What is the most powerful audio output tube?

The output tranny required for 500 watts RMS is going to be a huge piece of f*ck-off iron that will probably set you back the better part of a grand, at least.

500 watts RMS from four tubes will require you to step up way beyond 6L6es and 807s, I think. You're probably going to want to look at something like RF power triodes or tetrodes, 813s or the GU-13 if you're okay with going ex-Soviet.

I am not a pro tube guy though so that's just my guess.

807 is the transmitting version of 6L6, so it's no wonder that it looks similar.

For the power level you're after, you may need real transmitting tubes, e.g. a pair of 3-500Z's. Please understand that the voltages and currents encountered at those power levels will be lethal in careless hands.

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-TV

Go big or go home.

boomer# snipped-for-privacy@none.com prodded the keyboard with:

Have a look for a Trix cinema amplifier, they did one that used a pair of 813's at around 500 W rms 100 volt line out.

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Best Regards: 
                      Baron.

first hit on google for 500w tube amp

On 12/08/16 07:19, boomer# snipped-for-privacy@none.com so wittily quipped:

you'd probably do well with 6550, or KT88 (or maybe 8417 if you can find them) - I think you'd need 6 of them for 500W. Output transformer might be a bit more difficult.

this page shows the 1650W for 280W and 6 to 8 output tubes

if you're desperate, you could just bridge two of them to get 560W, or tweek the circuit and use the 8 ohm output on 4 ohms and run the risk of frying the transformer at some point...

You want a pair of 6427's like WABC used to run

(RMS watts is a misnomer)

m

The maximum plate dissipation of a 813 is 100 W, which is a bit too little for continuous 500 W out. 4 * 813 will stand 400 W on plate, but 2 * 3-500Z will stand 1 kW.

--

-TV 

PS. Been there, done that. I still have a scar due to a transmitter 
built with 813's.

...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| STV, Queen Creek, AZ 85142    Skype: skypeanalog |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
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             There is no fool quite like an audiphool.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

The transformer is the problem, especially if you go with a giant transmitting tube that runs at high plate voltages.

There have been transformerless audio power amps, using that beast low-mu triode tube, the one Tek used in their B+ regulators.

Why not use mosfets? Toobs are silly.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

AM Radio stations used some that would do 50,000W, I believe. Is that sufficient?

You don't want the "most powerful" tube -- you just want one that fits your wimpy (relative to "big radio") requirements.

If you're serious about this, get this book. It'll provide hours of drooling entertainment if you're just a fanboy, so it'll still be worth it:

There are a lot of tubes that will do your job that are both in that book and available.

The 1625 is basically an 807 with a different base and a 12V filament -- all other ratings are the same. It's much cheaper than the 807 from tubesandmore.com. Eight of them (enough to do 500W) is cheaper than a pair of 813's, and they'll run at a much less lethal plate voltage.

A pair of 4-1000A tubes would be dandy, but I don't know where to find them (I'm a fanboy, not an expert).

Note that ALL of the tubes I'm mentioning here are radio tubes, not audiophile tubes -- if you judge an amplifier by more than how hot it gets and how much it costs, you may not be happy with the sound.

--
Tim Wescott 
Control systems, embedded software and circuit design 
I'm looking for work!  See my website if you're interested 
http://www.wescottdesign.com

Scan available for free at

(although the price of the Tubes And More reprint is an excellent one!)

The application tables for AF power amplifier and modulator service start on page 88. The 7650 and 833A seem to be the brutes of the lot.

4CX1000A and friends are more fussy to handle than the glass-envelope toobs, and an audio amplifier does not need the minimal-RF-impedance structures of the external-anode ceramic tubes.

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-TV

Yeah, not to mention the "instant death" ~1.5kV supply and cap bank that would be required to feed such a beast.

I think that's the 6080/6AS7. I saw a 50 watt OTL amp that used something like 8 or 12 of 'em in push pull parallel to hit that.

I can't even imagine what you'd have to throw at that topology to get 500.

An OTL headphone amp using say a single 6N7 power triode for each channel and something like a 12AU7 used as a diff-pair gain stage would be a nice weekend project for maybe half a watt per channel - way more than required.

You can drive MOSFETs or tubes of the same polarity stacked totem-pole from a tube diff pair, but the driver design has to be a little clever to equalize output impedance and gain between the stages:

I'd question my sanity if I started thinking about a 500 RMS watt all-tube amp though. Well, this guy actually did do something rather crazy:

Output transformer looks like it weighs about as much as I do.

Eimac's 'The Care and Feeding of Power-grid Tubes' is also very good, if it is somewhere to be found.

For Class-B push-pull a pair of zero-bias triodes is much easier to handle, e.g. 3-500Z or 3-1000Z. The kilowatt tubes are a bit of overkill for 500 W output.

Right - the big tubes are classified as transmitting tubes even when they are used in high-level AM modulators (where IMHO the biggest audio outputs are used).

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-TV

There's not nearly enough protection on that monster for my liking, either. If I were crazy enough to build something like that I'd probably have a dedicated uP on every output tube monitoring all the voltages/currents of interest and shutting everything down quickly if something looked amiss.

Those transformers don't look cheap.

The last toob in that list (1MW) has the comment "the ultimate tube for QRP" so I'm guessing this person doesn't know his Ps for his Os. Unless he's aiming for ultimate sarcasm.

Cheers, James Arthur