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#1
Posted to rec.audio.tubes
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can any one with knowledge of Scott 299c help please? TIA
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 |
#2
Posted to rec.audio.tubes
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can any one with knowledge of Scott 299c help please? TIA
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. |
#3
Posted to rec.audio.tubes
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can any one with knowledge of Scott 299c help please? TIA
"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 |
#4
Posted to rec.audio.tubes
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can any one with knowledge of Scott 299c help please? TIA
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. |
#5
Posted to rec.audio.tubes
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can any one with knowledge of Scott 299c help please? TIA
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 |
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