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rca-victor: RCA Victor 9Y5 Silver Mica disease, repair

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Forum » Radios and other type of sets (Physics) etc. » MODELS DISPLAYED » rca-victor: RCA Victor 9Y5 Silver Mica disease, repair
           
Vincent Cappuccitti
 
 
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15.Mar.19 18:48

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I am repairing an RCA Victor 9Y5 radio/phonograph that I beleive has silver mica disease. I need to know what capacitor values I should use for the 1st and 2nd IF transformers if I repair it. Specifically C-18, C-19 and C-9, C-10.

These values are not shown on the schematic and being new to radio repair I do not have much test equipment. I do have hand held multimeters and capacitor tester.

I was hoping that someone may have had similar experience with these type radios and could recommend the proper capacitor values. This radio is very similar to the RCA Victor console radio model 9W501.

I have read that some people replace these IF trans. with all 100pf values with good success but I'm hesitant to do so because I've seen many scematics with values as low as 30pf .

Any recommendations would be greatly appreciated. Thank you in advance.

Rolf Beckers
Rolf Beckers
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15.Mar.19 19:30

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Dear Vincent,

These caps are somwhere in the range of 50 to 100 pf, depending at the inductance of the IF coil.

Try a 50  pf and check if you can do the alignment with the core of the IF coil.

Regards,

Rolf

Michael Watterson
 
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16.Mar.19 15:48

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What symptoms lead you to suspect it?

You are best to make sure everything else is fine. Often all the IF capacitors are the same value, except sometimes the diode side of the last transformer.

A 47pF NPO ceramic is close enough to 50pF (voltage rating isn't important). However if you have and inductance meter and know the IF frequency, the capacitance can be calculated. Polystrene are also suitable, but are easily damaged by soldering heat. Use flat pliers as a heatsink on capacitor side of the lead.

Vincent Cappuccitti
 
 
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16.Mar.19 17:02

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Dear Rolf,  thank you kindly for your quick response. I have removed one of the IFs and will purchase some capacitors to try.

Best regards,

Vince

Vincent Cappuccitti
 
 
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16.Mar.19 17:23

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Michael, it may be that I am making an assumption that it is the IFs that are causing the crackly static that the radio is exhibiting.

I have watched several youtube channels that have audio of SMD and my assumption is based on the similar sound characteristics that I hear with my RCA Victor.

If you feel I should focus my troubleshooting efforts elsewhere I am open to your suggetions. Below are some symptoms.

-This radio is able to bring in strong stations clearly, albeit with the background crackling.

-The crackling static is responsive to the volume control. less at low volume, more at high.

-The tone control tends to mask the Crackling static if adjusted to full bass.

-When the radio switch is turned to Auxillary or phono  there is no crackling static.

I will look for an inductance meter or purchase one if it will be a good addition to my meter family.

Thank you for your assistance. Looking forward to any other comments you may have.

Best regards,

Vince

 

Michael Watterson
 
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16.Mar.19 17:37

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I'd thought it was pre-1945 US sets that had this problem. It doesn't sound like IF.
Have you another set you can tune to the same station to rule out interference?

Have you tried turning all lights and appliances off, including any "networking over mains"? LED PSUs and CFL electronic ballasts are bad.

All the symptoms you decribe can be RF borne or mains wiring born interference.

The general purpose meters with bare PCB, ZIF DIL socket, 9V block battery and graphic LCD that test capacitors, inductors, resistors and semiconductors (showing circuit symbol and pin connects) on eabay from Hong Kong / China are good value. I've bought three, two for friends. They take about 6 to 8 weeks to get to Ireland.
 

 

 

Steffen Thies
 
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21.Mar.19 16:45

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Vince (and Michael), I think you already in good hands. Indeed silver mica disease is a much too popular diagnosis often applied to sets that don't have such capacitors. And your symptoms do not point there, too.

Before ripping apart the filters, please do check if they tune correctly. You may use a grid dipper with them still sitting in the set or simply see if you can align the set. If that works, there is only low probability they are faulty.

Generally, filter capacitors are not prone to crackling, because there's no DC load on them. You should look for all parts with high voltage across them. That may well be high point coupling caps in band pass filters, but don't forget the classics: Screen grid buffers, dirty tube sockets, ...

 

Best regards,

Steffen
 

Vincent Cappuccitti
 
 
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26.Mar.19 04:33

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Steffen and Michael, thanks for your input and recommendations. I have replaced a few of the ceramic capacitors and resoldered some connections that did not look good. Cleaned all of the sockets and switches.

The radio will work well for 10-20  minutes then the problem will reoccur. I haven't had much time to work on it lately but will investigate further this week when time permits.

Best Regards

Vince

Vincent Cappuccitti
 
 
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30.Mar.19 05:02

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Thanks to all that have helped me solve this problem. It does seem that the problem is from noisy lines as the radio worked perfectly for a full day while my wife was not home. No  TV's , computers, ovens, dishwashers ,washing machines, mixers were on or running.

As soon as the dishwasher was turned on late that night the problem returned.

The radio has been put back together finally! Now time to repair some veneer.

Best regards,

Vince

  
rmXorg