Depending on the tube lineup and if the output is isolated you can likely strategically ground the heaters in a way that they don't make any appreciable noise. For example, 2x 60V heaters on an isolated 120V inverter can be ground between the tubes and it'll be pretty quiet. If you have to use those same two tubes but can only ground one side of the 120V output the tube that isn't at ground will likely hum because cheap inverters normally use square wave inversion which will induce much more via the heater than a sine wave does.
Now, you can just rectify the 120V output and run the heaters on DC in which case it wouldn't matter. A really cheap inverter likely uses square wave at ~120V so you might just need a diode and a cap which makes DC easy.
Now, you can just rectify the 120V output and run the heaters on DC in which case it wouldn't matter. A really cheap inverter likely uses square wave at ~120V so you might just need a diode and a cap which makes DC easy.
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4 X 26E6 and 3 X 12AY7 would need 118 volts at 300 mA. The output of most cheap inverters is a square wave with some dead time such that the average power is close to a 120 volt sine wave. Direct use should heat the tubes correctly.
The peaks however are usually in the 140 to 150 volt range so that things that rectify the wall outlet will also work. This means that a rectifier on its output will likely give 140+ VDC. This will be too much voltage for the tube heaters. Only an experiment will tell what you get.
The inverter internally generates a DC voltage, then 4 mosfets chop it up into a pseudo sine wave. It may be easiest to tap into the internal DC for B+ and heater voltage.
I did simply plug a big tube amp into an older 700 watt inverter and it worked with only minimal buzz. The amp however didn't live long in the trunk of a Mustang on the pot hole infested south Florida roads.
The peaks however are usually in the 140 to 150 volt range so that things that rectify the wall outlet will also work. This means that a rectifier on its output will likely give 140+ VDC. This will be too much voltage for the tube heaters. Only an experiment will tell what you get.
The inverter internally generates a DC voltage, then 4 mosfets chop it up into a pseudo sine wave. It may be easiest to tap into the internal DC for B+ and heater voltage.
I did simply plug a big tube amp into an older 700 watt inverter and it worked with only minimal buzz. The amp however didn't live long in the trunk of a Mustang on the pot hole infested south Florida roads.
Is the DC tap point generally easy to locate?
I shouldn't point out the wrong-thinking here. 6.3V tubes were MADE FOR use in automobiles. (That's why the ".3".) They heat *directly* off the car battery. I understand you can still get 6V heat tubes.
I was toying with the idea of building a tube based car amp years ago. I found that most tubes, even output tubes like the 6V6 and 6L6GC were microphonic enough to make audible sounds when operated in the trunk of a Mustang driven over the pathetic roads we had on my morning commute in Florida. I even tried running my 845SE amp on a 700 watt power inverter, but a pothole killed one of the DHT filaments. Fortunately it was a Chinese tube and not a vintage GE.
I tested a bunch of different tubes and discovered the 26E6WG. These guys were designed for SE audio output duty in airplanes. The guts look like a 6V6 cut in half with each half mounted next to each other. They are all but immune to vibration induced microphonic noise. At the time I had designed a 12 to 28 volt boost converter for a high powered mobile radio, so I just retuned one for 26 volts. I obtained B+ by stealing the HV out of a European 12 volt to 240 volt AC inverter.
Before I ever finished the amp, federal and state grant money made my project unimportant. The entire city got repaved, and I came to the realization that the traffic noise made having a serious stereo in a convertible rather useless.....I just fixed the factory Ford Mach 460 stereo.
In an European unit you would connect your output across the only 300 or 350 volt cap in the thing. I imagine you would look for a 160 or 200 volt cap in a US unit. The 240 volt versions are available on Amazon now as are 12 volt to 26 volt boost converters.
I tested a bunch of different tubes and discovered the 26E6WG. These guys were designed for SE audio output duty in airplanes. The guts look like a 6V6 cut in half with each half mounted next to each other. They are all but immune to vibration induced microphonic noise. At the time I had designed a 12 to 28 volt boost converter for a high powered mobile radio, so I just retuned one for 26 volts. I obtained B+ by stealing the HV out of a European 12 volt to 240 volt AC inverter.
Before I ever finished the amp, federal and state grant money made my project unimportant. The entire city got repaved, and I came to the realization that the traffic noise made having a serious stereo in a convertible rather useless.....I just fixed the factory Ford Mach 460 stereo.
In an European unit you would connect your output across the only 300 or 350 volt cap in the thing. I imagine you would look for a 160 or 200 volt cap in a US unit. The 240 volt versions are available on Amazon now as are 12 volt to 26 volt boost converters.
Stick the words "boost converter" into Amazon's search engine and see what turns up. There are plenty of "DC to DC 3.0-30 V to 5-35 V Output Voltage Adjustable Step-up Circuit Board" to choose from. Realize that the capabilities are probably exaggerated a bit, but many of these do work, and cost less than the individual parts would cost us to make one. The output is ground referenced which is OK, and these are probably cleaner than trying to use series wired tubes on 120 volts.
There are also several versions capable of making B+ voltage some are regulated and some are not. I have experimented with some of them, but not seriously enough to make a complete amp.
These things seem to come and go, and none of the simple unregulated versions that I bought almost 2 years ago are still listed. Neither are the Philips 240 volt inverters that I cannibalized for my 12 volt to 280 volt power supply which still works.
There are also several versions capable of making B+ voltage some are regulated and some are not. I have experimented with some of them, but not seriously enough to make a complete amp.
These things seem to come and go, and none of the simple unregulated versions that I bought almost 2 years ago are still listed. Neither are the Philips 240 volt inverters that I cannibalized for my 12 volt to 280 volt power supply which still works.
In my experience, unless the inverter is square wave, it'll work fine. I had a UPS that used stepped sine (looks like a wedding cake) that I had an old tube amp plugged into. With pure sine from the outlet, there was audible 120Hz hum from the outputs, but when powered from the stepped sine inverter, it was silent. Apparently it's easier to filter for the built in RC filter.
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