I picked up an old heathkit O-11 at a garage sale for a few bucks. It seems to work but makes a slight sizzling sound and after being on for a few minutes emitts smoke. I think it is the caps in the power supply. Does anybody know if these units can be rehabed?
Well, sort-of. One, use your nose and eyes and see if you can locate the stinky part (do not turn it on). Usually the electrolytics need either forming or replacement; prolly too late to try re-forming. It is possible the problem is in the transformer, which is special - it has a rather high voltage winding for the CRT, as i remember. That winding has a tendency to break down, which results in what you discovered (but ther may be other reasons for the smoke). If the transformer is definitely the stinky part, then it is a very good bet that HV winding is bad. If you took the transformer laminations off, thenyou may get a better look to find out if that winding is the outer-most one. If so, then one could replace it, using better materials. Count the turns per layer for the first 2 or 3 layers, and the number of layers for the total turns. You can use thin mylar tape for insulation in place wher paper was used when you re-wind. When the transformer in my O-1 when bad, i ordered a replacement transformer from Heath (the O-1 was a kit still being sold then). Be advised that this project would be useful only for re-habilitation for working antique sales or other profitable purposes. The O-1, while better than a number of the other inexpensive kits and scopes at that time, you can get far better (used) scopes now for a cost less than the time involved for restoration.
Reforming, that's when you use a variac and warm up the unit at a lower voltage for a while?
CV
The large Astron can cap seems to have leaked. It's rated at 40mfd,
20mfd, 20mfd and 50mfd at 450 ,450, 450 and 300VDC respectively. When I turned it on, the first and only time. A green dot appeared on the tube and the controls seemed to affect it properly. Anybody want it for parts? Make me an offer :)
Aye-Yup! And crank up slowly.
In article , snipped-for-privacy@yahoo.com mentioned...
Some of the caps are over a thousand volts. They're filtering for the tube's high voltage.
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I'd stick with paper, if the proper kind is used it would be better for a transformer that's in hot tube equipment.
Really. And they won't be using toobs. One thing that could be donw is if the high V winding is the problem and the rest of the transformer works okay, then use a tripler or more for the high V.
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The problem is, that there are shorted turns in the transformer - which will mwke it overheat. So one should *not* use it!
I have seen a lot of these old Heath, Eico and RCA tube scopes with a separate filament transformer added because the insulation was breaking down in the original transformer, and people used them daily, for years.
-- 9 days! Michael A. Terrell Central Florida
The transformer in the Heath supplys everything, and if the CRT HV winding goes, then it needs replacement or re-winding.
Robert, i have disconnected the separate 6.3 volt winding from the CRT and replaced it with a separate transformer and had it work quite a few times. I've done it to Heath, Eico, RCA, and other brands. It depends on the problems in the original transformer, but its a lot better than trashing a scope if you don't have another to replace it with.
-- 8 days! Michael A. Terrell Central Florida
Well, like i said, there are a number of windings on the power transformer, and all of the failures i saw and/or experienced were related to the CRT high voltage winding. If there was arcing in any of the HV windings, or arc-over to any other winding, it is not safe to use the transformer without complete repair/replacement. Now, if (somehow) a filament winding fails open, *then* your strategy is acceptable.
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