12AX7 info help ....

[rx5]

1> what is the maximum heater voltage??

2> since almost all diagrams I see on them, they are wired in series...why not in parrallell.??

3> cant I power each heater with 12VDC??

4> what is the maximum PLATE voltage??

5> does parrallel wiring the 2 heaters (w/12VDC) make the tube life    shorter?? because it generates more heat...

6> does the death of the heater siginify the death also of the TUBE??

7> How do you know if a tube is DEAD?? with the heaters still glowing...


thanks for any info.... :oops:  

[Peter Snowberg]

1> what is the maximum heater voltage??

12.6 volts is the max you should ever use. Higher voltage = shorter life. A little higher = a lot less life.

2> since almost all diagrams I see on them, they are wired in series...why not in parrallell.??

In most amps with 6 volt power tubes, they are usually wired in the 6 volt configuration. For preamp only designs, 12 volt wiring reduces the amperage by 1/2. If the heaters are DC powered, you can use smaller diodes. Some devices also run the tube plates are 12 or 24 volts so it's just convenience.

3> cant I power each heater with 12VDC??

NO! You can power them both in series with 12.6 volts, but each heater is only 6.3 volts MAX.

4> what is the maximum PLATE voltage??

This depends on the specific tube. 300 volts is a good top rating. I have run them quite a bit higher, but it's not a good idea. (420 volts is the max I have used for an experiement)

5> does parrallel wiring the 2 heaters (w/12VDC) make the tube life    shorter?? because it generates more heat...

Think of putting 240 volts into a 120 volt lightbulb.... expect it die right away. You will ruin the cathode before the fillament quits.

6> does the death of the heater siginify the death also of the TUBE??

Yes.

7> How do you know if a tube is DEAD?? with the heaters still glowing...

Measure the voltages on the grid, cathode and plate. If you have high voltage on the plate, ground on the grid and a few volts on the cathode, you should see any signal on the grid reproduced on the plate at a much higher level (about 100 times for 12AX7). If the signal goes in but nothing comes out, well.... it's dead. If you have high voltage on the plate and the grid is at ground but you don't have any voltage on the cathode, the tube is dead.

Please observe the maximum ratings. They are there for a reason.

Take care,
-Peter

[rx5]

wow.... :twisted:  :wink:  :twisted:

thanks for the info man..... that'd really answer my Q's......  :lol:  




-Ralph :roll:  :wink:  :roll: