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Tube SPL
Tube SPL
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Old 11th June 2003, 06:08 PM   #1
Petman is offline Petman
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Default Tube SPL


I have this question: I would like to show some silicon guys in car tuning shows that a tube amp is a bomb for SPL.
Since it doesn't require hi-fi, what would be a good setup, in terms of schematic and tubes used, etc?

Many thanks
"and the music plays forever" - Pet Shop Boys
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Old 11th June 2003, 06:30 PM   #2
Joel is offline Joel  United States
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I can't make any sense of your question. Are you saying you want a very loud, bad sounding amp???

If so, find your nearest Sony dealer.
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Old 11th June 2003, 06:51 PM   #3
analog_sa is offline analog_sa  Europe
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Show the silicon guys you won't. But they'd be laughing their heads off.
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Old 11th June 2003, 07:44 PM   #4
Positron is offline Positron  United States
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Default Here goes

Here is one way, but you are going to have to spend some money. I, in no way endorse this product, or its performance.

Get a 12 DC to 120 VAC inverter, preferably 2000 watts or so.

Get 4 of 4cx250bs for stereo PP operation. Now you will need a power supply to go from 120 vac to approx 2000 to 2300 DC volts.
You should get approx 650 watts/chanel RMS out of this critter.

The OPT, gain stages, blower cooling etc. are up to you.

Have fun with this baby.
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Old 11th June 2003, 09:16 PM   #5
Colt45 is offline Colt45  Serbia
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get a whole shitload of 6080's/6AS7's, and run 'em in OTL.

you can run the filaments right off the battery, but youll need a 12v : 100...150v DC-DC converter for B+
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Old 12th June 2003, 04:32 AM   #6
Positron is offline Positron  United States
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Default More power?

Some in CB run 4 or 5 alternators and use 4cx15000 tubes.

If you run about 10kv or so, in PP you'll get some 57kw output in AB1.

Could try a 4cv50000E, but need water cooling, but get 195kw output in AB1.
Need 15 kv, 18.6 amps. 12 volts at 215 amps just for the filaments.
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Old 12th June 2003, 08:06 PM   #7
PRR is offline PRR  United States
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> <i> a tube amp is a bomb for SPL.</i>

A bomb for loudness, perhaps. Not a bomb on the SPL meter.

Assuming you hold distortion to not much more than 10%THD, the SPL meter will read about the same as the power meter. 100 watts is 100 watts to an SPL meter. If you let distortion rise higher, it may read higher, but the solid-state boys know that too. I thought good SLP competitions had some control of distortion so it wasn't all square-wave melt-down testing.

A large tube amplifier rarely beats 40% total power efficiency on sines; most any tranny amp does 60% at clipping. This means you need 50% more battery and alternator to feed the tubes to get the same power. And I'm assuming you get the high voltage without massive cost or loss.

An inverter is an off-the-shelf way to get HV out of 12VDC. The outside-the-box way:

The voltage out of an alternator is proportional to RPM. They make 12V at 600RPM, but 120V at 6,000RPM. Normally a regulator reduces the field current to hold them down to 13-14V at high RPM, but assume we bypass that (easy).

Alternators make AC. You think they make DC because they have rectifiers, but you can tap inside the case and get the AC.

In high-power car-sound competition, there are custom alternators everywhere. We'll assume an unrectified unregulated alt-hack.

A heavy-duty 12VDC alt to feed the heaters, radio, lights, etc, and a second alternator just for the HV.

If we further assume that you can un-belt the HV alternator while on the highway, and belt it for competition, you can over-gear the alternator to give 100-150V AC at a reasonable 1,800 fast-idle. (I assume the loud-heads show-off their rigs at fast idle: there are 10,000 watt cars and a mini-engine does not have that 14 horsepower to spare at 600RPM slow-idle.)

So we have 100-150VAC at 50-200Hz. We can run that through a simple transformer to get even higher voltage. No solid-state inverters. Actually we'll need 3 transformers because an alternator is 3-phase, but the sum-size of a 3-tranny bank is smaller and cooler than a single-phase transformer of the same load.

So three 120VAC:3500VAC transformers into a rectifier/cap directly give us 5,000VDC, which will power transmitter tubes. That's the only sane way to get kiloWatts out of tubes, unless you really want to see acres of bottles. (Yes, 500VDC into 4-dozen 6L6 would look kewl too....)

You need an audio transformer (OTL is possible but the overall efficiency on speaker-load is really horrible up into the kiloWatt area). Since car-sound fans really love their subwoofers and push them to low frequencies, you can't get too skimpy. A kiloWatt transformer for 30Hz is <b>BIG AND HEAVY</b>. Hundreds of pounds if you want deep bass. To keep up with a fairly modest (in competition) kiloWatt transistor amp, your car springs will sag.

And the 50% drop in overall efficiency, at the kiloWatt level, is likely to melt your headliner. Nevermind that: it may soften your Door Seals, which are Critical to high-SPL car-competition. Don't let that bass out!

In short: I think a fully-tube competition-level car-sound system is going to cost too much, use too much space, and may be unable to drag itself around town.

What makes more sense: get/build a couple Bogen 100-Watt tube amps, inverter-powered, just to feed the front midranges. It will sweeten-up a critical part of the sound, You can hide all the sand-state amps under the tube amp, so it looks "all tube". When you tire of the joke, you can put the tube amp in the home where it belongs and still have a thumpin' car.
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Old 12th June 2003, 09:06 PM   #8
Gabevee is offline Gabevee
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I've got news for you... I hooked up my 15 watt p-p tube amp (only one channel!) to a pair of 12 inch boom box woofers in a car (I used a 300 watt 12VDC to AC converter. BTW). It performed as good as the guys 600 watt S-S according to him, not me. I was surprised that it put out all that bass at all! Amazing. For nothing but bass, it works fine, especially if the woofers are 98dB SPL for 1 watt. As for distortion, since it is mostly 2nd harmonic, it will make the perceived sound louder.

Of course, after I modded his SS amp ($12 op-amps, thick wiring from power supply and outputs, etc), it blew every other amp away.

If you get a 40-60 watt P-P tube amp, you will get strong results, to be sure.


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