Only 1 changed resistor inside in 40 years, pretty good for twice weekly use over most of that time. Heaters glow but HT and bias supply stays up and no extra current draw coming out of standby. The 2.2K 7W W/W dropper for the minor HTs gone o/c. First set went fine, switched to standby for break and then nothing there for the second set. Is that resistor most stressed in standby? No obvious overheating of the R or the whale hide or whatever "circuit board" material. Assuming no other problem , it just failed from old age/corrossion but replace with same rating or go up to 11W? No rubber insulation found , any health and safety considerations other than the usual modern considerations? 2 issues with the Bulgin plug+socket mounted on the cab but thats just a UK thing. I'll do the usual remove the red voltage selctor knob on the rear and secure inside and blank off the shaft of the switch, as too easy to drunkenly turn that knob to "repair" a fault situation in UK 240V land.
Fender Bassman Ten, 1975
Oct 15, 2015
1 Replies
Bad mains earth bond-point. Decided to autopsy the Rockwood , presumably original, 2.2K 7W dropper, the previously replaced one is elsewhere 1/2W . Stopped going in further when it looked as though asbestos was part of the construction. I'd not thought how fine the wire must be for 2.2K. Looks as though the asbestos wraps around the core , for thermal expansion give, allowing isolation of the turns at the same time, then covered in fire-cement set in a moulded ceramic body. As brown colour at one end I'll assume it was rust and failure was corrossion, the resistance wire looked fine , what I could see of it but making contact with it meant it locally broke.
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