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heater voltage for 12ax7 - is 11.7 volts enough?
Old 14th April 2004
  #1
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fatty's Avatar
 
๐ŸŽง 15 years
heater voltage for 12ax7 - is 11.7 volts enough?

still testing \ tweaking my valve mic pre. i've got 260 volts for the ht, which is exactly what the design calls for, but i'm only getting 11.7 volts on the heaters from my power supply. is this gonna be ok, or do i really need to figure out where i'm loosing 0.3 volts and fix it? it seems to work fine at 11.7, but i dunno, am i gonna shorten the life of the valve or anything??
Old 14th April 2004
  #2
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gyraf's Avatar
 
๐ŸŽง 15 years
11.7V is all you need.

It's well within the 12.6V +/-10% that most 12V-tubes are specified for. Running low-power (preamp) tubes a bit underheated prolongs their working life.

Power output tubes is a different story - much discussion about those. Specially the directly-heated power triodes.

Jakob E.
Old 14th April 2004
  #3
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fatty's Avatar
 
๐ŸŽง 15 years
thanks jakob.
Old 15th April 2004
  #4
Here for the gear
 
๐ŸŽง 15 years
You can run them at 6.3vac, too if they are run in paralell. Series or DC operation requires 12v on the heaters.
Old 7th June 2009 | Show parent
  #5
GCA
Here for the gear
 
๐ŸŽง 10 years
11.7 is OK, but...

Quote:
Originally Posted by Cinemafixer โžก๏ธ
You can run them at 6.3vac, too if they are run in paralell. Series or DC operation requires 12v on the heaters.
6.3 DC is fine in parallel as well. They'll draw 300mA each in 6.3 whether DC or AC. I built a power supply to test this out; I've got a switch for unregulated 6.3VAC and regulated 6.3VDC from the same transformer winding. The numbers really do add up like the datasheets say, haha.

The biggest difference is that at 12.6 in series each heater will draw 150mA while at 6.3 in parallel they'll draw 300. Either way is fine, though for the original question I'd try to get closer to the 12.6V. 11.7 *WILL* work, but keep in mind that at a slightly lower temperature on the heater you will /change the characteristic curve of the tube/. Be careful dropping the available voltage 900mV like this as it can have a very real effect on the sound since it's so close to the outside of the 1.26V tolerance.

(uhm.. hi everybody, I'm a n00b to the gearslutz forums but I've read many many posts when searching the web for stuff.)
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