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Old 2nd November 2007, 04:03 AM   #11
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George -

Do you think the sound was nice enough with the 211s to be worth all the effort? I was thinking also of triode-connected 813s, but I like the safety/aesthetics aspects of the plate-capless 211s with the packaging I'm considering.
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Old 2nd November 2007, 05:18 AM   #12
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Roaming around on Fleabay, I noticed some "Eastern Audio" 10k output transformers that are purported to work with 211s among other tubes. Anybody know if these are any good?
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Old 2nd November 2007, 02:07 PM   #13
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Nice stuff, tube-lover.
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Old 2nd November 2007, 04:30 PM   #14
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A long time ago someone posted operating points of 211 and 845 tubes and found the sweet spot to be with lower plate voltages. I don't recall who it was but it could have been from Sound Practices.
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Old 2nd November 2007, 11:21 PM   #15
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hey-Hey!!!,
I'd go for as high a plate load as I could get. The plate Z of the 211 is going to vary between 4 and 6k for reasonable output. Pick your damping factor and start multiplying...
cheers,
Douglas
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Old 3rd November 2007, 12:40 AM   #16
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Quote:
Do you think the sound was nice enough with the 211s to be worth all the effort?
At the time I thought it was, and I would still build another one if I didn't already have one. The amp sounds great, but it is large (2 chassis), heavy, and pumps about 400 watts worth of heat into the air. For these reasons, it doesn't get much use now.

The whole thing got started when I got a pair of "10K ohm 211 or 845 SE" transformers from an Ebay auction. I started out building a "Poor mans Ongaku" clone (published in Sound Practices magazine), but I was unhappy with the sound. This led to the development of PowerDrive and the design of my 845SE amp. When I first put the design on my web site, my email box was bombed with all sorts of debate about what was, or wasn't an Ongaku, 211's 845's and the contamination of tube amplifiers with sand, especially a well revered design. There was all sorts of opinion about the "proper" operating point for a 211. The most popular responses were 650 volts, EXACTLY 960 volts (the Sound Practices circuit), and 1100 volts.

My amp has enough drive and bias adjustment range to allow the use of 211's or 845's. I have used both tubes in NOS and new Chinese flavors. I prefer the sound of the 845. I have also used 3 different power supply voltages. The first amp used an Audio Note power transformer and the power supply design from the magazine. I got anywhere from 890 to 950 volts depending on bias current. The second, and current power supply produces 1050 volts at the "normal" bias current of 70 mA per tube. I have run the Chinese tubes as hot as 110 mA dropping the supply to 1030 volts. To my ears this was far more dynamic than the lower supply voltage. When I was experimenting with the 833A amp, I got the idea to connect the 845 amp up to the 1500 volt 1/2 amp power supply. I removed the input cap so that I was getting about 1300 volts. The 845 positively rocked on 1300 volts at about 70 mA.

The OPT's that I have came from a supplier that turned into a first rate con artist who stole most everyones money. Too bad, because his early transformers sounded good.

I got a pair of Eastern Audio 600 ohm SE OPT's from a fellow forum poster. They work well for my intended application, and for the price that I paid for them. As with many Chinese components the specs are highly inflated. These are called "50 watt" transformers. That is probably true at 1KHz. The guy who sold them to me said that they were good for 10 watts. That seems about right. They are smaller than other 10 to 15 watt SE OPT's. I have not had the time to perform any testing on them yet. A 10K ohm transformer is a lot harder to make than a 600 ohm transformer.

As others have pointed out these tubes need a fairly high load impedance. You may get by with a lower load impedance if you choose a lower supply voltage and a higher bias current.
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Old 3rd November 2007, 03:00 AM   #17
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[QUOTE]The OPT's that I have came from a supplier that turned into a first rate con artist who stole most everyones money. Too bad, because his early transformers sounded good.

George, were these by chance "Hand Wound" transformers? If so, I also have a pair from eBay that were unused and on the shelf for a while. They may sound good (hopefully) but were made poorly. I had to shim the winding bobbin because it was a loose fit on the core. Also the air gap was very uneven so I spaced it with tape to about 5 thousandths. I think I remember you mentioning something about doing that to yours. What spacing or thickness is your gap? I may have to experiment with the gapping upon use. (someday)

Victor

edit: Why dosen't the quote function work?
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Old 3rd November 2007, 03:40 AM   #18
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If I get too frustrated with stuff for the 211, I may use this platfom instead with a pair of 6HV5As per channel. They still have the sort of retro-lightbulb look I want, and I suspect they will be able to pump out some watts if hammered hard enough.
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Old 3rd November 2007, 01:44 PM   #19
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George, were these by chance "Hand Wound" transformers?
Yes, they were. I have been using this pair as delivered for a few years. I have not had them apart. The response is posted somewhere on my web site. I got another pair of 300B transformers from him about a year later, and they were junk. I never could get them to work right. The air gap was just that, an air gap that was only set by the screws holding the end bells on, so they were "adjusted" in shipment. Most transformers use a shim of some sort. I just use several layers of Kapton tape.

I also got a pair of 60 watt P-P transformers from him. I don't know how you screw up a pair of transformers as much as these, so I will eventually take them apart to find out. I plan to reuse the cores and end bells for a 600 ohm SE transformer.

Found the transformer response curve. It is down in the middle of the page. This is the whole 845SE amp at 10 watts.

http://www.tubelab.com/845SE.htm
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Old 3rd November 2007, 02:23 PM   #20
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hey-Hey!!!,
A friend of mine also got a good pair of SE outputs from Handwound. He built a JE Labs 2A3 amp with them, and it sounds brilliant. I was quite suprised at that result given most of the stuff we've read about the Handwound thievery.
cheers,
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