Hi All,
I continue my learning journey into electronic and vintage amplifier. With the help of @Moolie, I brought back to life a Sony STR-6045.
It was all working well including AM/FM except for this little stereo lamp indicator that would not light up.
I traced the problem back to a few transistors when I decided to measure the capacitors in this area while I was at it. There was one capacitor I could not test (the service manual called it “Styrol”). I said to myself, let’s desolder it without investigating further what it was. Stupid me! 😡 I discovered that these Polystyrene caps have very fragile leads and managed to break one.
It seems that it can now be replaced nowadays by Polypropylene caps or Ceramic (NPO COG) depending on its usage.
I see a few threads on DIYAudio.com but they are now getting old, so I thought I would ask. My question to you all, is what is it used for exactly and what would you recommend as a replacement?
This styrol capacitor (C320) is on the input of the transformer (T301) on the schematic.
Some more details from the manual for those of you interested:
Thank you all in advance for your help and precious advice.
I continue my learning journey into electronic and vintage amplifier. With the help of @Moolie, I brought back to life a Sony STR-6045.
It was all working well including AM/FM except for this little stereo lamp indicator that would not light up.
I traced the problem back to a few transistors when I decided to measure the capacitors in this area while I was at it. There was one capacitor I could not test (the service manual called it “Styrol”). I said to myself, let’s desolder it without investigating further what it was. Stupid me! 😡 I discovered that these Polystyrene caps have very fragile leads and managed to break one.
It seems that it can now be replaced nowadays by Polypropylene caps or Ceramic (NPO COG) depending on its usage.
I see a few threads on DIYAudio.com but they are now getting old, so I thought I would ask. My question to you all, is what is it used for exactly and what would you recommend as a replacement?
This styrol capacitor (C320) is on the input of the transformer (T301) on the schematic.
Some more details from the manual for those of you interested:
Thank you all in advance for your help and precious advice.
That capacitor tunes the circuit to 38kHz, so the value and precision is important.
Use a low inductance polypropylene film type, with short leads.
The T301 adjustment may need to be retuned after capacitor replacement.
Use a low inductance polypropylene film type, with short leads.
The T301 adjustment may need to be retuned after capacitor replacement.
Ouch! I was trying to avoid a retuning has I don't have a scope yet and I'm being told, it is not easy. Thanks for the advice. When choosing polypropylene is it better metallized or pure polypropylene?
Is 6 nH/cm for the total length of capacitor winding and the leads considered low inductance? Not all datasheet list the inductance.
Is 6 nH/cm for the total length of capacitor winding and the leads considered low inductance? Not all datasheet list the inductance.
Whichever cap you use will have to properly fit the pcb without much extra lead length, so radial style.
This PS radial foil cap may work ok. For an extra charge they'll sort to a better tolerance.
Expensive, but at least there's only one of them. Parts Connexion doesn't have any.
And don't mess with any of the others, either. You've been warned.
https://www.soniccraft.com/product_info.php/rte-4700-pf-400vdc-p-326
This PS radial foil cap may work ok. For an extra charge they'll sort to a better tolerance.
Expensive, but at least there's only one of them. Parts Connexion doesn't have any.
And don't mess with any of the others, either. You've been warned.
https://www.soniccraft.com/product_info.php/rte-4700-pf-400vdc-p-326
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Thanks for link. You are saying that I can ask them to match it to my measurement on the broken leg capacitor? (i.e. 4590 pf)
And don't worry, I will never touch any of those again!
And don't worry, I will never touch any of those again!
You can ask them, and they'll tell you what they can do. That's about 2% low, if your tester is good.
Allow for the test fixture lead capacitance, unless you zeroed it out..
Check first to see how the radial leads will fit the pcb footprint.
Allow for the test fixture lead capacitance, unless you zeroed it out..
Check first to see how the radial leads will fit the pcb footprint.
Polypropylene may not be stable enough for RF oscillator service, I suggest going with NP0 / C0G. You need a low tempco so things stay in tune as the box warms up.
Polystyrene is below its glass transition temperature so is mainly crystalline, whereas PP is above it and rubbery, leading to higher thermal expansion for one thing.
PPS might be another candidate.
Thank you all. It seems I'm starting to have some interesting options. The real thing at Sonic Craft if lead spacing is okay and shipping cost to Canada does not make it prohibitive is probably the best one.
If not, I will order a few NPO/COG and PPS and select the closest match in capacitance.
If not, I will order a few NPO/COG and PPS and select the closest match in capacitance.
Not cogent to this thread, but when that piece came out, it was very well regarded and reviewed: especially at the price. The tuner was very good, the amp almost and afterthought>
Your cap, a polystyrol cap, has a negativ temperatur coefficient that almost matchs the positive tempco of the coil and thus keeps the resonant frequency almost temperature undependend. Use a polystyrol cap as replacement, it is the best solution to your problem. RIFA, a swedish company, made such caps (now owned by Vishay, i thinck)
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This discussion is getting even more interesting. Although everyone agrees that the best replacement is with the same material, some thinks capacitance stability is important, some thinks negative tempco is. Not sure how high the temperature can gets but I read that polystyrene does not support more than 85 degrees C. According to this graph, it seems capacitance of Polystyrene can not drop more than half a percent. Polypropylene would be about 1% at 85 C.
In the 50 degrees range, the difference seems negligible.
I'm almost tempted to turn this problem into an experiment where I would test with different type of capacitors!
In the 50 degrees range, the difference seems negligible.
I'm almost tempted to turn this problem into an experiment where I would test with different type of capacitors!
Not negligible in critical circuitry.
https://www.rfcafe.com/references/e...lm-capacitors-electronics-world-july-1965.htm
https://www.rfcafe.com/references/e...lm-capacitors-electronics-world-july-1965.htm
It has been a while so I thought I could provide some updates. After all, I decided to not pursue my experiments and just purchase the real thing. Fortunately, I was able to find a polystyrene capacitor for cheap at Mouser that measured 4600pf. Close enough to the 4590pf one that I needed to replace.
No significant difference in the tuning so I don't think an alignment will be necessary. I'm just missing 2.2V on the stereo light but this will be the subject of another post.
Thank you all for your assistance and valuable opinions on this thread.
No significant difference in the tuning so I don't think an alignment will be necessary. I'm just missing 2.2V on the stereo light but this will be the subject of another post.
Thank you all for your assistance and valuable opinions on this thread.