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Vintage Asylum Classic gear from yesteryear; vintage audio standing the test of time. |
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Vintage Asylum Classic gear from yesteryear; vintage audio standing the test of time. |
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In Reply to: My Fisher 500B just blew up. posted by Sidewinder on April 25, 2007 at 23:47:16:
I'm sorry to hear that your B got nicked. But it does appear that the cathode fuses did their job, albeit somewhat sluggishly. I would replace all four resistors at this point. Use metal films, as they'll open the fastest, usually instantly with a loud and reassuring pop.If you already had some hum building, you might want to check the main filter caps to make sure they survived the stress. At 45+ years, all bets are now off with them.
While I've been down this road before with Jim over the Fisher grid resistor values as they relate to new construction 7591s, you can certainly bump the values down if you must. There is still an army of old Fishers chugging along just fine on 45 year old original outputs, so I don't consider Fisher's specs too aggressive for the tubes of the era.
But I would exercise some restraint in bumping the main coupling values as high as .1 uf, regardless of the outputs used.
But the reason your 7591s shorted was because of a hard jostle when running. That's a no-no with the newer production outputs, which I find less mechanically hardy than the older stuff. A 7591 has never been an easy tube to make, and I would have lingering concerns with the survivors, regardless of the tester results. For that reason, you might want to start fresh with a new quad. Outputs are still cheaper than OPTs. That, or find a set of used/test strong Westinghouses and rest easy.
Good luck!
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Follow Ups
- Re: My Fisher 500B just blew up. - sgmlaw 12:44:18 04/27/07 (0)
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