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O.K. getting ready to start. There are TWO TP-26 spots on these prints. One gratefully says bias test point near R-66. The other is on the layout one one side of R-55. That's confusing, but I will go with the one at the edge of the board, as i was instructed to do where it does say bias test point. I have read that these amps are biased cold from the factory, but 30 ma per side sounds about right to me, so I'll go for the 60 ma (m volt)measurement at that spot. I wish I could enlarge these prints, they're so doggopne small. The OTHER TP-26 near R-55 wants +_42.5 VDC. I'll ignore that, but I've never seen prints with the same TP designation for two different parts of the circuit. Here we go!...Bob I will try using the effects loop after that to see if it works that way, and report back...
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That's an error on the drawing. The bias test point is at R66.Originally posted by picknconk View PostComment
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Never heard about stranded wire being more prone to oscillation than solid wire before, but I learn at least something or often many things every day so I'm open to the possibility (though a little skeptical I must admit).
All of the stock ribbon cable conductors I have seen on those amps have been stranded but also tinned along their entire length, making them appear solid until one breaks and you get a good look at the scraggly severed ends. I have seen this type ribbon cable used in many pieces of gear from CD players to mixing consoles and pro audio amplifiers. In fact a lot of those pieces of gear use SIP sockets into which the tinned-conductor ribbon cables directly insert (Hmmm...maybe an idea for a mod on these amps).
The wires I used in that aforementioned experiment were stranded FWIW. The oscillation issue seemed to have to do with the spatial relationship of the wires to each other.
A plenty smart & experienced tech I used to work with espoused immobilizing the ribbon cables where they meet the boards with hot glue or the like before commencing board R&R on these amps.Comment
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HEY EVERYBODY!...Is there any good reason why I shouldn't replace those dreadful ribbon cables with individual wire? I hate them, they're too rigid, and I want to shorten the lead length. Their stiffness and mashed down configuration lend themselves to problems....any responses?I wonder if it's a mistake to install the Mod. kit before I find the problem, as it might replace the faulty part. My instincts tell me to fix it first. I also am inclined to replace the supplied upgrade Electrolytics just because.Oh lord...How about removing the extension jack from the circuit, I don't use them..?
PLEASE PLEASE PLEASE don;t start ripping stuff out and changing in until you get the amp fixed. The one good reason is that it adds oh so many more opportunities to obscure the solution to your problem. You could have a fault in a ribbon causing the symtpom, but it is not BECASUE it is a ribbon, it is because of a fault. 10,000 of these work fine with the ribbons, and this one did earlier in its life. The solution to this problem will not be in replacing the ribbons.
The electroncs don;t care a whit about the stiffness, and that little S-bend won't upset the works either. The ribbon wires are all parallel in layout and evenly - predictably - spaced. Loose wires - and I'd just wager, anyone replacing the nice neat ribbon with wires would tie them together with a tie wrap for "neatness" - can lay any which way, and frankly wil be more likely to cause grief than ribbons.
If you pull the board in and out a lot, yes, the flexing will do the ribbons no favors, but most amps don;t live that way.
Once the amp is sorted out, THEN is the time to entertain thoughts of swapping stuff out.Education is what you're left with after you have forgotten what you have learned.Comment
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O.K., I did assume they were stranded from the feel of the assembly, although tinning changes things a tiny bit towards my argument. Could be I'm merely the product of being taught by old radio men. A non existent breed today. I'll leave things be, but sorta like the idea of ruggedizing the ribbon terminations. It's side chatter for my problem. I still don't know much about these low voltage power supplies that I guess are the chips I'm seeing. I'm following TP instructions at this point as I've already mentioned the whole Op amp, JFET thing is from Mars to me.. Letcha know...Bob
ENZO...I know not to bunch signal wire together, they would be as the ribbon lays, and I never , ever used cable ties, Avionics always uses waxed cotton flat braided tie cord. Plastic shrinks, gets brittle, cuts into insulation, I never go near those things. Thanks for your cautionary advice..I'll leave those be, after validating all joints and maybe continuity...Comment
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You will hear from me eventually, illness in family. I DID however have the prints enlarged at Staples to 24"x36"!! NOW I can see what I'm looking at. Just black out all the brand name and I.D. stuff and they'll do it. Mucho better. More soon.Comment
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It's so hard to know what caused the change in output. In checking the amp, it seems every wire in it was hanging on by one filament, and came off just by touching it. I'm replacing all these awful quality wires with better, and installing buss lead posts with wrap around wire connections and goop to hold it in place. I never will know what the root cause was, unless after re assembling it, it's still there. The grey wire to the output jack, every green wire running anywhere, all just let go with any movement. The ribbon wires, are not, by the way, tinned all the way through, just tiny stranded copper with tinned ends, most of those about to let go. Lots of bad joints. Sort of a good design with horrible construction. More to follow. A couple of ribbon wire ends were touching, I don't know how it worked with that being the case. Just amazing...Comment
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