In Reply to: Suggestion Needed for Adding External Bias Point Contacts posted by jbrrp1 on June 13, 2013 at 10:28:30:
Hi, jbrrpl. Jim's tip jack suggestion is the way to go. Small test points with minimal plastic insulation. You can get them in colors other than red and black. The only problem that might be present is the metal used
for the 509 chassis. Aluminum is a lot easier to drill than steel. If as I suspect the chassis is steel you may need machine shop assistance.
You don't want to butcher the amps. As far as controls go there are made for chassis mounting pots without long shafts. I think the ones I sourced
are 1/4 inch. The measuring R are (as I recall) 10 Ohms. Get 1% R of your
choice. I recently went through this exercise with a stereo SET 2A3 amp.
Push-pull gets a little more complicated. Bias and Balance pots plus
tip jacks. You know your 509 gripe about having to invert the chassis
in order to measure current and adjust is the same gripe I have about
his first amps for Luxman - the MB-3045. I suspect this might have been
done intentionally to keep customers' fingers away from touching B+.
Drop me a line if you want to chat. Glad to help. Are you still happily
able to source the output tubes?
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Follow Ups
- RE: Suggestion Needed for Adding External Bias Point Contacts - elektron 06/14/1306:05:43 06/14/13 (0)