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Kuba Serenade Stereo Console - Part III - Replacing all caps

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Hello everybody,

I am starting a new thread again on the same old project as it's been abandoned for couple of months and nobody will follow back. I am sorry if that is not advisable, I'll correct that if needed.

The original threads is here:
Kuba Serenade Stereo Console question.
Kuba Serenade Stereo Console - Part II - New development - amp debug question

I am uploading the closest (but NOT EXACT!) schematic for reference here as well.

First - thank you to everyone who participated in the discussion and for valued advices! Really appreciated!:worship:

After the last talk I've decided that it's better top spent some time and recap ALL caps, not the suspicions and electrolytic ones - ALL OF THEM!

I've tried carefully to check all the values from the labels. As much as I remembered the rules - I got most of the values, but some of the caps are other without label or have color coding. One component I am not sure about at all if it is a cap, some of caps measure value I can't tell... in short - I'll need expert's help here, again...

OK, in details:

1. Photo 1:
This is the biggest cap of the type (film cap?). The label have been burned out originally, what I can see is "...000J" on most right side of the label. When removed the cap showed around 7 nF. Should I assume the value of 10000pF (10 nF)? It's in SW radio rail, but at least on the schematic I can't find cap with such a value... do you think 10nF should be fine?

2. Photo 2:
Two components in question:
A) The cap with color code at the left. I did my best searching the codes (I assume it's Ceramic Camp?) and I am reading it 15 pF/200V. Am I right? Should I replace it just in case or to remove and measure?
B) The black cap at the top (assuming it's a cap). It reads 4700, 500- 61C. I am reading it as 4700 pF, 500V DC, 61 degree rating - am I right? The problem is when removed and measured - it shows around 225 nF. Any ideas whaty happens here, why it's such a huge difference in measured and listed value, leak, dry, short...?

Photo 3:
Th two color coded caps - as on Photo 2 - I am reading them as 46 pF, 300V, am I right?

Photo 4:
This is the biggest question - you can see one cap I am reading as 300pF/500V, one green inductor (with wire on it) and one unknown gray component with only marking "3" on it. Any idea what is it? Note - it's in FM section which doesn't work, so I am trying to eliminate any suspicions component.

Any help will be appreciated!
 

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#1 is a small value polystyrene capacitor.

#2 A: Looks like a resistor. I might not be looking at the right part though.
B: looks burnt, so one would not expect it to measure accurately

#3 Confirm with a capacitance tester.

#4. Measure the thing with the "3" with an ohm meter, then resort to capacitance check if needed.
 
Hey,
Sorry, but please do not replace everything because it could be a faulty capacitor. There are some padding-caps which determine the intermediate frequency. You will have to balance/adjust the whole circuit with a sweep generator.
Generally speaking, there is no need to replace ceramic caps. I never had a faulty polystyrene in my life and restored lots of those radios. Just the burned one is a problem, I agree.

One you HAVE to replace is the black one in the second pic. Thats a real crap. The reason for the high capacity is as follows. The old resin becomes faulty and shows lots of cracks. Water vapor enters the cap and the paper dielectric. But: Water has a very high ε and thus increases the capacity. Sadly it also leads to leakage currents !
If you have caps of the following brand/type, then change them:
kondensator.jpg


Don't just swap parts ! You have to measure and measure and measure again. Did you fully understand the circuit ? FM uses a ECC85 as tuned amplifier synced with a self oscillating mixer. Did you check the self oscillating mixer ? It has to oscillate exactly 10,7Mhz higher than what the dial says.
Good Luck !
 
Guys,

Thank you for the valuable advises - I've ordered some of the caps that definitely need replacement and will start with them, not with all.

I've ordered them am I am waiting to receive the package and replace.

About the FM tuner - stocktrader200 and others - I have DC 102V DC on pin 6. The tube I put is brand new....
 
You need to check the FM oscillator. There is a clever trick which works as follows: One of the ECC85 systems is the oscillator which works on the frequency which is shown on the dial+10.7Mhz. You now need a second receiver which should be near your Kuba Serenade (same room). A superheterodyne is absolutely prefered. Tune that second radio to a station near the highest receivable frequency. It is advised not to use a very near/strong station. A faint signal is fine. You tune your Kuba Serenade now to the frequency of the station on the second radio MINUS 10.7Mhz. Your second receiver is now tuned to the Kuba's oscillator. If the oscillator works, it should mute your second radio. To get better results, you can solder a 3" piece of wire to the anode connection of the socket of this oscillator tube which will act as antenna. Only a little piece...otherwise it will add capacity or other bad effects (Lecher lines - Wikipedia, the free encyclopedia)
That's an easy way to test that oscillator
 
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