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Old 21st May 2010, 04:49 PM   #41
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Quote:
Originally Posted by Allen Wright View Post
Something no one has mentioned, or at least given the weighting it deserves: HEAT.

Tube amps that you would want to listen to are AT BEST 50% efficient, so consider 2kW into the room anytime they are all running.

So amps of the number and power requested by the OP will COOK him and all his room partners. In mid winter this may be welcome if you live in the Arctic, but come summer and the air con bill will be equal to the power bill for the amps = serious.

Or it will be HOT and very likely VERY uncomfortable.

Regards, Allen
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.
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Old 21st May 2010, 08:44 PM   #42
ChrisA is offline ChrisA  United States
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Originally Posted by toddbailey View Post
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
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."
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Old 21st May 2010, 08:53 PM   #43
ChrisA is offline ChrisA  United States
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Originally Posted by atmasphere View Post
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.

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.
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Old 21st May 2010, 09:14 PM   #44
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I'd ask "Why" but I assume the answer is "Because I can, and I have a pile of spare cash."
In my case it is because I can, don't have even a small pile of spare cash, but have collected all of the hard to get parts over the last few years, including the 400 watt OPT's.
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Old 21st May 2010, 11:29 PM   #45
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The technical term for that is "chimney"...
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Old 21st May 2010, 11:30 PM   #46
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Oh, don't run any DC offset on those Pliotrons - read the fine print.

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Old 22nd May 2010, 12:17 AM   #47
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Originally Posted by atmasphere View Post
...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.
Good idea if you own the house, but apartment dwellers will have a problem I think...

Regards, Allen
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Old 22nd May 2010, 12:28 AM   #48
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by Allen Wright View Post
Good idea if you own the house, but apartment dwellers will have a problem I think...

Regards, Allen
Some home owners too..
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Old 22nd May 2010, 12:57 AM   #49
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Oh, don't run any DC offset on those Pliotrons - read the fine print.
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?

Quote:
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.
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.
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Old 28th June 2010, 03:13 AM   #50
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I collected a bunch of big sweep tubes at the Dayton hamfest so soon I plan to see how much power the red board will make when wired as a mono block. Should do close to 400 watts.......MAYBE THIS WEEKEND.
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:

Posted new P-P power amp design
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