Fisher 800C consistent hum. Help needed!
- Thread starter LPCOLLECT
- Start date
LPCOLLECT
New Member
thank you for identifying this capacitor leak.
I've learned a ton from you guys and from this discussion. I'd like to learn more about capacitor leakage.
are you referring to this brown bulge in the middle of these 4 connection?
LPCOLLECT
New Member
yes sir! given that the leakage from these can capacitors, I'll try to find a tech locally here in SoCal that can replace them. I definitely won't be doing this on my own.Yes. Regardless of 60Hz or 120Hz hum, the cap cans need replacing.
sorry about another follow up question here. how much should I expect (in terms of $USD) if I take this to a tech and have the two can caps replaced?
these caps don't look cheap to me.
Best to get a couple of estimates. Here's a price list to help with parts.
Labor usually is a set hourly rate.
LPCOLLECT
New Member
thank you for the speedy reply Mr.Boochie.
dang, these are quite expensive but still affordable. whatever it takes to get this 800c back in working order. I'm relying on my old Fisher RS-1052 (solid state) amp meanwhile and I miss 800c's tube sound daily.
another dumb question just for my learning. why are these can caps so large/expensive compared to polypropylene capacitors? (for example the dayton ones are like a couple bucks each at most). although I've seen some Solen or Jantzen ones go for like 30-40 bucks.
are these can caps filled with some special material perhaps? do they house many mini capacitors inside?
Electrolytic caps differ in construction versus non-polar poly coupling caps. You can buy individual electrolytic caps, but the cost will probably be the same as multisection cap cans. Plus, chassis space will become an issue unless you have the cans restuffed or use Hayseed-stuffed ones.
A list of some individual electrolytic caps.
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yea. I can't absolutely guarantee just by looking at it that its bad, but I've never had one visibly leaking that was not electrically in bad shape.
The caps develop electrical leakage, make heat, and that makes pressure so the magic goo starts to come out through the vent that is present specifically to give them somewhere fail rather than exploding and launching metal bits all over the place.
Fisher 800-C Re-Cap Kit
Hayseed Hamfest manufactures brand new multi-section can capacitors and re-cap kits for the Fisher 800-C.
hayseedhamfest.com
has a drop-in set for this specific model. The two extra caps are for the bias supply which I don't think you need. Can probably contact them and get it re-quoted without the radial caps.
I replace all cap cans on vintage units. You can bet they sweat all their electrolytic fluid.
If you pick up a new can and compare it to the old one, it's twice or more times heavier. Same mfd sections and voltage rating.
If you want to save yourself some money, identify the sections of the can that are bad, disconnect them from the circuit and replace them by undermounting them. Refer to the service manual for the values.You can keep the original can in place for aesthetics. It’s the easiest and cheapest solution, assuming you have the tools and skill set.
On the 800c, the most complicated can has 4 caps; the simplest has only one.
On the 800c, the most complicated can has 4 caps; the simplest has only one.
Before the more invasive solution, power receiver, reproduce the hum, and squeeze the power transformer. If the hum changes, simply tighten the bells of the transformer until the hum disappears.
As a matter of course, I ALWAYS replace those cans, whether needed or not. All I’m suggesting is that they may not be the cause of the hum.
Transformers normally vibrate and, over time, the potting hardens and the bolts loosen resulting in a soft, almost imperceptible hum or buzz. Mechanically tightening things up corrects that issue. That said, I never trust the cans and re-stuff them in every single Fisher that I’ve owned, no questions asked.
While we’re on the subject of cans: if the can with the black ooze is the cardboard covered can, then the black gunk is not electrolytic but the tar used to attach the cardboard cover to the can. When you dissect a bad can cap, you won’t find anything black but, rather, a white pasty electrolytic encased in foil paper together with several metal conductive strips that end with the can’s terminals. An electrically “leaky” cap can definitively be determined only with an appropriate tester. Again, whenever I purchase a Fisher unit, I don’t bother to test for leakage. I take the position that they’re done due to age and replace them.
Transformers normally vibrate and, over time, the potting hardens and the bolts loosen resulting in a soft, almost imperceptible hum or buzz. Mechanically tightening things up corrects that issue. That said, I never trust the cans and re-stuff them in every single Fisher that I’ve owned, no questions asked.
While we’re on the subject of cans: if the can with the black ooze is the cardboard covered can, then the black gunk is not electrolytic but the tar used to attach the cardboard cover to the can. When you dissect a bad can cap, you won’t find anything black but, rather, a white pasty electrolytic encased in foil paper together with several metal conductive strips that end with the can’s terminals. An electrically “leaky” cap can definitively be determined only with an appropriate tester. Again, whenever I purchase a Fisher unit, I don’t bother to test for leakage. I take the position that they’re done due to age and replace them.
I'm betting the hum is 60Hz, not 120Hz, from the video. Usually, dried out filter caps = 120Hz. We'll find out.
Great info ^^ i used this to figure out a few hums in a few amps, turned out to never be a bad cap, but was a bad tube, one of them was on a set of Dynakit MK4's the 7199 was causing a hum. Tubes tested strong, I ended up swapping tubes from one amp to the other and it carried. Turned out to be a noisy 7199. This got me testing all my other amps, and sure enough on my Heathkit AA-30 one of the 7199s also had a slight hum.
trainbuffton
Active Member
They're large and expensive because they are made to the correct form factor for tube amplification. The reason they are mounted above chassis is ho keep them away from heat.
A tech can certainly mount smaller modern electrolytic caps under the chassis, but since you're paying him to do the job, make sure he does it right, with can style caps.
I've seen some extremely
Hinky cap jobs performed on things because someone didn't have, or didn't want to order the correct cap.
Often they disturb the ground current path of the power supply and you'll end up with too much hum simply due to improper routing of the power supply ground currents.
So in summary it's very important to do this right, which is why I'd order the hayseed caps and do it myself.
More recently I've given in to buying the more expensive cans that just drop in with no fuss. I balance it against time and effort involved, and what it looks like at the end of the day. Winging caps in something is easy, having it not look like you just winged caps into something is a bit harder. Flying splices and unsupported components are asking for problems down the road.
Plus, placing all the electrolytic caps under the hood may interfere with the wiring layout.
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yeah these things are busy inside. That can cap underneath can go and it gives more room. Someone was making a board that basically occupied that entire back corner for the caps but it really fills the space up.
I restuffed the caps when I did my Sherwood S-7000, that was pretty much the last time I restuffed caps because I decided I just didn't enjoy the process at all. No space in those things to stick caps underneath.
I restuffed the caps when I did my Sherwood S-7000, that was pretty much the last time I restuffed caps because I decided I just didn't enjoy the process at all. No space in those things to stick caps underneath.
These companies should have done what Fender did, putting the cap under a doghouse on top of the chassis. Replacing these caps is so easy.
Doghouse power caps.
Doghouse cover.
Space. Looks like a lot of open flat chassis on that Fender, not so much on receivers or honestly most hifi gear. Even the stuff that doesn't need to be cramped often is. I guess they were saving pennies on the steel in the chassis or something, but way too many things are just way more cramped than makes any sense. Makes them miserable to work on too.