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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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In Reply to: RE: Did I see Gold Lion now has a EL84 posted by Eli Duttman on October 11, 2016 at 10:11:52:
". . . the O/P tubes are worked VERY hard."
When I rebuilt one of my S-5000s a couple of months back I was rather surprised that, according to the schematic, the 7189s were run at a plate dissipation of only 8.59 watts. Since both the 7189 and the EL84 have a dissipation rating of 12 watts, that doesn't seem particularly abusive.
In contrast, I just finished rebuilding a Fisher SA-16 amp that was pulled from a console. According to the schematic, and from my actual measurements, that amp was running the output tubes at a dissipation of 13.34 watts. I should note that it had two dead (white getter) output tubes that had to be removed in pieces! While I made some adjustments to bring it down under 12w, it's still running them harder than my S-5000 despite the fact that the voltages are lower.
It makes me wonder if the physical design of the amp makes more of a contribution to the amp's reputation (which is constantly repeated on here) for being tough on tubes. I don't think I've ever seen (not saying there aren't any) another design where four output tubes and a rectifier tube were placed in such close proximity. On top of that, they added a heat shield whose main purpose seems to be to keep the cabinet cooler to the touch, yet it probably serves to concentrate even more heat around the tubes.
One result of this is that the wiring around the output tubes is often fairly well toasted. If you take a close look at some of the pics of rebuilt S-5000s that have been posted here, you can see how some of the wiring in that area looks somewhat charred. While none of the wiring on mine seemed to be at the point of shorting out, I was concerned about how well it would fare in the future so I rewired that area with mil-spec teflon wire.
The S-5000 may be a tough environment for output tubes but I question how much the circuit's operating points contribute to this.
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Follow Ups
- ". . . the O/P tubes are worked VERY hard." - FlaCharlie 10:17:40 10/12/16 (5)
- RE: ". . . the O/P tubes are worked VERY hard." - Eli Duttman 12:53:54 10/13/16 (4)
- RE: ". . . the O/P tubes are worked VERY hard." - FlaCharlie 19:25:15 10/13/16 (3)
- RE: ". . . the O/P tubes are worked VERY hard." - Eli Duttman 13:19:02 10/14/16 (2)
- RE: ". . . the O/P tubes are worked VERY hard." - FlaCharlie 07:56:34 10/15/16 (1)
- Is My Logic Flawed? Please Explain . . . - FlaCharlie 19:06:27 10/18/16 (0)
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