• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

So any ideas for a car type amp?

This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
It had to happen.
I race karts and spend much of the day working on the kart between races. I know I could do this much simpler but I dont like shallow gradients in life.
I figure 5 watts or so should do the trick.
Firstly what valve(s) , I would love to use a pentode as the input stage( to avoid 2 stages as it where)
Secondly, I could use an inverter (pure sine wave) but I am thinking a dc to dc converter along the lines of Steve Bench's as I figure there will be less losses.
I may need to find some unobtanium but am looking as we speak.
Thanks for your time
Nick Mega
Hi Nick. I've been daydreaming about some of the same ideas as you.

I am currently building my own BIG high-power car amp based on LM3886 audio amps but one day I would like to build a well powered tube amp.

I realized early on the challenge was not really the amplifier but the SMPS (power supply). I built some that are +/-35V and have PCBs as well. Also built the Silicon Chip magazine tube preamps, that have a DC-DC 12V to +260V supply.

I am saying I know it can be done.

There are almost no examples on the web but I'm pretty sure modifying the transformer ratio in the SMPS to provide the +300V or whatever it is will do the trick.

What do you think? I don't have a real starting point for the amp design itself either...for high power I mean (maybe 50W +/-).

I don't know if you'll get good replies here as almost no one has ACTUALLY BUILT a high power car tube amp in DIY, just little 1W or whatever units.

Fun fact: Years ago there was an award winning BMW with a Milbert BaM-235ab tube amp (very expensive) I noticed was based on an old Milbert design. Racked up a load of awards and magazine articles.
I used to race carts and found that headphones made for helicopters are the best option. They are not very hi-fi-ish, but good enough to silence a motor sound and reproduce a music well. The main drawback, of course, is attention that a music takes from the cart driving. But a plus is, you may take a cheap inverter and get 170V from it that is enough to power a decent amp that drives headphones. You'll need a filament transformer only that may be an ordinary one made for 60 Hz frequency. However, I assume an American inverter, 120V AC/ 60 Hz.
However, the construction has to be very rugged, optimized for weather conditions, vibrations, and accelerations.
Hey Guys

Thanks to all for replying.
Marty is on the right track for my intended use. Many think I am odd anyway, but to race with music may well encourage the men in white suits to rescue me!
To be clear, I want to be able to listen to music whilst in the pits, between racing as it where or when I'm practising. If I am happy with the results of the tube escapades for my Trailer, I will then turn my attention to my car(s). I know this is doable but of course its new territory.
The trailer I have wil have a large boat type deep cycle gel battery so I need to limit power consumption to a realistic level. I figure keeping the design simple with as few tubes as possible will help.
Marty, at least your wish to build one for the car isnt limited by the need to run solely of the battery, so for 50W you would probably do alright with a 6550 type tube with accompanying input tubes and phase splitters.
The easy option would be to build a coventional amp and use an Inverter and hang the inefficiency.
You might be able to modify an "inverter". That's a device that takes 12V car battery power and converts it to what they call a "modified sine wave" 120V output. All that is is a square wave with dead time inserted at zero crossings, to produce 120V RMS though the peaks are about 150V, a little like the peaks of the real powerline. I think all they do to create that is to have a SMPS DC-DC converter to go from 12V to 150V DC, and then use switching FETs in a bridge circuit to create the modified sine wave output. You might be able to just grab the 160DC ahead of the FET bridge. This assumes that there's isolation between the 12V in and 160V out, or that the negative end of that 160VDC is strapped to either side of the 12V in. If the positive side of the 160VDC is strapped to the 12V, that's a bit ackward...
im looking at building some tube amps for my car to i see one company has already started doing them but with a price tag of £5 grand pluss i dont think i will be buying one besides that would be no fun
i have used inverters from 12 vdc to 240v ac before and they are useless much to much humm and a horribe ac frequency out
the other problem i can see is correct me if im wrong the use of a false ground for want of a better word at car ground =12vnegative i may have got that wrong
so to summerise i want to use an el34 type amp so the problems i have are bumping 12 v dc up to 350v ish and 150v ish
then once thats sorted things should be straight foward possibly
i would like to hear peoples views on how to go about this or if youve done it even better
many thanks

link for car valve amps http://www.genesiscaraudio.net/press/genesisp15.doc

althought these may just be valve buffered solid state amps on further inspection but they did it some how but how ??
on second thought i came across this
my thinking is this car audio speakers tend to be very efficient in my case i run diamond hex components 91db so with 1 watt i get 91 db or there abouts so with even a modest 3.5-4 watts you are looking aprox 100db quite reasonable im not into deafening myself
so heres the idea i found a ab circuit very simple only 2 13m7 s per ch which is bassed around a 24v supply much easier to come by than 300 odd volts from scratch
then i got to looking at the other amps on this site
http://www.dogstar.dantimax.dk/tubestuf/mnibl2-2.htm that came up it is only 1 watt but runns from a 12 volt supply boosting it to 35v dc for the grid bias could this form a basis for another higher power amp such as an el34?or it could be uprated to provide the 35v grid bias voltage for the 3.5 watt class a amp
bot amps have a built in pre amp which can be tweeked to become a line driver type circuit i think
any thoughts
Hi Jamie.

If you want to do that, you can certainly do it.

Basically you will need to duplicate what I'm doing currently for building a multi-channel (chip amp based) car amp:

1. switching power supplys, with higher output voltage
2. Your amplifier(s) module

The SMPS (switchmode power supply) will provide an isolated ground on it's output side; this will also, in the case of preamps, etc., allow eliminating ground loop noise. I've done it-it works! (Used that on my tube preamps in the car)

I'm not saying it's easy. But if you read the principles behind SMPS designs you will see it will take a much higher turns ratio when you build the transformer vs. what you would use for a typical car amp supply (say 300V vs. 28-35V)

I have found some simple high-power tube amp schematics on the web but confess I am waiting to finish my chip amp amplifier before starting down that road.

Take a peek at this:
Tube amp-813 based (high power)

Also, I found the schematic on which the Milbert car tube amp versions are based on somewhere on the web...but they're more complex schematics.

Get a working SMPS with proper voltage output and you're 'home free' almost.

That's how I got my tube preamps (+260v) working in the car. Same principle.


PS: I think you're right about most of the "tube" car amps...a lot were (or may still be) solid state transistor based with tube preamps, not 100% tube. My old Planet Audio HVTs were like that.
I did some crude tube car audio experiments a few years ago. I even went so far as to drop my 845SE into the trunk of a Mustang and run it on a 1KW inverter. I also tried a KT88 P-P amp and a 6L6CG P-P amp. All of the amps operated reasonably well on the inverter with some mild raspy hum in the LT88 amp.

I found two problems that are not mentioned here. All tubes exhibit some degree of microphony. Some are far worse than others. The microphonic effect of the tubes pick up the road noise, amplify it and feed it to your speakers. You need to test out the tubes that you intend to use before hand and select some quiet ones. DHT's don't cut it even though it is in the output stage. Large input tubes like the 6SL7 are worse than small ones like the 12AT7. Industrial versions with triple mica are even better (5751). Parts that are mounted by soldering the wires to the tube socket pins (common point to point wiring) will come loose. They must be suported by the component body or mounted on a PC board. The whole chassis should probably be mounted on some vibration reducing suspension. I am sure that the severity of these effects depend on the vehicle type, road conditions and driving style.

I think that it would be relatively simple to modify the circuitry from an inverter to generate the needed B+. Attention to the other details will require some further experiments.
Thanks for the info Mr. Tubelab! :spin:

It's awesome to have that real world info about car application of the tube amps. I've haven't gotten that far and had not taken that into account yet so I'll be sure to add dampening/anti-microphonic attempts to my "to-do" list.

Nice photos on your site!
Here is an amp from Jogis Röhrenbude:


  • el84-6w.jpg
    33.8 KB · Views: 205
An externally hosted image should be here but it was not working when we last tested it.

As I type this, my PP 6v6 Magnavox console amp is being powered by a 500W inverter connected to a Motorcycle battery. I cant detect any audible differences between the inverter and mains power. My fisher KX100 sounds fine as well. Heck, if I buy a deep cycle battery, I could still have the sweet sound of tubes during a power outage.

Are you using a better "true sine wave" DC-AC inverter or one of the average or 'el-cheapo' units? Also did you have any issues to speak of with the voltage under load from the inverter?

I think one of those might be quite useful for spending less time getting a tube amp running in the car for testing purposes.

Also it would be easy to modify it for working with the "remote" lead used for car stereos.

MartyM said:

Are you using a better "true sine wave" DC-AC inverter or one of the average or 'el-cheapo' units? Also did you have any issues to speak of with the voltage under load from the inverter?

I think one of those might be quite useful for spending less time getting a tube amp running in the car for testing purposes.

Also it would be easy to modify it for working with the "remote" lead used for car stereos.


It's just an el cheapo unit I bought at best buy last year to run an electric drill out in the woods for tapping maple trees to make maple syrup. Under load, even when connected to the fisher, it maintained 115VAC output according to my VTVM. I believe that even the basic ones have some kind of internal regulation.
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.