Replace Bypass Cap?

[Monjul]

I have a 20 year old tube amp in which the manufacturer recommended replacing the .22uf 600v Kimber Kap which is across one of the two filter caps to reduce ripple, I assume. The tech recommended replacing this cap with a PIO cap to improve sonics. Correct me if I'm wrong, but I don't see where the cap type, especially in this circuit position, can change the sound of the amp provided that the original cap is doing it's job. What do you guys think?

The yellow cap in question appears in the right rear of the attached photo. (Additionally, why isn't there a cap on the left most filter cap? Is it because the filter caps are in parallel and therefore doesn't require a second bypass cap or was the manufacturer being frugle?)

Thanks in advance.

[Rod Coleman]

The .22 won't be doing anything about ripple - it's an HF snuffer. They should be good for 10K hours at least. Could ask Kimber about actual durability.

The big electrolytics are a different matter. Even good quality screw-terminal types will degrade over the years. My experience is that they start sounding stale and dull long before you can measure anything wrong with them (capacitance meter, ESR meter tests). 10 years is usually enough, perhaps a little more for the best sorts.

KEMET/BHC do good sounding screw-term lytics:

FEBG - Electrolytic Capacitors

[tympani1d]

Rubycon photo flash caps!!!! I see you've got them scattered around in there!
I always found they made a huge difference in taming power supply noise and attack (leading edge) transient response. Nicely done.
One well remembers a pair of ARC D-250's much hot rodded with scads of these sprinkled about............lightning transient response (the stock D-250 was not any slouch) but golly the inner voicing and sound stage imaging was extraordinary with the flash caps.
Though i have no idea what one would replace them with today as I doubt they are avail. anymore.
Anybody?

[Monjul]

Originally Posted by Rod Coleman

The .22 won't be doing anything about ripple - it's an HF snuffer. They should be good for 10K hours at least. Could ask Kimber about actual durability.

The big electrolytics are a different matter. Even good quality screw-terminal types will degrade over the years. My experience is that they start sounding stale and dull long before you can measure anything wrong with them (capacitance meter, ESR meter tests). 10 years is usually enough, perhaps a little more for the best sorts.

KEMET/BHC do good sounding screw-term lytics:

FEBG - Electrolytic Capacitors

Thanks for the response. should I add a .22 cap across the other filter cap also?

Re: the filter caps: so the fact that when I shut the amp off and the storage caps play solidly for about 20-30 seconds doesn't necessarily mean the caps aren't compromised from age and heat? I thought this was a good test of filter caps?

[tympani1d]

Originally Posted by Monjul

Thanks for the response. should I add a .22 cap across the other filter cap also?

Re: the filter caps: so the fact that when I shut the amp off and the storage caps play solidly for about 20-30 seconds doesn't necessarily mean the caps aren't compromised from age and heat? I thought this was a good test of filter caps?

Nope, they're just fine, at least for the present. I'd say plan budgeting to replace and sit back............... enjoy .

[Monjul]

Originally Posted by tympani1d

Rubycon photo flash caps!!!! I see you've got them scattered around in there!
I always found they made a huge difference in taming power supply noise and attack (leading edge) transient response. Nicely done.
One well remembers a pair of ARC D-250's much hot rodded with scads of these sprinkled about............lightning transient response (the stock D-250 was not any slouch) but golly the inner voicing and sound stage imaging was extraordinary with the flash caps.
Though i have no idea what one would replace them with today as I doubt they are avail. anymore.
Anybody?

Are you talking about the two light blue electros? I was just about to purchase either BG's or Elna Silmic's to replace them. So I guess I should keep them in there? Thanks.

[tympani1d]

Originally Posted by Monjul

Are you talking about the two light blue electros? I was just about to purchase either BG's or Elna Silmic's to replace them. So I guess I should keep them in there? Thanks.

Yes those are the critters!
Now this may, likely will, creatre a fire storm of debate, BUT yes I would just leave them alone. Elna's are always good though.

SY, kevinkr, wavebourn may have more erudition on these subjects, perhaps they will comment?????

[Rod Coleman]

IME, capacitance value retention does not mean that the sound quality is also retained. For instance, after 20 years, even mid-to-low-level solid state guitar amps show a marked improvement if you recap them. In old caps I have removed, I have rarely measured any cap loss or ESR increase, even when the amp really performed better.

It doesn't call for any expertise to find out, since the Rubycons look like small sizes. Take them out carefully, so you can put them back if preferred (mark the polarity!!). Get some Nichicon VX or VR series (known-good garden variety 'lytics) and try them instead. If the sound improves, you know you need new caps, and can look out the Elna catalogue; if not you only spent a little beer money finding out.

Same with the Kimbers. Try the PC/HV/S made by LCR - it's a proper ultra-low loss industrial FKP that can embarass many a boutique cap. For coupling or decoupling.

from Farnell/Newark. A budget part that really performs.

LCR COMPONENTS|PC/HV/S/WF 220NF 1KV|CAPACITOR, 220NF, 1000V | Farnell United Kingdom

[kevinkr]

Not sure whether or not those little blue critters are in fact photoflash caps, but if they are read on..

Long ago I had a couple of those Rubycon photoflash caps burst into flames for no apparent reason other than that they have 0 ripple tolerance and are not suitable for continuous use in even moderately warm temperatures or IMNSHO any other situation. They do have very low ESL/ESR which is the one thing that makes them pretty ideal from a very limited perspective for audio applications. I learned the hard way, but was at least aware of the risk - and I never used them in anything sold to a customer.

My perspective is that this fad originated long ago with someone who was all too willing to ignore manufacturer applications information and part specifications and who got away with it. Like many things in high end audio that doesn't necessarily make it a good idea. There are or have been in the past a fair number of incompetents designing audio gear unfortunately.

Given their advanced old age I would consider these as candidates for immediate replacement. You might or might not have any issue, but when they burn they are just a little difficult to extinguish and make a lot of smoke.

[pauldune]

Maybe it was already clear from the other posts, but you dont need to bypass the other cap. The powersupply is directly in your signal path; the signal goes from the output transformer primary to ground. It tries to take the least resistance/shortest way to ground, which is normally the last cap in the powersupply. If you bypass that with a better quality (film or pio) cap, that will be the shortest way. Especially for high frequencies recommended. If there's a big choke between both caps, that will work as a blocker for higher frequencies. So the second cap doesnt see much signal or higher frequencies. No need to bypass it.

gr. Paul