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Old 21st December 2009, 05:33 AM   #1
Luke352 is offline Luke352  Australia
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Default Tube pre-amp for a vehicle?

HI guys not sure if I should have posted this here or in the Tube section, but in either case I 'm sure a mod can move it for me if I have posted it in the wrong place.

As the title says, I'm interested in build a Tube Pre-amp/ gain stage for my car, I'm just interested to see what results I'll get and also for a bit of fun to keep myself occupied.

I have my current HU that has up to 5v pre outs, and then off it goes down my RCA's to my amps, which have there own pre-amp section with variable gain controls, so I don't need this Pre-amp to have volume as a part of it's design or to have much actual gain, infact straight through up to maybe a 2x gain would be perfect as a little boost to the signal voltage wouldn't hurt. Basically I just want to experiment and see what sort of results I get by adding a bit of tubey goodness to the signal.

So can anyone suggest some designs or kits that would be able to work off a 12v power supply and that are fairly simple in design and low gain.

Thanks Guys and Gals.

Luke
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Old 21st December 2009, 05:42 PM   #2
gfiandy is offline gfiandy  United Kingdom
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Tubes and vibration - not a good combination. If you want the tube sound in a car I would look at a FET based tube simulation.

I guess it depends on how reliable you need it to be and how much you are prepared to spend on replacement tubes. I don't really know how well tubes will survive in this environment, I know they were used in early car radios. That might be a good place to look for inspiration for designs. Unfortunately I have no car tube circuit diagrams.

Regards,
Andy
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Old 21st December 2009, 09:39 PM   #3
Luke352 is offline Luke352  Australia
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Yeah vibration will be an issue I'll admit, but there are several amps on the market that use Tube Pre-amp sections, so I figured the vibration issue can't be too bad, aslong as I can mount them in a shock absorbing setup.

I guess for initial trial it won't have to be too reliable but if I like what I hear I'll invest more time into making it more resilient to vibration and shock.

I figured something like this 12AX7 Tube (valve) Preamplifier Kit would be ideal if modified to use a 12V-14V DC supply rather then the 17V power pack it is designed for. But then the issue becomes how resilient will the design be to a DC supply voltage that will swing from around 12.5-13.8 volts.

The other issue with that design is it has a 4x gain, I only want 2x - 2.5x at an absolute max, I also can't find the kit on the SC online shop. I'm sure it could be modified for lower gain , but that is beyond my abilities, I can solder and understand what symbols and values mean on a circuit diagram but as to understanding how a design works that is still beyond me I'm afraid,
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Old 21st December 2009, 10:41 PM   #4
gfiandy is offline gfiandy  United Kingdom
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At the end of the description on the link you listed it says the kit is out of production. You could point to point wire the valve section but the switch mode will not work unless its layout is just right.

I would take your question to the valves forum where you will probably get much more help.

Andy.
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Old 21st December 2009, 10:56 PM   #5
Luke352 is offline Luke352  Australia
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Ah I must have missed the bit about being out of production.

Thanks for your help! Of to the Valve section I go.

Thanks

Luke
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Old 8th September 2010, 02:26 AM   #6
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Vibration will not be a problem, especially with the kind of tubes you would be using in this application. Soviet fighter jets use vacuum tubes for radios and radars right to this day, and they do so because they are both more powerful and not subject to EMP (from nuclear blasts nearby).

A car might be a high vibration environment, but aircraft are an order of magnitude worse. There may be issues, but this isn't going to be one of them. If you're really worried, use a military-grade tube, built exactly for such an environment.
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Old 8th September 2010, 03:03 AM   #7
Pano is offline Pano  United States
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Johnny - you realize you just did a Lazarus, yeah?
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Old 8th September 2010, 08:30 AM   #8
gyro is offline gyro  United Kingdom
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Take a look at the specs for old russian 6n1p-ev / 6n2p-ev tubes. Linear accelerations of 100-150g, vibration 5-10g, multiple impacts 150g, single impacts 500g!

Rather higher ratings than the pilot!
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Old 8th September 2010, 09:11 PM   #9
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Quote:
Originally Posted by panomaniac View Post
Johnny - you realize you just did a Lazarus, yeah?
Yep ... but I just built a car preamp with a pair of vacuum tubes, and it works fine, as did radios in cars made in the 50's and early 60's, and as do units like the Milburt Car Audio Power Amp, which has a reputation for bulletproof reliability, no less.

I had a tube-based preamp driving the stereo in my truck, which never saw a paved road but often saw 70 mph, for 8 years. Pulled it, still working, when the truck finally gave up.

The examples of rugged and reliable vacuum tubes in existence, still working to this day, are numerous. Some have been working without replacement since the 1920's. There is nothing inherently fragile about vacuum tubes, regardless of any other issues for or against. In fact, just the opposite.

Had to chime in; didn't want that fallacy to sit here in case someone else did a search on the subject or a new user was poking through the threads; the topic itself is titled "Tube pre-amp for a vehicle?" after all.

Last edited by Johnny2Bad; 8th September 2010 at 09:35 PM.
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Old 9th September 2010, 01:29 AM   #10
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There are some good reasons to avoid tubes in cars such as as power dissipation and power dissipation. They burn up a lot of power, especially considering it's a preamp, and they need to get rid of a comparatively large quantity of heat. 'Course these can be minor considerations in some modern cars.

w
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