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[Bob Leonard]

Bob,

I must have been lucky with vintage tube amps, only one out of six needed caps replaced, and that was one of the "newer" ones, probably mid 1960s.

Bourns makes pots that are rated for a half million cycles, what are the CTS pots rated for?

Art

Art,
CTS pots are rated about the same. The deal with the CTS pots is that they are the pots Fender and Gibson used as OEM hardware pretty much from day one. That has induced a cult following of sorts.

You must be a very lucky person indeed. I have never seen a 50 year old electrolytic that didn't need replacement for one reason or another. Outward appearance aside, electrolytic or not, caps don't last forever. Even the coupling caps in old amps should be checked for back voltage, and electrolytic caps should be measured and tested if you don't intend on replacing them. Tone caps aren't the real issue, and many people can live with lousy tone. It's the power supply filter caps, bias caps and coupling caps, that can and will cause the most grief as Ned already mentioned. I can do an entire amp using quality caps for about $75 in parts, and guarantee there will be a huge difference in tone and performance when done. So, to each his own, but you might want to take a second look at those 50 year old caps.

[Ned Ward]

Just took my Bogen Challenger to my amp guy yesterday; Chris Fleming from the Fender Custom shop was there, and we talked mods as he loves these old PA's as well. Besides replacing the AC cord for a better non-frayed on and inspecting the grounding, the amp tech will change out the filter caps and swap the old Amphenol mic inputs for 1/4" inputs. Of course, I'll keep all these original parts in a baggie in case someone wants it original... may also look into replacing the 70 volt speaker outlets with a 1/4" speaker out and a impedance selector, per Chris's advice. Or may just get a good heavy duty speaker cable with spade ends to screw on to either 4 or 8 ohms depending on the cab.

[Mike Sokol]

I'm ordering some .047/600-V capacitors for my Stinger-GFCI experiments, and see a lot of NOS (New Old Stock) available. However, I know that paper capacitors will eventually dry out, so I want something that's as reliable as possible since it's a safety issue. What's your experience with caps like I've posted below. They could be 20 years old already, but these are sealed "dipped" capacitors. I've never seen one of these fail from age, but lots of you have seen way more old amplifiers than I have. 

Opinions, please...

[John Roberts {JR}]

I would pay $15 for a cap even if I had your money...

DIgikey has .047 uF 10% 630VAC 2000VDC metalized polypropylene... $3.67 each

http://www.digikey.com/product-search/en?pv1292=56&FV=fff40002%2Cfff80010%2C340021&k=X+caps&mnonly=0&newproducts=0&ColumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25



JR

[John Roberts {JR}]

The orange drops from digikey are only 200VAC 600DC

http://www.digikey.com/product-search/en?pv1293=35&FV=ffec605a%2C340021&k=orange+drop&mnonly=0&newproducts=0&ColumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25



$3.53 in onsey twosey...  But for 240VAC countries not up to the task IMO.

JR

[Frank Koenig]

I know there are film capacitors made for applications where leakage would result in a shock hazard. When I designed electrosurgical generators we were required (by FDA, or it could have been VDE or TUV, can't remember) to use such a highly pedigreed cap as the series capacitor in the high-pass filter in front of the probe that gets stuck into the patient. They're usually used in line filters and such and are in a prismatic, radial-lead, through-hole package that is plastered with agency approval marks, TUV, UL, etc. You probably know the ones.

I'm having trouble finding an example right now but I'll keep looking.

--Frank

[Frank Koenig]

I'm having trouble finding an example right now but I'll keep looking.

Like this: http://www.kemet.com/docfinder?Partnumber=R413F12200000M

[John Roberts {JR}]

I know there are film capacitors made for applications where leakage would result in a shock hazard. When I designed electrosurgical generators we were required (by FDA, or it could have been VDE or TUV, can't remember) to use such a highly pedigreed cap as the series capacitor in the high-pass filter in front of the probe that gets stuck into the patient. They're usually used in line filters and such and are in a prismatic, radial-lead, through-hole package that is plastered with agency approval marks, TUV, UL, etc. You probably know the ones.

I'm having trouble finding an example right now but I'll keep looking.

--Frank

Yup I couldn't find one either they were called something like X caps or Y caps for mains power applications.

OK we want a Y cap for line to chassis.

Y caps are metalized film so they are self healing in response to punch throughs.

Here is a proper "Y" cap.

http://www.digikey.com/product-search/en?s=19609&FV=fff40002%2Cfff80010%2Cfffc018f%2C340021&k=Y+capacitor&mnonly=0&newproducts=0&ColumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25



http://www.kemet.com/Lists/Filestore/EvoxRifaRFIandSMD.pdf

Here is a brochure about X and Y caps...  I didn't look hard enough before

BTW  300VAC, 1250VDC and only $0.97 for onsey/twosey.

JR

[edit] this is surely over engineered for the application, but at <$1 looks OK [/edit]

[Mike Sokol]

The orange drops from digikey are only 200VAC 600DC

$3.53 in onsey twosey...  But for 240VAC countries not up to the task IMO.

JR

Since this will be a USA experiment, I'm not worrying about 240-volts AC right now. If this works as envisioned, then a different design will be needed for the UK.

[Mike Sokol]

BTW  300VAC, 1250VDC and only $0.97 for onsey/twosey.

Hey, only 31 cents each in 5K quantities. I'm going to order of bag of these for my experiments.

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