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#1
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Lafayette 550 with 807's
The best tube power amp I have ever owned was a Lafayette 550. Others I
have owned were Mcintosh, Harmon Kardon, Heathkit, Eico, Pilot, Magnavox, Eric and Dynaco. Never any new stuff. The 550 used 7027 outputs that are now near unobtainable. Well its just a great 6L6GC with a different basing, but is not a 807 as well except for higher max plate and lower max screen? The 550 circuit is very similar to the HK Citation 2 and by the same designer. I have a pair of 550 output tranys so how about using 807's or 1625's instead? Plus they look bitchin. What do you guys think? Eric |
#2
Posted to rec.audio.tubes
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Lafayette 550 with 807's
"The best tube power amp I have ever owned was a Lafayette 550. Others I
have owned were Mcintosh, Harmon Kardon, Heathkit, Eico, Pilot, Magnavox, Eric and Dynaco. Never any new stuff. The 550 used 7027 outputs that are now near unobtainable. Well its just a great 6L6GC with a different basing, but is not a 807 as well except for higher max plate and lower max screen? The 550 circuit is very similar to the HK Citation 2 and by the same designer. I have a pair of 550 output tranys so how about using 807's or 1625's instead? Plus they look bitchin. What do you guys think? Eric Newsgroups: rec.audio.tubes From: flipper Date: Thu, 31 Dec 2009 10:39:31 -0600 Local: Thurs, Dec 31 2009 10:39 am Subject: Lafayette 550 with 807's On Thu, 31 Dec 2009 00:39:22 -0700, sortech wrote: The best tube power amp I have ever owned was a Lafayette 550. Others I have owned were Mcintosh, Harmon Kardon, Heathkit, Eico, Pilot, Magnavox, Eric and Dynaco. Never any new stuff. The 550 used 7027 outputs that are now near unobtainable. JJ/Tesla makes them at only a few bucks different than their 6L6GC Sovtek also makes one. Well its just a great 6L6GC with a different basing, Higher plate V, screen V and plate power on the 7027 but there are those who claim a 6L6GC will sub. I tend to suspect that, while a 6L6GC may appear to initially work, it might not last as long... but I have no basis other than the data sheets. but is not a 807 as well except for higher max plate and lower max screen? 807 is a 6L6 with higher plate V, but it's not a GC. The 550 circuit is very similar to the HK Citation 2 and by the same designer. I have a pair of 550 output tranys so how about using 807's or 1625's instead? Plus they look bitchin. What do you guys think? I think you may well burn 'em up if trying to run like a 7027 but, who knows? One of the interesting things about tubes is they sometimes used parts from the 'bigger' model in the older types to conserve parts stock so you might end up with 807s sporting GC plates, depending on who and when they were made. There's a fellah selling 6BG6s on just that basis. Claims his tubes were made from GC parts. http://www.vacuumtubes.com/6BG6.html Maybe the Philips/ECG 807 was made the same way. I don't think I'd want to design one around that, though. Note: It is sometimes confusing to compare data sheets because they do not all use the same rating standard. For example, my 807 data sheets are Absolute Maximum while my 6BG6s are Design Center (6GB6G) and Design Maximum (6GB6GA) so there's a spread of 20-25 plate Watts for 'the same thing'. It's further complicated by ratings for 'different uses' often being different because ratings are determined by a mysterious 'life expectancy' analysis." I prefer new transformers, for a lot of reasons. Lafayette did not spend a whole lot of money on their products. My guess is that if you have a pair of these transformers they would be of more value to a collector needing them for a repair than better new transformers would cost. An 807 or 1625 is NOT the same thing as a later 6L6 variant or 7027. You may or may not get away with substituting them in typical audio output stages. The screen voltage rating may be exceeded with ultralinear connection when run from a primary tap, but otherwise should be respected. That means under 300 volts on the screens, which means a separate screen supply if the plate voltage is near typical values. What makes purpose designed audio output types like 6550, 6L6GC/5881, 7027 and EL34 different from transmitting and sweep tubes is that the screen grid is designed to tolerate being operated at near plate voltage, in the case of the 6V6 actually above plate voltage, which is not the case with the others. Screen grids are really supposed to operate at much lower voltages but in audio this means complicated design. There is actually a good reason why few commercially built audio amps used transmitting tubes but it can be done if you are willing to pay the piper in increaed complexity. IMO the 807 and similar tubes are fine audio tubes but only when run triode mode at conservative ratings or with a transformer with a screen grid separate winding. |
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