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 Post subject: GRAETZ 616 CAPS QUESTION
PostPosted: Aug Fri 12, 2022 7:14 pm 
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Joined: Apr Sun 10, 2022 6:28 pm
Posts: 63
Hi,

Just bought a GRAETZ 616. It works well on AM and Shortwave but I noticed the FM was distorted. I replaced the EL84 tube with a new one and the sound became better but would fade and now it bad again. The paper caps beside it were melted with big blobs, so I will replace them.
The other capps look okay. Should this fix the issue? See photo.


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 Post subject: Re: GRAETZ 616 CAPS QUESTION
PostPosted: Aug Sat 13, 2022 7:01 am 
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Location: Aurora Colorado
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I would order all of the caps, that you do not have and begin to recap the set.

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 Post subject: Re: GRAETZ 616 CAPS QUESTION
PostPosted: Aug Sat 13, 2022 2:07 pm 
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Joined: Jun Fri 19, 2009 5:34 pm
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Location: Floral Park, New York
The old paper caps may still be good or they may not be, but there is absolutely no way to tell just by looking at them. They would have to be tested for capacity, leakage, and AC losses using one or more bridge type instruments. I usually pick two or three capacitors at random and test them; if they are still good I continue testing and only replace any individuals which have to be replaced.* But if the first two or three all turn out to be equally bad, I assume they all are and don't waste my time testing more of them.

If you do not have the equipment and the time or patience to do this kind of testing you are on safer ground to just replace them with the nearest commercially obtainable values, but never go less on voltage; always go higher if you can't get the same voltage rating. If deteriorated, old capacitors can break down unmercifully and cause resistors, transformers, and other parts to fail.

As for FM distortion it is possible that a paper capacitor might be responsible, but it is more likely that the ratio detector or discriminator capacitor is bad. This is usually a small electrolytic cap, about 5-uF often rated for 50 volts or less. Because they are so small they tend to dry out faster than bigger electrolytics and when they are kaput the AGC voltage follows the audio. This causes a form of degenerative feedback which makes the audio distorted.

*There are certain exceptions to my rule. Any paper capacitor across the AC line or from AC line to chassis, used as a coupling cap to an output tube, or from the plate of an output tube to ground gets replaced regardless of how it tests. Same goes for vibrator buffer caps and any connected to the HV winding of a power transformer.

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 Post subject: Re: GRAETZ 616 CAPS QUESTION
PostPosted: Aug Sun 14, 2022 1:54 am 
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Joined: Apr Sun 10, 2022 6:28 pm
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I agree it’s probably best to replace them all. Thanks very Much!


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 Post subject: Re: GRAETZ 616 CAPS QUESTION
PostPosted: Aug Sun 14, 2022 2:49 am 
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Joined: Apr Sun 10, 2022 6:28 pm
Posts: 63
Is one of these in the photos below the ratio detector or discriminator capacitor?


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 Post subject: Re: GRAETZ 616 CAPS QUESTION
PostPosted: Aug Sun 14, 2022 2:49 am 
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Joined: Apr Sun 10, 2022 6:28 pm
Posts: 63
or this?


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 Post subject: Re: GRAETZ 616 CAPS QUESTION
PostPosted: Aug Sun 14, 2022 2:50 am 
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Joined: Apr Sun 10, 2022 6:28 pm
Posts: 63
or this??


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 Post subject: Re: GRAETZ 616 CAPS QUESTION
PostPosted: Aug Sun 14, 2022 2:51 am 
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Joined: Apr Sun 10, 2022 6:28 pm
Posts: 63
Finally, i assume this is a resistor and not a cap?


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 Post subject: Re: GRAETZ 616 CAPS QUESTION
PostPosted: Aug Sun 14, 2022 3:12 am 
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Joined: Apr Sun 10, 2022 6:28 pm
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The diagram I have says this one is 50 uf. I’m thinking this has a burnt top. Should I replace?


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 Post subject: Re: GRAETZ 616 CAPS QUESTION
PostPosted: Aug Tue 16, 2022 1:29 am 
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Joined: Feb Tue 24, 2009 7:20 am
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Location: Aurora Colorado
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It is hard to offer help, without a coppy of the schematic, or a clipping of the area in question. I have found though ,
that those poly/styrene clear plastic caps tend to be fine. Maybe starting with the power supply, and test the set.

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