Instructables

9 volt battery to power 5 watt tube amp

i searched for so long for the internet to answer me and nothing
i want an inverter that will take a 9 volt battery and power a 5 watt tube amp.
the amp is handwired, there's no circuit board
and i want to believe its possible



andy707074 months ago

As people have said, it simply isn't possible with a standard 9V PP3 battery. It's just too small and not powerful enough. The power drain would be too high and PP3s are rated at about 500mAh so even if you could build something that'd do it, at 100% efficiency it'd be drained in a few minutes. More likely it'd just overheat and catch fire.

If, however, you are asking if you can use a 9VDC supply then that is entirely possible provided it has sufficient current, you just need a relatively high powered inverter. It's a bit hard to know what you mean as unfortunately '9V battery' has become synonymous with 'PP3/6LR61 battery' though I'm thinking you mean the former as there aren't many other types of 9V battery out there. It would be feasible to run it from a 12V SLA battery but don't expect it to last very long.

gadabout554 months ago

I won't bore you with the math. The simple facts are this. The energy required by even a 5W tube amp is far greater than what is available from a 9v battery. You could certainly build something that does what you want, but unfortunately it would only run for at most a few minutes before your battery was drained.

5W at 120V RMS at oh lets say 20% efficiency (which is probably generous for the massive heaters in a tube amp = 50W and then 80% efficiency for the inverter equals 60W input at 9V would be ~7A. Draining a 9V battery at 100% efficiency into a magic circuit that stores all that energy and unloads it at a constant 9V would mean a battery rated at 0.58Ahr divided by 7A would give 300 seconds of operation before it was completely drained. In reality if such a complicated circuit could be built it would likely include joule thieves and super high-Q capacitors for preloading the burst of energy required to drive the inverter. It would probably be max 50-60% efficient including capacitor leakage, the DC-DC step-up converter and switching regulator losses, both are needed as the battery voltage drops. Maybe it would run for 150 seconds or less and would take ~1 hour to charge without overheating/exploding the 9V battery (max current at ~0.5A maybe). I think it could be done, just wouldn't be very practical or effective. Now if it were a 9V solar cell charging all day for a 1-hour concert or something that may be different...

I think you're full of pride. Anything is possible.

No chance. What drives the HT ? What drives the heater current ?
Magic :-)