can any one with knowledge of Scott 299c help please? TIA

[notme]

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

[Kruse]

On Jul 13, 12:01*pm, notme > wrote:
> 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

Are you positive that the output transformers are original?
Obviously, you need to get a manual that has the wiring diagram.
Also, check to make sure that the new tubes do not have a larger
diameter than the original tubes, as the 7591s sit real close to the
output transformers on a 299C with factory output transformers.

[MarkS]

"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

[notme]

On Thu, 15 Jul 2010 04:15:38 -0700 (PDT), Kruse >
wrote:

>On Jul 13, 12:01*pm, notme > wrote:
>> 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
>
>Are you positive that the output transformers are original?
>Obviously, you need to get a manual that has the wiring diagram.
>Also, check to make sure that the new tubes do not have a larger
>diameter than the original tubes, as the 7591s sit real close to the
>output transformers on a 299C with factory output transformers.

thanks for your response
as you have hi lighted, the closeness of the tube to the transformer.
thats another reason why i want to ghange back to 7591, the 6l6 valves
that ive got in currently are actually touching the transformer which
cannot be good for them with all the extra heat transferred,( i have a
leak amplifier with el35 valves and those are not nearly as fat as 6l6
for that matter if i plug in a el35 into the socket there is a gap of
4mm clearance). my real question again is, in that respect is the jj
7591 fatter than the electro harmonics 7591, is there a difference of
quality between them, does the closeness of the valves eventually
cause damage to the transformers? i note from the picture that the
latter has not appear to have a bakelight base as the former, and is
any of them as fat as the rca 6l6?
i feel certain i have the original output trannys as per factory, i
also can easily obtain a schematic from various sites, i do note i
modification (maybe to do with the fitted 6l6) 330k resistors soldered
to the wipers of the dc adjusters.

[notme]

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