A friend of mine has VTL 750s (biamped, no less) and they sound wonderful. They're extremely reliable as well. VTL also makes a 1250 Watt version:
VTL - Reference Monoblocks
It's not as unreasonable as you think. You could get close to a thousand watts with just two GU-81M in class AB1 push-pull pentode.
GU-81M GU81M GU-81 GU81 ГУ-81М Power TUBE Ham,Pentode - eBay (item 260538309935 end time Feb-14-10 07:35:14 PST)
John
VTL - Reference Monoblocks
It's not as unreasonable as you think. You could get close to a thousand watts with just two GU-81M in class AB1 push-pull pentode.
GU-81M GU81M GU-81 GU81 ГУ-81М Power TUBE Ham,Pentode - eBay (item 260538309935 end time Feb-14-10 07:35:14 PST)
John
Thanks to everyone for the responses.
The 813 are not really an option for me, just due to the plate voltage needed. I think thats a little bit out of my league.
Very interesting points about the power. I dont think Id ever take my amp to a soggy field in Somerset, plus I cant imagine many ravers would care that they are listening to a valve amp
Part of my work involves festivals and 3 phase power is always readily available.
Solid State is clearly the more ideal way to go. But unfortunately my mind is set on it now so no going back
The 813 are not really an option for me, just due to the plate voltage needed. I think thats a little bit out of my league.
Very interesting points about the power. I dont think Id ever take my amp to a soggy field in Somerset, plus I cant imagine many ravers would care that they are listening to a valve amp
Part of my work involves festivals and 3 phase power is always readily available.
Solid State is clearly the more ideal way to go. But unfortunately my mind is set on it now so no going back
Wow. Are you in for a ride. Sound reinforcement is obviously a bigger mountain than you have any idea about.
What is the point of all this anyway? Even if you can make a case that tubes offer a better sound than solid state under ideal listening conditions, the environment you intend to entertain is anything but!
How many people, if they could even detect a difference, would care in that environment and why would you pay 5 to 10 times the price of a used pair of 500 Watt solid state amps just to entertain them?
You would be better served to put money into the speakers, which are the weak link of any sound system, and focus on correct equalization and SPL levels.
Personally, I would consult a professional sound reinforcement company or individual and let them handle the event or at least consult on what to do.
Solid State is clearly the more ideal way to go. But unfortunately my mind is set on it now so no going back
Get a quote for a 1kw output transformer before you make remarks like that
316a
About 20 Years ago we were running a PA system on a motorrace TT circuit in Assen The Netherlands. Because the very long cables connected(induction) and problems with thunderstorms, transistor amps would not last very long. Today everything is well protected and we are using sand-amps with no trouble.
To get a very reliable ampiflier(when you have an event the show must go on) with tubes we had 3 stacks of 40 EL34 pushpull amps in parallel.
So when an amp broke down you could pull out that amp and replace it.
The event lasted 5 days and someone was repairing all the time.
For 35 years ago I build a 1200 watt PA amplifier see Amplifiers with valves
The amplifiers still works.
The amplifiers still works.
Of course you can. All you need are a couple of high power RF finals, about 3.0KV @ 1.0A to run 'em, and stainless steel cojones. Max legal ham rigs run about that much. Of course, this is going to require considerable care, since with a power supply like that, you won't get a second chance if you screw up once.
(This also applies if you decide to go the solid state route.)The big sticking point is going to be the OPT. With RF, it's NBD since you're dealing with a very narrow band of frequencies, and the doubly tuned OPTs used here can be wound with air cores and just a few turns of copper tubing. For audio, it's going to be a formidable challenge to get an OPT that can handle 1.0KW, and maintain some reasonable semblance of fidelity. That's going to cost $Lotsabux.
I think the low voltage/low impedance approach is more practical than high voltage/high impedance transmitting tube approach. Having said that, my current project is a 300W+300W amp using 1500V B+ and 4CX250 transmitting tubes (I'm forced into it by the large high-impedance OPTs I acquired...)
I'm no transformer expert, but what I know suggests that lower impedance OPTs are easier to build at the power level you're contemplating.
VTL are using a very practical approach. Parallel the number of 6550s you need in AB1 and wind the OPT to the required primary impedance. You could get a little over 1KW total using 4 monoblocks with 6x 6550s each and an OPT like the Hammond 1650W (only 28 lbs). The whole ensemble would probably weigh under 500 lb. ready to transport. Using SMPS for the B+ and g2 supplies could save you about 1/2 the weight.
Nice listings of high-power tubes with datasheets here: G8WRB (plate dissipation from 100W to 1MW).
There's some real monsters there. e.g. this THING - a tetrode designed for high-speed switching - typically 50A @ 120KV
Makes me wonder about the possibility of a high-power, valve-based class D amp, though.
Anybody ever tried a class D valve amp?
There's some real monsters there. e.g. this THING - a tetrode designed for high-speed switching - typically 50A @ 120KV
Makes me wonder about the possibility of a high-power, valve-based class D amp, though.
Anybody ever tried a class D valve amp?
Well I think thats quite a negative out look. Compared to most here I am relatively new to amp building, but that doesnt mean I dont know what Im in for. And my questions are innocent and not immature.
The point of it all is to start a conversation with people who really know what they are doing, and gain a valuable insight on the matter. And its working so far...
Even if 1 out of 100 people commented on the sound, I think it would still sound amazing. And thats all that matters to me..
No, your questions are not immature, but they are naive.
Even when tube PA amps were common, a distributed approach, i.e. 5 x 200W would have been a more likely solution than a 1000W monobloc (or two).
It's a romantic idea, but it won't achieve a notable sound quality, and it's environmentally unfriendly (not green).
w
Even when tube PA amps were common, a distributed approach, i.e. 5 x 200W would have been a more likely solution than a 1000W monobloc (or two).
It's a romantic idea, but it won't achieve a notable sound quality, and it's environmentally unfriendly (not green).
Bob Dylan; said:
w
Aha, shame on me for not appearing in this thread sooner. What would I do? Around 600VDC supply into four of the largest sweep tubes you can find (e.g. EL519?).
Tim
It is not negative, but an observation based on the comments of your original post.
Bluntly, it appears as ignorance. I don't mean that in a condescending way, so please do not take this as an insult. It is not!
Simply put, sound reinforcement is not a trivial subject and while I have a little knowledge on the subject, I have enough of a grasp to know just how deep the forest is.
When you pop in here and say I want to build a 1kW amp for a PA system some questions come to mind, mainly, what are the real requirements driving this?
Not that there isn't a good reason behind any driving reason, but it would be helpful to state exactly what you need so we can help guide you to a solution that best fits the needs.
If building a 1 kW amp is something you want to do just to climb that mountain, that is fine. However, if you are looking for the best approach to provide sound reinforcement for a specific theater or situation, then you may have skipped a few steps in your assumption that a single 1 kW tube amp is the best solution. This is the heart of my question. How did you arrive at this solution and what other solutions have you considered? What are your most important requirements and why?
They may seem like pointed questions, and they are, but critical questions are key to arriving at the best solution (be it scientific, engineering, etc.). It's not personal or emotional at all.
Since there are several differing opinions already posted here, I will add mine. It comes from my limited experience with outdoor rock concerts. Today it is possible to buy a 1 to 2 Killowatt solid state audio amp for about $500 USD. For many rock groups that would be the instant solution a big SS amp and 4 or 6 speaker cabinets. Cheap (relatively) but lousy sound. How do you do better?
Do what the sound reinforcement pros do, on a smaller scale. Bi-amp, or Tri-amp. An adjustable crossover network splits the sound into 2 or 3 frequency bands. Each group of frequencies is routed to its own amp and speaker system. The amp and speakers are designed for the band of frequencies it receives. This allows for a good deal of flexibility to tune the system for specific venues
You didn't specify the size of the venue, but 1000 poeple at a rave inside a packed warehouse is a bit different from 1000 people scattered in a field. Either way you need a set of speakers capable of filling that area with bass. The number and type of cabinets vary with the venue. Box type cabinets for indoor use, and horns for outdoors if there is space for them. These bass speakers need to be fed, and they are hungry. The bass cabinets need 3 to 5 times the power than all of the other speakers. I hate to admit it but a solid state amp makes the most sense here. It doesn't even make sense to build one (unless you want to play with those new class D chips from TI) when you can buy one cheaper than you can build it. The bass amp needs to have a high damping factor to get tight bass with many speakers. This isn't easy with a tube amp.
You will need another set of speakers for the rest of the sound (roughly 500Hz up) and an amplifier to run them. This is where you want your tube amp. It does not need to be 1 KW either. I would guess that if your bass amp is 1 KW, the mids / highs amp should be about 300 to 400 watts. Now an output transformer that can do 400 watts from 500Hz to 20 KHz can be held in your hand. A transformer that can do 1KW from 20 Hz to 20 KHz will be about the size of a microwave oven. You can build this amp. Plitron or Amplimo sells 400 watt toroidal OPT's that will actually cover 20 Hz to 20 KHz at 400 watts. I got a pair. Wire up 6 or 8 KT88's and a big power supply.
Do what the sound reinforcement pros do, on a smaller scale. Bi-amp, or Tri-amp. An adjustable crossover network splits the sound into 2 or 3 frequency bands. Each group of frequencies is routed to its own amp and speaker system. The amp and speakers are designed for the band of frequencies it receives. This allows for a good deal of flexibility to tune the system for specific venues
You didn't specify the size of the venue, but 1000 poeple at a rave inside a packed warehouse is a bit different from 1000 people scattered in a field. Either way you need a set of speakers capable of filling that area with bass. The number and type of cabinets vary with the venue. Box type cabinets for indoor use, and horns for outdoors if there is space for them. These bass speakers need to be fed, and they are hungry. The bass cabinets need 3 to 5 times the power than all of the other speakers. I hate to admit it but a solid state amp makes the most sense here. It doesn't even make sense to build one (unless you want to play with those new class D chips from TI) when you can buy one cheaper than you can build it. The bass amp needs to have a high damping factor to get tight bass with many speakers. This isn't easy with a tube amp.
You will need another set of speakers for the rest of the sound (roughly 500Hz up) and an amplifier to run them. This is where you want your tube amp. It does not need to be 1 KW either. I would guess that if your bass amp is 1 KW, the mids / highs amp should be about 300 to 400 watts. Now an output transformer that can do 400 watts from 500Hz to 20 KHz can be held in your hand. A transformer that can do 1KW from 20 Hz to 20 KHz will be about the size of a microwave oven. You can build this amp. Plitron or Amplimo sells 400 watt toroidal OPT's that will actually cover 20 Hz to 20 KHz at 400 watts. I got a pair. Wire up 6 or 8 KT88's and a big power supply.
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