[sortech]

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

[Bret L]

"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.