalex shows this value, but ALL genuine 12xx tube has 12.6/6.3V filament.
euro21 good call! The data sheet I pulled up was for a 12AU7EH The file name was simply Electro-Harmonix-12AU7.pdf..
6.3 it is!
Am I wasting my time worrying about the .6 above the 6.3 ?
6.3 it is!
Am I wasting my time worrying about the .6 above the 6.3 ?
Those tubes are BOTH 12 volt filaments, how do you determine that they run on 6 volts???
12 - AX7..... 12 - AT7
There ARE 6 volt versions of those tubes. = 6AT7, 6AU7
A 6 volt version of a 12AX7 is the 6EU7
As for actual running voltages, I wouldn't fuss or obsess over a fraction of a volt like some others seem to do - because tubes all have a tolerence built into them at the factory.
If the filament current is within its margin (300mA +/- 10%) the 0.6V above 6.3V isn't catastrophic.
If it bothers you, use dropping resistor (0.6V/0.3A= 2R).
If it bothers you, use dropping resistor (0.6V/0.3A= 2R).
If in parallel 6.3v
The 6.9 feeds 4 tubes, and all in parallel, i figure the amperage to be .3x8 or 2.4 amps total on that heater winding circuit.. that gave me a .25 ohm resistor. Because i want to do both sides (virtual center tap) i just ordered (2) 4 watt 0.125 ohm resistors.. probably won't make much of a difference, but what the heck its worth the few bucks for trying 😎
The 10% was something i was unaware of, thanks to both of you fine folks for making me aware.
The 6.9 feeds 4 tubes, and all in parallel, i figure the amperage to be .3x8 or 2.4 amps total on that heater winding circuit.. that gave me a .25 ohm resistor. Because i want to do both sides (virtual center tap) i just ordered (2) 4 watt 0.125 ohm resistors.. probably won't make much of a difference, but what the heck its worth the few bucks for trying 😎
Chris,
The tube has essentially a center tap, in parral the voltage was 6.3, i assumed that the .3 was for one side of the tube. Will have to measure!
The tube has essentially a center tap, in parral the voltage was 6.3, i assumed that the .3 was for one side of the tube. Will have to measure!
Look at post #10.
The tube specs are right there.
I'll spell it out... the 12 volt filament is center-tapped, and draws 150ma that way.
Now......
Paralleling that, and using the common connection of the center tap, will make it..... a SIX volt filament, drawing TWICE the current, or 300mA.
It's basic, elementary, electronics. = Ohms Law.
The tube specs are right there.
I'll spell it out... the 12 volt filament is center-tapped, and draws 150ma that way.
Now......
Paralleling that, and using the common connection of the center tap, will make it..... a SIX volt filament, drawing TWICE the current, or 300mA.
It's basic, elementary, electronics. = Ohms Law.
Not sure why you couldn't or didn't follow my logic, but ill spell it out for you. These tubes have 2 grids, 2 plates in each glass envelope. 12 volts in series would be both of the heaters wired in series, double the resistance and half the amperage, again simple ohms law..
My thought was if half a tube is at 6.3v, pulling .3 amps and we did this 8 times...
Again, i said I assumed, and would Have to measure...
Why does this thought process bother you so much??
Most folks here have been super friendly, i may have miss read your response but it hardly sounded anything but condensending.. if it was, please do yourself and me a favor, take a deep breath remember whats truly important in life and move on. Id prefer not to deal with this or you.. im here to learn, ask questions and enjoy my time..
If i did totally misread Your intentions, please forgive me
My thought was if half a tube is at 6.3v, pulling .3 amps and we did this 8 times...
Again, i said I assumed, and would Have to measure...
Why does this thought process bother you so much??
Most folks here have been super friendly, i may have miss read your response but it hardly sounded anything but condensending.. if it was, please do yourself and me a favor, take a deep breath remember whats truly important in life and move on. Id prefer not to deal with this or you.. im here to learn, ask questions and enjoy my time..
If i did totally misread Your intentions, please forgive me
A small series resistor is of value here, not only to reduce the filament voltage but also to reduce the
turn-on current peak.
Nominal heater current for 12AT7 and 12AU7 is 150mA each (6.3V) heater, so 150mA in series or 300mA in parallel. 8 triodes, 4 bottles need 8 times 150mA equals 1.2A.
All good fortune,
Chris
All good fortune,
Chris
First, a pair of antiparallel diodes will be needed. Second, of course they will dissipate the same heat as a resistor dropping the same voltage.
Best regards!
For AC voltages this is true ... usually i feed mine with DC. And the heat issue is also correct but they do the job...
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Chris,
Thats was my hang up, i didnt see or couldn't tell if the data sheet was talking about 1 side of the bottle or both, you have cleared this up, thank you for helping this beginner yet again!
The circuit is ac, and i though about the diodes, as mentioned i would need 2 in parallel.. what dissuaded me was the virtual center tap with both legs tied to the 100 ohm resistors to ground. I felt like whatever i did on one leg should be done on the other. 4 diodes or 2 resistors in total.
I have heard that in some situations and probably in other applications a diode could actually create noise... not knowing all i need to know, my intuition led me to believe a very low value resistor would be better. I also thought about the cutoffs in diodes, that the signal would not be as clean. Again untested and my thoughts are possibly based on ignorance.. i need more time behind the scope with components.
Unfortunately for me, time is the most difficult to find component!
That said, thanks to all who took the time, much appreciated!
Thats was my hang up, i didnt see or couldn't tell if the data sheet was talking about 1 side of the bottle or both, you have cleared this up, thank you for helping this beginner yet again!
The circuit is ac, and i though about the diodes, as mentioned i would need 2 in parallel.. what dissuaded me was the virtual center tap with both legs tied to the 100 ohm resistors to ground. I felt like whatever i did on one leg should be done on the other. 4 diodes or 2 resistors in total.
I have heard that in some situations and probably in other applications a diode could actually create noise... not knowing all i need to know, my intuition led me to believe a very low value resistor would be better. I also thought about the cutoffs in diodes, that the signal would not be as clean. Again untested and my thoughts are possibly based on ignorance.. i need more time behind the scope with components.
Unfortunately for me, time is the most difficult to find component!
That said, thanks to all who took the time, much appreciated!