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I have a Pilot SA260 amp that i've stripped down to the chassis and was going to start to re-assemble.
Part of the teardown involved new wires to the power transformers since the one that were on it were very crumbled. I attached the wires as they had been, and now it seems something is amiss: When I connect the input wires to my variac and apply even a small amount of voltage, it blows the fuse on the variac (this has NEVER happened with this variac before)
The OPTs wires look better, but still not great, so I've left those alone. This amp was working (but not too well, rectifier tubes kept dying) when I shelved it. The teardown came a couple of years after that, if that matters
Can anybody suggest troubleshooting steps, or failing that can anybody recommend a service that can look at this thing? I think finding a replacement would be close to impossible...
Follow Ups:
Kirk,
The other posters have you on a good path to resolving your issue.
Old cloth insulation IS a source of difficulty. The next time you have to deal with it, consolidate the stuff with clear nail lacquer and follow up with good heat shrink. The product is not especially flexible, but it will hold up for quite a bit of time. While it might fracture, the consolidated cloth fragments are held in place by the heat shrink.
BTW, are you planning a "stock" rebuild or are you interested in some modifications that will improve performance?
Eli D.
Eli-
Yes I'd like to improve performance but to be honest I'm not that skilled with tube circuits. I know Mike S has posted on power supply improvements via stiffening capacitance, but at my skill level I'd just be happy if the dang thing works and stops chewing through rectifier tubes.
The current production EH 5U4GB is pretty darned good and reasonably priced. If you want OS rectifiers, go with GE 5U4GBs, which are very nice and not silly expensive. Either way, Jim McShane is THE man to buy from.
Mikey has a penchant for using film caps. in the 1st filter position, when vacuum rectifiers are employed, and I agree with him. With that in mind, cement Mouser part # 75-MKP1848S65050JY5F to the underside of the chassis for that job. While the 5U4 pair could stand a larger capacitance, I don't want to overheat the precious OEM power trafo. We'll talk about the rest of the PSU, after I get a good look at some photos (top & bottom), which I request be posted.
There is extra filament current available in the power trafo that can be exploited to considerable advantage. Pilot's choice of a 12AU7 (shared between the 2 channels) for voltage amplifier duty, sucks a big wet one. :> (( The 'U7 triode is distressingly non-linear. Other than rewiring the heater connections, a 6CG7/6FQ7 drops in, without parts value changes. ;> )
Eli D.
What pictures are you requesting?
Right now I have the painted chassis, the transformers (not mounted) and a bunch of parts in a box. I can find pics of what it looked like originally if that's what you mean...
Original condition photos of both top and underside, please.
Eli D.
Bottom views: I didn't take one of the whole thing, but here are three shots that include everything. It was a mess, as you can see.
The perfboard with the diodes (which I think replaced the selenium rectifier) and some of the other work was done by a local tech years ago.
Top view: not mine, but it's the same amp:
http://i28.photobucket.com/albums/c207/whitese/pilotsa260.jpg
There are 2 "twistlok" (can) caps. whose diameters need to be measured. You will be increasing the amount of capacitance in the reservoir (C1B) and decoupling positions (C2A/C2B) using modern, clamp mounted, parts. Obviously, the clamp sizes appropriate to the chassis holes already present need to be acquired. I will "ping" Jim McShane to get his input on the subject.
Remember, C1A is being replaced by a film part that's cemented into place on the underside of the chassis.
BTW, I see only 1 diode in the bias supply. It was a nice touch on Pilot's part to full wave rectify the bias supply. Perhaps that area should be gone over too, since corners may have been cut.
Eli D.
The smaller twistlock can is 1" in diameter, the other is 1 3/8". Both are currently empty (I cut them apart and cleaned them so they could be stuffed with new caps as needed)
There is a second diode, hiding under the wire on the perfboard.
Stuffing and "gooping" is OK, but clamps are definitely more secure.
Let's see if Mr. McShane posts.
Eli D.
Why don't you send it to Gary Brown and have him test and - if required - rewind it for you? Then you know it'll be in good shape and it'll perform properly. And it'll have healthy new lead wires.
Edits: 01/15/17
In this case, maybe the Heyboer will be the fix, but I can heartily agree and I'd recommend Gary for rewinding etc., he's done a couple for me and both are splendid performers.
Jim
Heyboer actually has a replacement for that transformer and it's the same price as a rebuild and he won't have to pay shipping both ways.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Hi Mike-
I've decided to go the replacement xformer route from Heyboer as this solution is quite a bit less expensive.
Thanks for the tip!
Kirk
Good news, thanks Mike.
I'm seeing 0.8 ohms across the 120 v inputs. Open circuit between either of the 120v inputs and any other wires.
Edits: 01/15/17
Appears you did not tag the wires properly. You should measure around 5 to 10 ohms on the 120 volt winding.
Jim
I had a lot of amps measure .5 ohms on the primary and be fine. I wonder when he changed the wires,did he maybe short them against the end caps by maybe leaving leave that Mica insulator or cardboard out?
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Maybe this. I did replace the cardboard, but things were crammed in there pretty tight. I just took the end bells off and tried again, same result :(.Looks like I may need a new one. Maybe for the best, this thing looks like it's been overheated (has for as long as I remember, too)
Anyway, I've mailed both Gary and Heyboer, let's see what they come back with.
Edits: 01/15/17
I meant .5 to 1.0 ohm on primary, not 5 to 10 ohm. Follow Michaels experience and order a new Heyboer transformer.
Edits: 01/15/17
I figured that's what you meant.I make typos like that all the time.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
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