Powering tubes in a car...

[Steves908]

I've decided on it. I want to integrate vacuum tubes into my car stereo. Sounds like a fun challenge. It'll probably be a line stage amp with 12AU7's or such. But, the real challenge here is getting a B+ voltage from 12Vdc. The heaters are taken care of with the car's 12V (of which I'll regulate). I want the B+ supply to be as simple as possible. A complicated and costly solution would be to use a 110Vac power inverter and a step up transformer, plus a rectifier.

But, what if I used an inexpensive, low wattage (<100W), 220Vac power inverter and rectified that directly for around 300Vdc? I understand the danger of using mains power without an isolation transformer, but would this case be different because with an automobile we know where the power is coming from (proper grounding etc.)? If this is a poor choice, what would be another alternative to avoid a power transformer. Any advice appreciated.

Here's a 220V inverter that looks suitable: DY-100 100W DC 12V to AC 220V USB Car Power Inverter (Silver) ERAA1S - $17.59 - Affordable Car Inverter

[madtecchy]

Hi Steves have you set a budget for this project.

Regards Ian

[Steves908]

It doesn't have a set budget, but I'm trying to keep the project as simple and affordable as possible. Not using a power transformer would help in both cases, so I'm just curious.

[yoaudio]

Just buy a car tube amp.

Milbert Amplifiers, Most Musical Amplifiers

[DigitalJunkie]

You could build a voltage doubler from the inverters output,thus eliminating the big heavy step-up transformer.

If you feel like some hackery,you could remove the H-bridge from the inverters output,and use just the HV DC output.
Or,tap off the secondary of the inverters HV transformer,and put a doubler there (use fast diodes)..I've done exactly that and had about 320V B+,and from a 300W rated inverter,plenty of current.

Check out this thread, 12 volt to 300 volt inverter question for tubes

[Steves908]

Hi DigitalJunkie, thanks for finding that thread. That's pretty much what I had in mind. Glad to know it'll work!

[n3n0]

Do you know Milbert Audio?
They have a fine amplifier, 100% valvulated.
But in car use, the problem of voltage is always present.

[Doz]

I've just completed a tube amp for my car. It uses a butchered "cheapo" car inverter, designed to give 230 V "Pseudo sine wave" at 50Hz. I've tapped the rectified HT off from the switched mode before the H-bridge, and filtered it, gives about +320V under load.
This feeds 4 6550 beam tetrodes, suspended on little rubber mounts (think CD player transport here), driven by 6N6P phase splitters and a 6N6P input tube. Really pleased with it. Getting round the problem of the cars electrically noisy environment involved the use of input transformers to isolate the grounds. 6N6P are Russian NOS, and I've had no microphony problems so far.
The bias supply is derived from a tiny mains transformer off the output from the H-bridge, rectified and filtered to give -50 volts. The design is loosely based on Triodedick's Mono Bill.... any why? ... because I can !

[speaker]

You could try something designed for lower B+ like 6DJ8's too. There are some single-ended 24VDC preamp designs out there already using that tube. That greatly lowers the bar for power supply design by using 12VDC to 24VDC converters off the shelf. For the filaments you series-string them. There are also some sub 30VDC complimentary power-supply preamp designs for the 6DJ8. In that case you could use an existing car amplifier and take your power right off its +/- rails.

Just a thought

[Doz]

This is a power amp, I can't see a 6DJ8 producing much in the way of output power. OK if you want to drive a pair of headphones I suppose, or just have a pre-amp