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Author Topic: Tube Amp Wattage Theory question  (Read 220 times)

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ducatidoc

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Tube Amp Wattage Theory question
« on: July 31, 2019, 07:53:24 pm »

This is a question that I constantly keep musing over.  AFAIK, the most powerful commercially available tube-powered instrument amplifier is/was the Mesa Bass 400+.  Assuming you wanted one single head with as many speaker cabinets as needed , what would be the most powerful tube amplifier attainable, built by using currently available components, taking into account weight, size, portability, and most importantly , musicality ?

Reason I ask is I?ve always thought that the 2000S represented the pinnacle of what Sunn could achieve using ultra linear OTs. That is, if you wanted to maintain <1% THD.  Could you achieve 130db or more by doubling up on the transformers ?  Let?s assume a max chassis weight of 200#. Electro-gurus opinions welcome.  I have way too much time on my hands.

EdBass

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Re: Tube Amp Wattage Theory question
« Reply #1 on: August 01, 2019, 07:35:20 am »

There are more powerful amps than the 400+ on the market. An Ampeg SVT is more powerful than the discontinued Mesa 400+ was, Hiwatt and Reeves 400's are, and I'm sure there are others that escape me. Kind of a moot point though, with modern sound reinforcement gear there's not a lot of need for huge heavy tube amps anymore; just stick a nice mic on it and run it through the PA.
There have been, and currently are projects for mega amps for decades. Here'e a 1000 watt Philips amp from 1955;

https://www.youtube.com/watch?v=btSg2SX3lUs

Google will find you plenty of projects like that. Not sure why anyone would WANT 130 db out of a bass amp, any stage I've been on that would cause someone to shut it down immediately, however with enough efficient drivers in efficient boxes you could probably get 130 db out of a 2000S.

ducatidoc

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Re: Tube Amp Wattage Theory question
« Reply #2 on: August 01, 2019, 08:15:58 am »

Actually, my curiosity is just hypothetical. A few of my questions are addressed in the comments section of that YT video. You're right about the practicality of a 130db amp; I certainly wouldn't want to attempt it either.  I've always assumed that the limitation on power is related to the capability of the output transformer. I guess the chief question is how much output can you achieve from a tube output section in less than 200# and how would you strategize the design ?

EdBass

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Re: Tube Amp Wattage Theory question
« Reply #3 on: August 01, 2019, 12:12:28 pm »

Theoretically, aside from practicality, the likely physical limitations would be current to the power supply, transformer mass and heat dissipation.  The "practicality" restriction would kick in pretty quick I would think, somewhere around the size of an SVT... :wink: 
At what weight/mass/heat would it require a dedicated and permanent installation?

Happy Face

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Re: Tube Amp Wattage Theory question
« Reply #4 on: August 01, 2019, 06:48:32 pm »

Why not just use two or three amps instead?

The added bonus is redundancy if one fails during a show.

Mmmm, best to have an additional head in the van as well. 

ducatidoc

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Re: Tube Amp Wattage Theory question
« Reply #5 on: August 02, 2019, 01:07:05 pm »

I think I made the question too broad, whereas the thing that got me started on this train of thought was a Conrad interview I watched (don't remember which one), wherein he was talking about the late '60's amp scene and made reference to "everybody was going for bigger and louder". Solid state tech at the time wasn't reliable enough, so they were stuck with tubes (notwithstanding the SS rectifiers that were gradually being swapped into their design). I have always maintained that 120-150 watts was the max he could get at the time, with tubes, if he wanted to maintain the hi-fi standard, and this was related to the unavailability of larger ultralinear transformers.

So the 4 x 6550 amps were, for a time, the loudest available production amps, assuming you wanted to maintain <1% THD across the spectrum. I think it's fairly well known that Sunn was the only major amp mfg to use ultralinear OTs, and that's how they achieved that std.

So.... could we beat that today, with a tube power amp design, in less than a 200# chassis ? Let's suppose we want to base it around a 2000S-type circuit, and end up with a similar style head, albeit up to 120# heavier.  Assume your roadies are ex-NFL lineman.

And again, I don't want to try anything build-wise. It's strictly hypothetical.  A chance to think like a Sundholm.
« Last Edit: August 02, 2019, 01:18:59 pm by ducatidoc »

EdBass

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Re: Tube Amp Wattage Theory question
« Reply #6 on: August 03, 2019, 01:17:00 pm »

I don't think it would have been a problem for Sunn to scale up the 2000S to a 6 X 6550 or an 8 X 6550 and maintain the ultralinear Hafler/Laurent Dynaco circuit. As far as transformers, all that needed to be done was to commission a transformer builder to make them.
Interestingly enough, that almost had to be the case when the 1000 series amps were produced in 1968. While the 100 series Sunns were pretty much dead on the Dynaco circuit, including "Dynaco Super Fidelity" transformers, there WAS no Dynaco 4 X KT88/6550 amp, therefore no Dynaco Super Fidelity 4 X KT88/6550 transformers until 1976, 8 years after the Sunn 4 X 6550 amps were introduced.
In 1969 the SVT came out, and pretty quickly (and deservedly IMO) became the King, still is 50 years later.
Mr Sundholm sold in 1971, and I certainly can't speak for him however I'm sure if he were so inclined to make a 300, 400 watter using the Dynaco circuit he could have, and doubt that unavailability of larger ultralinear transformers would have presented a serious challenge.

As far as the <1% distortion, (as with the rated output) that's somewhere around "3" on a Sunn's volume knob. The reason that Sunns were renowned for being "loud" amps is because the were rated so low; in the actual MI world no one played them at "3". A 2000S is a solid 200+ watt amp in a live situation, one of mine that was retrofitted with a SDS Cap board benched in the 220-230 range at around 5% THD, peaks north of 280. 5% is a usable "clean" for live use, <1% is hi-fi world clean.
Bass Gear Magazine lab tested a Reeves C225 at 256 watts, 5% THD, they did it right, that's a solid rating. I A/B'ed a C225 next to a 2000S for literally dozens of hours during the development of the Reeves, the Reeves is more powerful - but not by much. Certainly not a 225 watt amp being A/B'ed with a 120/150 watt amp "more powerful".

As far as your theoretical question, well, you need to build one and let us know the answer.  :-D
One thing I am sure about is that no  amp company is going to build a 200lb amp, there is absolutely ZERO chance of ever selling them, and they are not about to expend any effort or $ even researching such a beast.