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 Post subject: Unusual elecrtolytic ...well at least to me
PostPosted: Oct Thu 12, 2017 2:22 am 
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I picked up a nice little Knight KG 221A at the antique mall the other day. I have replaced the 3 electrolytic filter caps, but there are 3 other very small ones ( I guess they are electrolytics) in the radio also.
This radio is circa 1965, so about 10 to 15 years newer than I am used to working on.

In the center of the photo below you will see a 10uf 25V cap (black with one red end and one yellow end), there are two others, a bit out of view to the left and right. The other two are both 2uf.

What are these? I assume that I should change them, but I would like to know more about them.

Thanks!

Russ


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 Post subject: Re: Unusual elecrtolytic ...well at least to me
PostPosted: Oct Thu 12, 2017 3:41 am 
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Yes, change these electrolytic caps. They do not have safety vents. If these caps overheat they go off like a fire cracker.

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 Post subject: Re: Unusual elecrtolytic ...well at least to me
PostPosted: Oct Thu 12, 2017 3:43 am 
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The one on the left is definitely an Electrolytic, and with what little that I can see of the one on the right, I assume that it is as well.

Replace with the modern equivalent (2.2 uF).

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 Post subject: Re: Unusual elecrtolytic ...well at least to me
PostPosted: Oct Thu 12, 2017 12:25 pm 
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Thanks Norm and fifties!

I just checked my stock, I have both values available, but they are 450V. Is there any downside to using these?

Russ

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 Post subject: Re: Unusual elecrtolytic ...well at least to me
PostPosted: Oct Thu 12, 2017 2:04 pm 
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Those were called Catlins. They are hard plastic cased electrolytics which were popular in the early to mid 1960s. Both acial and radial lead versions were made. They had extremely low ESR achieved through the use of a more volatile electrolyte. The electrolyte attacked the metal tubes ordinary electrolytics are housed in, which is why they went to hard plastic tubes. Unfortunately the plastic did not do a good job of keeping the electrolyte in, so those caps are nearly always dried out and dead today.

The small 2.2 uF caps are probably not filters; they are probably in the ratio detector and output bypass circuits. Nevertheless the radio will almost certainly perform better if you change them.

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 Post subject: Re: Unusual elecrtolytic ...well at least to me
PostPosted: Oct Thu 12, 2017 5:01 pm 
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Chris108 wrote:
Those were called Catlins. They are hard plastic cased electrolytics which were popular in the early to mid 1960s. Both acial and radial lead versions were made. They had extremely low ESR achieved through the use of a more volatile electrolyte. The electrolyte attacked the metal tubes ordinary electrolytics are housed in, which is why they went to hard plastic tubes. Unfortunately the plastic did not do a good job of keeping the electrolyte in, so those caps are nearly always dried out and dead today.

The small 2.2 uF caps are probably not filters; they are probably in the ratio detector and output bypass circuits. Nevertheless the radio will almost certainly perform better if you change them.


C A L L I N S - that's the brand. 1068 RMA code. Zenith used them for years - their number one failure item in big-screen TVs after sweep tubes./

Edit - Greenfield Tennessee is mighty proud of them:

https://www.callinscapacitors.org/capac ... hibit.html

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 Post subject: Re: Unusual elecrtolytic ...well at least to me
PostPosted: Oct Thu 12, 2017 6:00 pm 
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radioalfa wrote:
Thanks Norm and fifties!

I just checked my stock, I have both values available, but they are 450V. Is there any downside to using these?

Russ

No downside in using at least the rated working voltage or a greater value of it.

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 Post subject: Re: Unusual elecrtolytic ...well at least to me
PostPosted: Oct Thu 12, 2017 8:51 pm 
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Really? Did you look at the circuit (available at http://www.bama.edebris.com) to see how these caps are actually used? One of the 2-uF caps is in the base of a transistor squelch circuit with 0.62 volts on it. The 10-uF is in the collector of the same circuit with 0.5 volts on it. If you use 450-volt electrolytics in these locations they will not stay formed and in a year or two they will develop enough leakage to prevent the squelch from working.

The last 2-uF is a cathode bypass for the output tube with 20 volts on it. That's a little better but still massive overkill if you put a 450 volt cap there. Just replace the parts with the original values. Knight over-engineered this product to a huge degree, you don't need to do any more.

NB: Catlins was a Japanese knock-off of Callins used in some products. They did not hold up any better.

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 Post subject: Re: Unusual elecrtolytic ...well at least to me
PostPosted: Oct Thu 12, 2017 10:56 pm 
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Thanks Chris, I'll put the 450's back in the box and get some closer to the proper voltage rating.

Russ

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