On Thu, 15 Jul 2010 18:00:34 -0400, "MarkS"
wrote:
"notme" wrote in message
.. .
hello all
would welcome advice on a scott 299c bought with 4 6l6 valves, andd i
would like to fit the intended 7591 valves, i have no manual for this
amplifier and i note JJ 7591 S (with base) and 7591 7591A Electro
Harmonix (without base). can any of these valves do and is there any
difference? the amplifier to my ear has always sounded slightly
distorted to me and i hope by fitting the right valves may improve
things. i have just basic technical knowledge although i am a retired
wireman so handy with a weller
Here is a link to a pdf of the original schematic.
http://hhscott.com/pdf/299C.pdf
The pin out of a 6L6 is different than a 7591A so unless adapters are being
used between the sockets and the 6L6's, the sockets will have to be rewired
to the original connections. A 6L6 needs a higher bias voltage than the
7591A so either the bias supply was modified for higher voltage or it is
possible that cathode bias resistors were installed between the tube cathode
and ground to add self bias to the original fixed bias. The original has the
cathodes tied directly to ground. The JJ 7591A's are closer to the original
7591A diameter than the EH tubes. I do not have any experience with these
new 7591A's as far as reliability goes.
Start by studying the schematic and compare it to your amps current wiring.
Good Luck,
Mark
sorry Mark
i posted before i refreshed so i have just seen your post. yes looking
at the socket its clear that they have been modded, but i will
reinstate back to as per the wiring diag when i am satisfied which
7591 to buy, i note your suggestion 7591a being nearer to eh tubes and
will probably act on that info
thanks
bernard