tube amp for automobile / need ideas

[jmillerdoc]

Hi,
I have been a newbie in tubes for about 11 months now. Although I have learned a ton, most of you that have helped me have probably forgotten more than I have learned in the past several months.

I have built a couple of tube amps to include the KT88 Oddwatt monoblocks (from scratch), a K-502, several Gainclones including the JLtI valve buffered version, and sever tubed preamps from schematics and one of my own design.

My father, who just turned 63, has been intrigued with the results of my hobby. He has a much more expensive one, rebuilding classic cars. He is in the final stages of restoring a '57 Chevy 2D HT Belair. He mentioned the other day that he thought it would be neat to build a showy tube amp that could be mounted in the trunk to run the stereo he has plans to install.

Now for the question I have been leading up to.....can a tube amp be built for a 4 channel automobile system? I am sure it can be done, but is it feasible? I have thought of doing a valve buffered gainclone type of setup but it wouldn't really have much to "show off" for a show car. I was thinking more in the lines of a fairly large chassis with x4 OPTs and a complement of 8 to 16 tubes running a PP set up. I could probably use some sort of power inverter to get 115VAC from the 12V system but I was wondering what it would take to build an amp using the 12V sustem directly with some sort of voltage multiplier and a tube type that might work on a lower than usual B+ (I wouldn't have a clue of which tube could fit the bill here).

Is there anybody out there that has any experience with automobile systems based on tubes? I would want to target around 10-15wpc. I would probably use Fostex or similar high sensitivity drivers a with a SS amp running a small hidden sub. What would be best is a schematic for a proven amp that was built for a car. Second best is just some good old direction and help with creating it de novo.

My last option would be to reproduce the JLtI valve buffered gainclone using a voltage double/tripler for the supply, but again, there wouldn't be much to show off, just maybe 4 tubes in a small enclosure.

Thanks!
Jeff Miller
Lawton, OK

[aardvarkash10]

Bob danielak has done it... "Auto-Darling" SE 1626 Tube Amp for my CAR!!!

[aardvarkash10]

I'd add that the Fostex are not a clever option. Car audio is designed for cars, and good car speakers are significantly different to those for use in your house. The frames a stronger, the sensitivity is waaaaaaay lower and they are built to produce sound in a manner that matches the common characteristics of a car interior - lots of soft edges, wind noise at particular (frustratingly mid-range) frequencies, NHV including tyre noise, suspension etc. In short, Fossies are unlikely to last long, or sound any good in a car...

[DigitalJunkie]

I've been planning something for my '67 Chevelle for years now...I finally dug out an old 300W inverter that had fried FET's in the H-bridge/chopper section,and added a voltage doubler right off of the transformers secondary.IIRC it makes right about 300V with a decent load on it. Of course,you could just put a doubler on the output of a bone-stock inverter and get a similar voltage from it.

Besides HT power (heaters are easy,some linear/switching reg's will work nicely) I think the next big obstacle is some kind of vibration/shock proof mounting system. Your poor tubes might get vibrated to death on a rough road,or after a pothole or two.Not to mention microphonics. I haven't come up with a decent solution for that problem,yet.
Maybe some kind of spring suspension for the tube chassis,along with ample use of silicone damping O-rings for mounting everything...dunno.

[ChrisA]

Originally Posted by jmillerdoc

Hi,
.....can a tube amp be built for a 4 channel automobile system? I am sure it can be done, but is it feasible? ...

Can it be done? Car radio pre-dates the invention of the transistor. There were even tube based two way radios used in police cars, the military and hams.

The range of tube using 12V heaters were designed so that the heaters could run off a car battery. Using 12V heater tubes solves most of the power supply problem. All you need is a B+ supply.

The easy way is to get a "true sine wave" inverter and then run the amp off 120VAC but I think the old radios designed the inverter into the radio and derived the B+ power direct from the 12V DC.

[aardvarkash10]

Originally Posted by ChrisA

The range of tube using 12V heaters were designed so that the heaters could run off a car battery. Using 12V heater tubes solves most of the power supply problem. All you need is a B+ supply.

...as were the 6.3 volt heaters before them from the days of 6v car systems...

The easy way is to get a "true sine wave" inverter and then run the amp off 120VAC but I think the old radios designed the inverter into the radio and derived the B+ power direct from the 12V DC.

Inverters were typically vibrator units and separate from the radio itself. Old valve Car radio. for sale - TradeMe.co.nz - New Zealand

[Glowbug]

Car audio is designed for cars, and good car speakers are significantly different to those for use in your house. The frames a stronger, the sensitivity is waaaaaaay lower and they are built to produce sound in a manner that matches the common characteristics of a car interior - lots of soft edges, wind noise at particular (frustratingly mid-range) frequencies, NHV including tyre noise, suspension etc. In short, Fossies are unlikely to last long, or sound any good in a car...

I know of a couple people running FF85Ks in their dashes replacing the stock 3" drivers...not to mention all the people I know using "home" drivers (Seas Excels/CAs, Peerless, Vifas, etc). No reliability issues.

As for the 12V tube amp idea, I really want to hear DD's EL34 beast: http://www.audiojunkies.com/blog/463...tube-amplifier

I don't know if 10-15 watts is honestly going to be enough for the entire front stage, unless you use horn-loaded compression drivers. Which would be kick-*** for a show car install

[aardvarkash10]

True glowbug ...not to mention that if its a "show" car its unlikely to get the sort of treatment that a daily driver has to put up with...

Imagine a compression driver horn, winding its way around the inside of the trunk like a cross between a python and a tuba!

[Geek]

Originally Posted by Glowbug

I know of a couple people running FF85Ks in their dashes replacing the stock 3" drivers...

What a sweet idea!

About all the room my Aspire has for too

Cheers!

[Glowbug]

Another plus for HLCDs would be the space you've got in a car like that...no problems stuffing them under the dash, I'd imagine. And 10W would scream, all you'd need is another 2 channels (50-100W) for the midbass drivers.