Warm electrolytics?

[Jonathan]

My CTC9 uses two 160uF 350V electrolytics in it's voltage doubling circuit. After a while, these capacitors get a little warm (not hot), but the sound (which is the only thing I could test) still performs fine. it's not hooked up to the picture tube and the horizontal oscillator and output tubes are removed. I put a new 160uF 350V electrolytic in, and left the multicap 160uF/50uF/50uF in. Both get warm to the same degree. Could the multicap be bad? Is this normal for these to get warm?

Thanks.

Jonathan

[andy]

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[kx250rider]

I agree with Andy... Of course the best thing would be to disconnect and test each section with a leakage-at-working-voltage checker such as a Sencore LC-101. But if that isn't feasible, here's what I'd do: With the chassis totally cold, power it up. Wait about 5 minutes, and see if the can is warmer than the rest of the stuff around it. I wouldn't want it warm that fast. But if it seems to be cool at 5 or 10 minutes, but then after a half hour it's warm (BUT NOT HOT), that's probably safe. And when Andy says "VENT", that can be a polite synonym for "EXPLODE" in some cases

Charles

[vintagecollect]

consider investing in good cap tester with eye tube. Tester that will apply working voltage and or power rating checks caps for leakage present. This will simulate caps working condition. Replace if value is too high or shows any leakage. Risk to power transformer and other parts too great!

[Randy Bassham]

I once had an 80/80/20 at 475 in a Magnavox T962 chassis vent right past my left ear. I had just turned the chassis over and was trying to find the reason for the circuit breaker tripping intermittantly when the whole bottom blew out of the can and the stuffins went past my left ear. This was around 1975 and the set would have been a little over 3 years old at the time. I'm in the middle of restoration of a Sansui 1000A and I've got a 20/20/20 at 500 heating up badly, I'm having trouble finding replacements with greater than 450 working volts, since the B+ on one of the sections runs up to 485 volts during warmup and seems to be running about 430 or so on that section it really needs the higher rating.

[Chad Hauris]

We have gotten new 20 mfd at 500 volt Sprague caps at our shop...just used some in a Leslie amp repair. I think we got them from New Sensor. I think they also have a JJ dual cap with 50 and 50 mfd. at 500 volts and we have used these successfully too.

[kx250rider]

I think the Newark catalogue has 500_plus volt cans... Not cheap, but at least they had them within the past year or so.

And there are newly-made 20-20-20-20 @450 cans available from Antique Electronic Supply in Tempe.

Charles

[Big Dave]

I expect cans near tubes to get slightly warm. Anything beyond "slightly warm" is history. If a cap is beyond "slightly warm during soft start, I immediately abort the soft start and recap.

[Jonathan]

Thanks guys. Two problems solved with one thread. I ended up replacing all electrolytics. The chassis is working the way it did, so it seems like the electrolytics never needed changing but atleast they are brand new. The tube sockets on the pcbs seem to really suck. Are they known for failure? Also, the video amp, it won't light up. It uses a 12V filament that is center tapped; the tap gets connected to ground and the two ends get connected to the filament winding. I looked at the resistance of the filament and it's 6 ohms, and 3 ohms at each end from testing from the center tap. What do you guys think it is? And also, portions of the video cause noise in the audio, but it might be because of that tube socket.

Thanks.

Big Dave,

I saw your site. It rocks. I saw that with your roundies, the most capacitors you replaced are pretty much the electrolytics, and only replaced the others like on the vertical oscillator board because they were suspect. Is this usually pretty much it that needs to be changed other than suspect parts?

Thanks.

Jonathan

[Big Dave]

On the 16, it used mylar caps. I was having trouble getting the vertical to fill the screen. Most of the 60's era sets will use mylar. The CTC-9, I believe used black beauties. They are evil and must be replaced. AES sells PC mount tube sockets. I had to replace one on my 16. I have not taken my 9 apart yet. It looks to be in overall very good condition. The most I did was soft start it and check the CRT. My other round color sets have the original parts. I did replace the lytics in the round Zenith several years ago, but I replaced the cans with exact replacement cans. Not a good move, as the cans probably were a few years old then.

With 50's era sets, all paper and electrolytics must be replaced.

As far as the 12 volt vid out tube, resolder the socket. Then again, the tube may have gone south. I still have more resoldering to do on the color board on the 16.

Thanks for the words about my site.

[Chad Hauris]

I have heard of cases on RCA CTC-16's where the circuit board to chassis ground connections go bad causing open connections in the filament circuit.

[Jonathan]

Big Dave,

Even though the filament has resistance? I ordered some new sockets anyway, and a new tube. And the black beauties (specifically, in the horizontal board, video IF board, and across the AC line) I changed except for the one on the video IF board. I guess I just have to wait for the order, install the capacitor and sockets and hope for the best.

Chad,

The video output board has good ground contact, it's either the tube or the socket.

Thanks guys.

Jonathan

[pallophotophone]

Ever see a 80 mfd 450 v lytic loose it, blow the can off the works- pass through 2- 3/4 inch thick drywalls and finally smash itself flat on a brick wall 15 feet away from the second drywall ?
I did - Darned scary and impressive. Hope to never see it again.
Why the fiber bottom didn't let go first, I'll never know.

Truth being stranger than fiction...

Bob Hodge

[bgadow]

I have one old boat anchor that uses cans that are something like 10 @ 600 volts. I haven't figured out a source for them yet.

[Chad Hauris]

You can put 2 22 mfd 450 v. caps in series , connecting the (-) of the first to the + of the second, to make an 11 mfd 900 volt cap. You also need to put a resistor across each cap (100K if i remember correctly) for voltage equalization.
Also the exposed part of the can of the first cap will be "hot" so it should not touch anything. We did this in an RCA PA amp with 807 tubes which had very high voltage electrolytics and it has worked great.

Here is an article about it:

http://www.nostalgiaair.org/referenc...d/rsd0944b.htm