Hello. Once again I am coming to the well to seek advice from those who don't mind assisting a relative novice. My question(s) are simple, please refer to the enclosed schematic (HK Citation 16A, output section), C3 and C4 (both 10uf 150V).
1. These serve as "bypass" capacitors? If not then?
2. I don't have polarized electrolytic in stock, but I do have non polarized 250V polypropylene in 10uf. Can I safely (and without unintended circuit consequences) substitute?
3. Lastly, electrically, it doesn't matter where on the respective supply rail they are located?
Thank you in advance. I appreciate you help
1. These serve as "bypass" capacitors? If not then?
2. I don't have polarized electrolytic in stock, but I do have non polarized 250V polypropylene in 10uf. Can I safely (and without unintended circuit consequences) substitute?
3. Lastly, electrically, it doesn't matter where on the respective supply rail they are located?
Thank you in advance. I appreciate you help
These capacitors usually are located near the output transistors to provide current for fast transients directly to the output transistor while the current backfills through the wire from the main filter cap. 8" wire above a metal surface has about 72 nH inductance.
A 10 uf polyprophylene cap costs 10 or 20 times what an electrolytic does. It may have more self inductance than the electrolytic because it is so much larger. Inductance slows the ability of the current to flow quickly. You should order a new electrolytic along with the other parts to update them to save on freight. It costs me $9 to get one box of parts from a distributor. Local parts stores are dead, but when they operated they sold me a lot of short life garbage caps. You show as being in USA. I use newark (SC), digikey (MN) or occasionally mouser (TX). Mouser makes me read each datasheet to determine the service life of each cap. Newark used to put the service life in the selector table. Have been recent changes to the Newark selector table I don't like. I usually install e-caps with no less than 3000 hours service life, 10000 if I can get it. Garbage e-caps from local store lasted only 8 years.
Look at the date on the parts; it is unlikely these capacitors are original. If you have a meter, read ESR of the electrolytics. They may not be bad. You need to disconnect the Collector rail from the main cap to get a local cap reading. The Peak ESR meter comes wtth a table of standard ESR for various sizes and voltages. I cannot read it to you because mine was stolen.
A 10 uf polyprophylene cap costs 10 or 20 times what an electrolytic does. It may have more self inductance than the electrolytic because it is so much larger. Inductance slows the ability of the current to flow quickly. You should order a new electrolytic along with the other parts to update them to save on freight. It costs me $9 to get one box of parts from a distributor. Local parts stores are dead, but when they operated they sold me a lot of short life garbage caps. You show as being in USA. I use newark (SC), digikey (MN) or occasionally mouser (TX). Mouser makes me read each datasheet to determine the service life of each cap. Newark used to put the service life in the selector table. Have been recent changes to the Newark selector table I don't like. I usually install e-caps with no less than 3000 hours service life, 10000 if I can get it. Garbage e-caps from local store lasted only 8 years.
Look at the date on the parts; it is unlikely these capacitors are original. If you have a meter, read ESR of the electrolytics. They may not be bad. You need to disconnect the Collector rail from the main cap to get a local cap reading. The Peak ESR meter comes wtth a table of standard ESR for various sizes and voltages. I cannot read it to you because mine was stolen.
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Yes, I use all the vendors mentioned and Parts Express as you just can't trust anything on the internet, especially eBay. Learned that hard way with 2916 tranny's not long ago. I do not have an ESR and should probably invest in one. The caps on both channels are original 1976, 38th week and interestingly above spec 250V. Like I said, I have the poly's collecting dust and fitment won't be an issue so why shouldn't I consider it was my thought. Inductance concern duly noted, will dig into the caps I have a bit more. Thank you for the reply.
A 2 or 3 x size polypro would affect the measured slew rate, which is a sales point of an amp design. You may not hear the difference versus a tiny e-cap, unless you listen to a lot of explosions in movies. Vertical edges have lots of high frequency content (fourrier transform). A 1976 e-cap is definitely at risk of shorting out. The polypro at 150% voltage rating never will.
