Heater power supply question

[pwnuts]

So, I'm almost ready to start my new project, a portable guitar amp. It's going to use a TA2020 chip as a power amp, and the Matsumin 12AU7 preamp circuit. My question is this: I have a 12v 4Ah lead-acid battery to power this project, and I read up that the 12AU7 needs 6.3v for the heater filaments. As it probably isn't a good idea to put almost double the heater voltage though it, would it be more sensible to use a 9v battery (as used in the schematic) or alter the voltage (xener diode, potential divider etc.)?

Thanks!

[defaced]

The "12" at the front of the 12A_7 designation means it has 12v heater. The thing about these tubes is that bthey have a center tapped heater to allow use with 12.6 or 6.3 v heaters. Check the datasheet for pinout. Im pretty sure its pins 4 and 5 for the ends of the heaters and pin 9 for the center tap.

[petemoore]

  Check some tube data, IIRC it's a 10% +/- recommendation to voltage variance from recommended heater voltage selections. If spare tubes aren't a problem, that 10% can be 'experimentally stretched'', running LV plates and 'saggy' filament voltage isn't recommended, overvolting filament tends to or shortens tube life.
   The charge state of the battery varies battery voltage too, I don't know whether to suggest a regulator for filament supply because of power consumption/heatsinking and only pretty sure there's a regulator which will keep 1? filament happy and supply sufficient current.

[amptramp]

12.6 volt heaters were used in car radios for quite some time and 6.3 volt heaters were used back in the days of 6-volt car batteries.  Heaters are really not all that critical and many tubes operate better below their rated heater voltage.  Car generator / alternator / battery systems were never all that stable as far as voltage was concerned but the radios survived.

[PRR]

12AU7 has _two_ 6V heaters which may be wired series (12V) or parallel (6V).

12AU7 takes 12.6V across pins 4-5 just fine (ignore pin 9).

> a 12v 4Ah lead-acid battery

A fresh lead-acid battery is THE design voltage for "12V" heaters: 12.6V. Car-battery.

Roaring down the road at 65, the generator could turn 14V; hundreds of miles like this is covered in the design.

Sitting in the driveway with the engine off and the radio going, the 12.6V will sag to 12V and 11V. This too is covered in the design: the power stage won't play as loud, weak-radio reception may decline a bit, but really no big change even when the car battery is too flat to re-start the motor. In your application, the TA2020 will be sounding weak while the 12AU7 are still plenty hot to do their job.