There is a way to deal with the heat, without air conditioning, if you have a dedicated listening room: set up a vent in the ceiling above the amplifier(s) so that the heat they make is vented out of the room. I know someone who has a very high power set of amps in Guatemala City, and without air conditioning his room stays comfortable all year, day and night, even if the amps are on all day.
What speakers will this amp drive? Is it single driver speakers? If not you'd be best off building a four channel amp. The problem is finding an output transformer that can do 500W and have both good bass and good highs as well. If you split the left and righ channels into left treble and left bass same for right side. Then you could use off the shelf OPTs.
I'd ask "Why" but I assume the answer is "Because I can, and I have a pile of spare cash."
Yes, one does not need to cool the entire room, only to keep the air around the amp below some safe limit. Forced air cooling with the option to use vents through an exterior wall would work fine.
Good idea if you own the house, but apartment dwellers will have a problem I think...
Regards, Allen
I have already seen what some offset can do. On the other hand setting the balance is rather easy, just crank a 20 Hz sine wave through the amp at about 100 watts and tune for lowest distortion. That works on just about any P-P amp, but the effect is most obvious with the Plitrons. I have also seen some unusual effects with tubes of greatly mismatched Gm. You can balance the amp at one power level, but it is off at another power level. It will be interesting to see what happens when I start paralleling output tubes.
The story on the OPT's that I have is that they were an unpotted version of the PAT-4141. Plitron made a batch for Marshall to use in bass guitar amps. They didn't work out (imbalance problems?) so they wound up on Plitrons surplus page. I had them running for about two weeks at 100WPC and they sound really nice, but why use a 400 watt transformer for a 100 watt amp?
I toyed with the idea of heat extraction via a clothes dryer vent when I was infatuated with building a 200 WPC SE amp using 833A's. The lack of a suitable OPT killed that project but the IR radiation given off by a glowing anode at 500 watts of dissipation will make you sweat even with both AC units running!
I have central air in the house, and I installed a "booster" window unit in my work room. With both units cranked the temp is livable with my 845SE amp, and the lights, computer and other usual stuff on. That amp dissipates about 500 watts at normal listening volume. That should be the maximum dissipation level for whatever I build at my normal listening level. The easiest way to get there is likely a system where pairs of output tubes can be shut down for lower powered operation.
I had the red board, and the sweep tubes, but no time. So here a month later I plugged the first pair into the red board and cranked up one channel. 250 watts for one channel meets the criteria discussed here. This was using a relatively stock board, running on external power supplies. When time permits I plan to hook the second channel to make a 500 watt amp.
See post # 425 in this thread:
http://www.diyaudio.com/forums/tubes-valves/151206-posted-new-p-p-power-amp-design.html
I built a prototype 100 watt amp using 4 off KT88 in Ultralinear. I tried it with both a Hammond 1650T Iron Core Output Tranny and a Plitron PAT-4006 Torroidal Output Tranny (basically the same Raa and power rating).
The sound was remarkably different. What many regard as "That Tube Amplifier" sound is the increasing second harmonic distortion at low frequencies as the rp of the tubes comes close to the impedance presented by the output trannies primary inductance. Now the Hammond had a primary inductance of around 60H and with it the amp had that "valve amplifier sound". The Plitron had a primary inductance of 560H and with that in the amp it did NOT have that "valve amp" sound - bass went lower and was perhaps tighter and better controlled but was subjectively "weaker", due no doubt to the absence of that low frequency 2nd harmonic distortion.
You actually see the result of this in some of the newer guitar amps now on the market. Those that incorporate a toroidal output tranny often have an additional preamp gain stage to allow some additional build up of harmonic content to offset that lost when using the toroidal output tranny in the power amp section.
Cheers,
Ian
The sound was remarkably different. What many regard as "That Tube Amplifier" sound is the increasing second harmonic distortion at low frequencies as the rp of the tubes comes close to the impedance presented by the output trannies primary inductance. Now the Hammond had a primary inductance of around 60H and with it the amp had that "valve amplifier sound". The Plitron had a primary inductance of 560H and with that in the amp it did NOT have that "valve amp" sound - bass went lower and was perhaps tighter and better controlled but was subjectively "weaker", due no doubt to the absence of that low frequency 2nd harmonic distortion.
You actually see the result of this in some of the newer guitar amps now on the market. Those that incorporate a toroidal output tranny often have an additional preamp gain stage to allow some additional build up of harmonic content to offset that lost when using the toroidal output tranny in the power amp section.
Cheers,
Ian
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One way to get around the issue of one big output transformer per channel is to think about doing what the solid state PA guys do when they want a lot of power, go to a bridged output. A stereo power amp in bridged mode for mono high power. Two smaller output transformer in bridged mode. You can bridge a tube amp just like a solid state amp for higher power with smaller sized output transformers compared to one big output transformer. Just something to think about.
I posted some THD test results in the red board thread at power levels up to 250 watts.
http://www.diyaudio.com/forums/tubes-valves/151206-posted-new-p-p-power-amp-design.html
What is needed is some enterprising company to design and market tube amp kits that provide the hundred plus watts power most of use desire. And at a reasonable price.
Ideally, this company would provide, among others parts lists, specialty parts, circuit boards, custom chassis & schematics etc.
There are a few such companies around today, but cost per watt is excessive.
Perhaps a amp using 4 or more kt-88 or equiv. per channel might be a good place to start.
Ideally, this company would provide, among others parts lists, specialty parts, circuit boards, custom chassis & schematics etc.
There are a few such companies around today, but cost per watt is excessive.
Perhaps a amp using 4 or more kt-88 or equiv. per channel might be a good place to start.
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how 'bout this : )
Dynaco A440's running either 6 EL34's, or 2 813's ?
Analog Audio Amplifier Design
I scored a single dual - chassis mono amp a year ago, and it was not finished, but I'm pretty sure it was based on this schematic . . . it's got a pair of 813's for output tubes, a UTC LS-7 interstage transformer, and unknown driver tubes (weren't any when I got it - just bare sockets)
the power supply is choke input, dual 866's and a UTC S-47 power transformer
I have yet to do anything with it, but if you scored a couple A440's, you could probably get 200W . . . .
Dynaco A440's running either 6 EL34's, or 2 813's ?
Analog Audio Amplifier Design
I scored a single dual - chassis mono amp a year ago, and it was not finished, but I'm pretty sure it was based on this schematic . . . it's got a pair of 813's for output tubes, a UTC LS-7 interstage transformer, and unknown driver tubes (weren't any when I got it - just bare sockets)
the power supply is choke input, dual 866's and a UTC S-47 power transformer
I have yet to do anything with it, but if you scored a couple A440's, you could probably get 200W . . . .
The "reasonable price" part is not going to happen. The problem is the 200W transformers are going to cost big $$$. And then you need to mount them on a chassis that can hold 50 pounds of iron without flexing. The iron and mechanical parts will never be cheap. Tubes at about $25 each are not bad and the rest s nickel and dime stuff. Transformers alone are going to set you back at least $750, Tube cost about half that. A kit supplier is NOT going to be able to get those costs down
As for a PCB. Mostly with six or eight big tubes per channel the wiring in the power section is going to have to be point to point. So what's left for a PCB? a gain stage and a phase splitter? There are already many Dynaco PCBs that would work.
How many people really want a $1200+ "kit" If you need that kind of power SS is the way to go unless it is just for show or bragging rights.
I found Hammond has 280 transformers at about 250 ea. they also have smaller units available next size down is a 120 watt size.
But the 200 + watt monster does weight 30 pounds. So probably you'd have to build 2 amps just so they could be moved.
Or utilize a relay rack, on wheels no less.
Bottleheads has a few kits but they are way out of my price range and don't really produce any meaningful power.
SS amps produce the raw power but none I have listened too sound all that great, If they did, why would I have a 50 year old amp in the listening room?
I may downsize this project once again, I guess a 120 watt design is the more practical route to take
As for a chassis, maybe I can make use of that old dinosaur HP server after all,it's weigh is 120 pounds and is 1ft high, 17 wide and 24 deep...
But the 200 + watt monster does weight 30 pounds. So probably you'd have to build 2 amps just so they could be moved.
Or utilize a relay rack, on wheels no less.
Bottleheads has a few kits but they are way out of my price range and don't really produce any meaningful power.
SS amps produce the raw power but none I have listened too sound all that great, If they did, why would I have a 50 year old amp in the listening room?
I may downsize this project once again, I guess a 120 watt design is the more practical route to take
As for a chassis, maybe I can make use of that old dinosaur HP server after all,it's weigh is 120 pounds and is 1ft high, 17 wide and 24 deep...
don't forget the monster McIntosh MC-3500 - 350Ws of tube power
Loose Random Stuff | Uneeda Audio
honestly, for driving inefficient speakers, I've go solid state. My Threshold S/500 does a great job running my Magnepans.
Loose Random Stuff | Uneeda Audio
honestly, for driving inefficient speakers, I've go solid state. My Threshold S/500 does a great job running my Magnepans.
I base my 150+150W designs around 19" rack dimensions; a stereo with 8 o/p tubes with the 4 drivers and other small ones it's tight. Ventilation becomes an issue as does the mains transformer, eg, for 8 x KT88 fixed bias one has got to recon on a power transformer capable of supplying a min of 700W and more if capacitive input filtering is used. I get around this by using power factor control with a slightly smaller mains transformer. The 8x power tube heaters require a conservative 20A winding if KT90's are used.
A top flight UL output transformer in the pic capable of 20Hz-50Khz at 150W will set one back $500 and the mains at an equally painful price.
The weight of the entire amp in pic is around 75Lbs and as others mentioned the chassis fabricated to accept the weight.
How much would it cost to make this quality HiFi performing amp; bits + mytime technology + skinny profit ? For a start, $1000 for the iron. $500 for the tubes, assuming chassis bits ready, for an expert roughly 3wks finish assemble. labor costs, one ain't short asking between $7.5K and $10K depending on ones location.
One pays for frequency range. For MI with 40Hz cutoff, life and technology become far more amenable. Your choice.
richy
A top flight UL output transformer in the pic capable of 20Hz-50Khz at 150W will set one back $500 and the mains at an equally painful price.
The weight of the entire amp in pic is around 75Lbs and as others mentioned the chassis fabricated to accept the weight.
How much would it cost to make this quality HiFi performing amp; bits + mytime technology + skinny profit ? For a start, $1000 for the iron. $500 for the tubes, assuming chassis bits ready, for an expert roughly 3wks finish assemble. labor costs, one ain't short asking between $7.5K and $10K depending on ones location.
One pays for frequency range. For MI with 40Hz cutoff, life and technology become far more amenable. Your choice.
richy
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