Tube amp for my car

[wa2ise]

Originally Posted by ctc17

I was thinking of that but with a 12AX7 type tube.

There's the 6112 twin triode submini tube, somewhat similar to a 12AX7. With a reasonable mu around 70 IIRC. It's a 6.3V heater tube, but use a pair and build an SRPP circuit, and the heaters in series to run them off the 12V car power. With wire leads you could just solder into the circuit, so no tube getting loose issues, and it's designed for mobile work.

I had not though of opening the inverter and removing the chopper fets. Brilliant!

thanks.

All you need to do is ad the 2nd and 4th order harmonics to give it the tube sound.

That's the ticket.

[lnx64]

As how much power is required, I have a 140 amp alternator, and my engine idles roughly at 900rpm. It idles like that because it's a 350 chevy small block with a 400 crank in it, making it a 383, along with it's cam profile.

So even at idle, im sure I can get some power in the electrical system that should be useful for something.

But using these simpler designs are interesting too.

[N2IXK]

Originally Posted by wa2ise

And you may be able to take apart an inverter to get at the high voltage DC before it's chopped into square wave AC, to get the B+ for the tubes.

Are you thinking of a switchmode AC-DC power supply? Every 12V-120VAC inverter I have seen does the primary side switching at 12V, and the AC voltage is just stepped up using a transformer. No high voltage DC available.

[wa2ise]

Originally Posted by N2IXK

Are you thinking of a switchmode AC-DC power supply?

More modern, and smaller ones, look to be switchmode DC to DC converters running somewhere around 30KHz or higher, with subsequent choppers to make it look like 60Hz AC squarewave. Assuming that the DC-DC conversion has no DC path between its primary and secondary, or if the negative end of the secondary side is tied to the input 12VDC, you can use it for B+ ahead of the 60Hz chopper ckts. You may need additional filtering to get rid of switching crud off this B+.

If you have an inverter that runs at 60Hz 12V to a 60Hz transformer, and the secondary is isolated, just feed it into a bridge rectifier and filter caps to get the B+.

[lnx64]

Ok so I tried a bit of what was recommended, especially feeding the tubes that can, off of 12v directly.

I can get sound, and it's feeding the speakers sound that can get fairly loud. Only issue is, while it's seemingly not causing the volt meter on my car to go low at all, and voltages are ok and normal so far, but my check engine light oddly comes on, on super bassy music (like 90's alternative rock), and it's always the same trouble code from the cars computer, right O2 sensor read error.. Very weird, but when I disconnect the amp, the code goes away. It doesn't always do this with the amp attached though.

Anyway, here's an audio sample. I won't be able to keep this video up, it's being scrutinized for the music contents.

http://www.youtube.com/watch?v=_w-h263ur10

EDIT: And I did notice, at 1:28, when the songs bass starts playing, I have noticed some distortion in the bass guitar sounds. It's as if the tubes are possibly suffering from enough current, but are getting the voltage though.

For the other stuff that needs an inverter, I chose an inverter that produces the best sine wave, that I could find.

[Blast]

I did just this very thing in my '68 Chevelle in the late 70's with a Trio W-45 stereo integrated amp and a Tripp-Lite PV-150 150w power inverter. Don't remember what kind of under dash tape/radio thing I was using.

Originally Posted by ctc17

I can just hear the buzzing from the crappy stepped signwave out of the inverter.

And, that's exactly what I heard, as well. So, out it went.

[mstaton]

Probably not wise to run the filaments directly from the cars power due to the fact that it's at least 13.8 volts and higher when cold. Filaments wont be too happy. A regulated PS would be in order. B+ is 375V for the 7591's plus 200V+ and 160V for the others. The 12ax7's are already run in series in that receiver, However the rest are not. The current draw for that receiver is 3A max.. Removing the FM tuner and phono preamp tubes will raise the B+ voltages and is not advised without modification. Maybe just sell it on eBay. You'll get more than $200 for it easily and buy something better.

[wa2ise]

Originally Posted by mstaton

Probably not wise to run the filaments directly from the cars power due to the fact that it's at least 13.8 volts and higher when cold. Filaments wont be too happy. .

A series power resistor, or even the resistance of the supply wiring may be all you need to get it to 12.6V.

Something else to be very mindful of: When mounting the amp in the trunk or anywhere else, be very careful where you drill holes for screws or anything else. You really don't want to drill a hole into the gas tank, catalytic converter, exaust, drivetrain and such. And be sure that where you do place a nut and screw or pointy end of a sheet metal screw won't get hit by something as the car bounces along on a bumpy road. And be sure you can still get the spare tire and jack out if you ever need to. Or some access port the mechanic may need to get into (fuel pump switch and such).

If your proof of concept test works out, you may want to take the iron out of the amp, and custom build a chassis to create a new amp to fit. And use rugged tubes.

Drop by AudioKarma, our sister forum site. one is for car audio http://www.audiokarma.org/forums/forumdisplay.php?f=149
and tube audio http://www.audiokarma.org/forums/forumdisplay.php?f=14