• 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.

Car Tube Amp?

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I'm curious if anyone on the forum has firsthand experience with 12V tubes or a design for a mobile tube amp?

I've been pondering this idea ever since finishing my Simple SE and being addicted to its sweet sound. What makes it particularly convenient is all the wiring is already present in the car to make this much easier, since it has a premium factory system with JBL speakers AND is bi-amped. I believe that the amp is rated at 15W RMS, and the subwoofer amp 85W RMS. Unfortunately, I do not have data on SPL / efficiency of the speakers.

So I have power, signal, and speaker wires in one convenient place. I could buy a set of factory amp bypass cables to allow the tube amps to basically plug in. I will have to verify, but I believe the speakers are 6 ohm, but that would just change the OPT design to pick.

What I'm thinking....

- The little edcors should probably work nicely given the lack of need for low bass amplification
- The solid state amp can remain and power the sub
- Amp will be in the trunk, with a proper cover to prevent impact
- I want this to be SE, both for audio and the number of tubes and other parts to make it PP would be prohibitive.

What I don't know....
- What sort of tubes were used in common car stereos, due to rugged construction and obvious limits on power supply design (or other tubes that would work well, also). Guessing NOS is the only way to go here.
- Can I get enough power from the electrical system to run 4 tubes with a 10-15W UL output? The alternator is good for 130A....more than a number of cars, so that might help...
- Do I need a custom P/S or transformer for the HV?

So, with that said... please bash / encourage away as you see fit. I'd like honest feedback about this idea :)
 
You can use one of the SS car amplifiers you've got to power the powersupply for the tube amp. A wien bridge low distortion oscillator can drive the SS amp, which in turn drives a step up transformer. A reverse connected line tranny of appropriate rating should work. Now you have high voltage and can use any tube you want.
 
I want to build one in the future.
You can mod a car PS to give you the high voltages or construct your own.
I'm saving some 7C5 for this amp. They are loctal 6V6 and where used in car radios.
I want to use the unity coupled topology, as McIntosh use, getting high power with low idle current, but the OPT are the problem as they are not ready for purchase.

Diego
 
I've posted to this effect before, but there are tubes designed specifically for this purpose. I'm thinking the 6GM8, which is intended for low-B+ operation in the range of 24V. I haven't heard one personally, and I only have a rough idea of how linear it is at these low voltages, but it seems pretty popular of late.

Obviously, this doesn't fit the needs of an output stage (being a signal tube), but you may have good results driving a more car-friendly SS power amp with it. That'd absolve you of having to generate more traditional B+ voltages from a 12V source.

--k
 
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