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Old 16th July 2011, 01:11 PM   #1
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Default NOS Svetlana 6550s work fine - wish I liked'm better

Turns out that while I'm not too shmart, I still can build. It was a bad tube. Thanks so much to RKnize who gave me his time.

Only place I can find to sell a single E-H 6CA7, my longtime fav, is Triode and they want almost the price of a pair everywhere else. No quarrel with Triode, I just hate to have another threesome!

Right now I have the highly touted, above-mentioned Svetlanas in and they just don't have that mid-range magic of the fat bottles. Maybe it's operating point? The 560 Ohm cathode resistor remains giving 425 vDC at pin3 and 455vDC at the output.

Do the KT-88 numbers on the "Tubes and Transformers" page apply to 6550? I have or can create other value 5W+ resistors.
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Old 16th July 2011, 02:13 PM   #2
rknize is offline rknize  United States
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6550 and KT-88 are pretty close. The KT-88 spec can handle more dissipation, but most modern 6550s are KT88s in a different bottle anyway. The SED (old Svetlana) are probably the only exception. I have a pair of SED 6550-C in my SSE right now and I think they sound pretty good overall. You might try running them a little hotter. I run mine at something like 390-430 ohms.
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Old 16th July 2011, 06:17 PM   #3
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Default One year later...I love these things!!!

It must be the new speakers, cause I'm not a big believer in break-in making serious changes, but these pre-Sovtek Svetlana 6550s are Fabulous now! Much more bass weight, sonority in the brass, realism in voices, air, tone, texture.....and headroom, don't forget headroom: 3 times the power of my 45 amp.

Let's hear it for Edgar Vilchur and acoustic suspension, too. I was given these 12inch Utahs with no specs but a good recommendation so I figure, 1.5 to 2.5 cubes, sealed might be good. Put it together with the new-new SB-29 Tweeter from the guys that got canned from Peerless when it got bought out. First order, 2000Hz ('cause I trusted the tweeter more than the woofer and the low 600Hz Fs let me do it).

The result is this 2.3 cu ft floorstander with kinda gaudy walnut finish, and oh boy, isn't dumb luck the best kind?
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Old 16th July 2011, 08:03 PM   #4
rknize is offline rknize  United States
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Glad to hear it. The midrange on my main speakers is rather lacking, but they seem to be easy to drive (98dB). When driving a tougher load, like my Boston Acoustics A70s (also acoustic suspension), the SSE with KT88s running hot give the most bass control. They give up detail though, especially in the midrange. I have a set of New Sensor reissue Tung-Sol 6550s and they sound just like the KT88. The SED 6550 need to be run cooler and don't have quite the bass as the KT88. But they sound better overall and are a nice compromise IMO.
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Old 17th July 2011, 02:42 PM   #5
w5jag is offline w5jag  United States
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Antique Electronic Supply advertises EH 6CA7 singles at $17.50 / tube.

Win W5JAG
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Old 17th July 2011, 05:58 PM   #6
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Many Thanks, I always forget to check there.
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