200- 500 watt Tube Amp project

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Almost no one builds tube amps this big except for a few very specialized applications, VTL builds the MB-450 which is a 450Wrms monoblock that sells at $15K a pair, and uses 8 6550 per amp to achieve this.

Given their economies of scale at VTL I suspect you would have a hard time sourcing the components to build a comparable diy amp for less than half this amount.

You can't buy off the shelf power transformers and output transformers for this sort of power. Creative power supply design might overcome the power transformer issue (several identical toroids in parallel) but the OPTS are another matter - expect to throw a lot of money at these. (Several $K)

What are you planning to drive with these that requires so much power? A smaller amp in the 100W range is probably sufficient for most home uses I can imagine.

The largest amplifiers I have ever built and sold commercial were 4 chassis 120Wrms (4 x 6550 per channel) and in the late '90s these cost about $4K per stereo pair to build.
 
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Hi All,

I'm interested in building a dual channel tube amp that can produce up to 500 w rms per channel.

But I'm not finding any schematics for my little beast. Does any one know where I might start to make the concept a reality using parts available in today's world.

thanks

One way that occurs to me is to use the 1900 ohm 280W Hammond OPT but that 475 ohm load line needs a lot of cathode current (over 1A peak). Maybe 2 or more likely 3 parallel 6550s and you could get 250W+ out. Even at that low impedance you need something approaching 600V B+

I don't know of any schematics but the OPT is the place to start and there are few at the >200W power level.
 
You can't buy off the shelf power transformers and output transformers for this sort of power.

Maybe not rated for 500 watts but 400 watt OPT's are available off the shelf from Plitron. The PAT-4141-00. It weighs 23 pounds and costs $408 EACH!

I am sure that a suitable power transformer or combination of transformers can be found too.

I plan to build a big amp. I have no set power goals other than 200 to 500 WPC. The lower limit is set by the fact that I have already squeezed 200 WPC out of Petes red board, and the upper limit is set by what I can get out of the wall outlet multiplied by a realistic efficiency number.

An amp of this size has been discussed on this forum for over two years and to date I don't know of anyone who has built one. There was a thread where a member disclosed a source of 400 watt Plitron OPT's for $134 each, of course I bought a pair, and so did a few other members.

http://www.diyaudio.com/forums/tubes-valves/100852-eight-807s-push-pull.html?highlight=plitron

This amp was most recently discussed here:

http://www.diyaudio.com/forums/tubes-valves/162950-monstrous-1kw-amp.html

I have seen the red board crank out a stable 150 WPC through the Plitrons with the 8 ohm load on the 4 ohm tap to reflect a 2500 ohm load. Build a big power supply, and use two red boards, one for each channel, with the two channels on each board paralleled through the Plitron set for its rated 1250 ohms. This will make 300 WPC. Of course this is the easy way out, and I only have one red board, but I might try it since I have everything.
 
Cannibalize an old AM ham radio transmitter. You could use the modulator; a 1000W rig would have a 500W modulator.

Only problem, the secondary wouldn't be voice coil friendly. But it could be rewound.

Use a pair of 250TH tubes. Maybe 2500 or 3000V on the plates.
 
I find output transformers are a limiting factor- in cost, voltage rating or weight! I think the size/weight of the transformer limits winding machines.

If you run a pair of "big" transmitting tubes, the plate voltage is high (1-2kV) and the output transformer can't take it unless you have special HV windings. That's custom iron and surely expensive. Also the big bottles use forced air cooling (i.e 4CX250's).

Otherwise, you use a bunch of medium-voltage output tubes (i.e. six to eight 6550's at 550V) with a Hammond 1650W or PAT-4141. They have "low" voltage ratings intended for 600V or less plate voltages.

The Hammond 1650W is rated 280W at 1900ohms primary, weight is 28 lbs, about $315.

The Plitron PAT-4141 is rated 400W at 1250ohms primary, weight is 23.5 lbs, about $410.
 
Toddbailey......what is the lowest frequency operation at full power you are anticipating ? I'm strongly inclined to keep design to commercial tubes that are currently manufactured. 6550,KT88,KT90 and so on.
Example:-An E&I 200W o/p tranny set at 15Hz will weigh 25Lbs. (designing for 40Hz can expect half the iron weight) and the mains probably around 35Lbs or more. With the chassis (reinforced), Can you lift this heap or need a fork truck ?

Parallelling same make o/p trannies is an idea but not a space saver, but I prefer a single lump.


richy
 
The Hammond 1650W is rated 280W at 1900ohms primary, weight is 28 lbs, about $315.

The Plitron PAT-4141 is rated 400W at 1250ohms primary, weight is 23.5 lbs, about $410.

Something doesn't quite add up here. When it comes to cars the saying goes "there's no replacement for displacement". Can one of you native English speakers make a rhyme out of "there's no substitute for iron" ? :)
 
Toddbailey......what is the lowest frequency operation at full power you are anticipating ? I'm strongly inclined to keep design to commercial tubes that are currently manufactured. 6550,KT88,KT90 and so on.

Example:-An E&I 200W o/p tranny set at 15Hz will weigh 25Lbs. (designing for 40Hz can expect half the iron weight) and the mains probably around 35Lbs or more. With the chassis (reinforced), Can you lift this heap or need a fork truck ?

Parallelling same make o/p trannies is an idea but not a space saver, but I prefer a single lump.


richy


I am looking to replace several transistor amps (5) (home theater) and a McIntosh tube amp (audio only) with higher power designs

some movies like Terminator present problems. After reading the above posts any tube amp much larger than 200 wpc might be impractical. perhaps I could use the mono block design using a single or a pair of 813 tubes per channel
 
Something doesn't quite add up here. When it comes to cars the saying goes "there's no replacement for displacement". Can one of you native English speakers make a rhyme out of "there's no substitute for iron" ? :)

I believe in Einstein's equation E=mc^2 as applied to tube gear:
More power, more mass. More iron. It doesn't rhyme.

I have some Hammond 1650N's rated 60W and find they are conservatively rated, good to 90W.
 
Something doesn't quite add up here. When it comes to cars the saying goes "there's no replacement for displacement". Can one of you native English speakers make a rhyme out of "there's no substitute for iron" ?

When all automobile engines were of similar design and all had 2 valves per cylinder, the saying was true. Today it is hard to judge an engines output potential by displacement alone.

When all transformers were of EI construction, mass was a suitable means to judge the power capabilities of a transformer. In this case we are comparing a 2 valve cast iron engine, the EI constructed Hammond, to a 4 valve VVT aluminum headed high RPM screamer, the toroidal Plitron. Since a toroid makes more efficient use of the magnetic flux, it can have less iron (but about the same copper) for a given power output.

I purchased a pair of surplus Plitron OPT's that were intended for a bass guitar amp (discussed in the 8 X 807 thread). The label on the transformer says 400 watts at 20 Hz. I have not tested them at this power level yet, but I have been to 200 watts at 20 Hz. No saturation was seen. You do however need to carefully balance the DC current between the two sides to avoid saturation.

I am building a big P-P amp for two reasons. One is just because I can, and the other is that over the years I have already collected all the expensive parts without spending a fortune. I plan to build this amp for $500 to $1K including the chassis. Much of that has already been spent since I have the tubes and transformers. Yes it will be heavy, but I will deal with it. Do I need 200 to 500 WPC? NO. Will I use 200 to 500 WPC, Not unless I want to set my speakers on fire!

If I wanted to set up a big HT system (no room in my tiny house) I would use a big fat SS amp for the sub. Something like the 950 watt Crown that I recently gave away (half of a CE2000, the other channel is blown), or a class D amp. For the 4 main channels I would use a P-P tube amp of about 50 WPC. 200 watts of tube amp power could be run a lot closer to clipping without sounding bad and be as loud as 1000 watts of SS power set to avoid clipping on loud peaks.

Something like that would be a realistic build and wouldn't heat your whole house.
 
I am looking to replace several transistor amps (5) (home theater) and a McIntosh tube amp (audio only) with higher power designs

some movies like Terminator present problems. After reading the above posts any tube amp much larger than 200 wpc might be impractical. perhaps I could use the mono block design using a single or a pair of 813 tubes per channel


100 watts per channel can be done with pairs of 6550s or KT88s or any of a bunch of the bigger sweep tubes e.g. EL509, or transmitter tubes as small as the 6146B, all under 800V B+. You could build 2 channel 100 WPC amps with three $100 transformers each. And you could lift them. I think that's a sweet spot for practicality and I would bet will be overkill for everything but the low end. There maybe some monster amp but maybe it doesn't need to be a tube amp.
 
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