What is the difference between these caps

[corduroyew]

I'm need to recap my amp and can't find affordable Polypropylene Capacitors in some of the values I need. I can find metallized Polypropylene capacitors in the right values. Will they work? Or will they sound horrible? I want to recap the amp with vitamin Q caps in the next year or two but I need something that will help the amp sound better now. Waiting and saving money isn't an option. So will metallized poly caps sound ok on an amp?

[bob p]

I'm need to recap my amp and can't find affordable Polypropylene Capacitors in some of the values I need. I can find metallized Polypropylene capacitors in the right values. Will they work? Or will they sound horrible? I want to recap the amp with vitamin Q caps in the next year or two but I need something that will help the amp sound better now. Waiting and saving money isn't an option. So will metallized poly caps sound ok on an amp?

i wouldn't hesitate to use metallized caps in a guitar amp.

[Steve Conner]

I mostly just use the orange metallized polyester ones from Rapid Electronics:

http://www.rapidonline.com/productin...moduleno=62514

Are the existing plastic film caps in your amp actually starting to go leaky? To me, "Recap" means to change out the big electrolytic filter caps, when they start to go stale after 10-20 years. The plastic film type don't ever need replacing unless they are actually breaking down and making the amp malfunction.

[bob p]

i agree with Steve -- when i think of "recapping" an amp, I think of replacing electrolytic caps that are old, and any coupling caps that might prove to be causing trouble. electrolytics will wear out with age. most coupling caps are self-healing and rarely cause trouble. most of the time its not worth replacing them unless you just like to solder.

the only time that i've ever had a metallized or a film foil cap go bad was when it was subjected to mehanical trauma. in my case, it was on the crossover board in a set of very expensive HiFi speakers, where a plastic cable-tie had been used to hang a very heavy inductor on the bottom of the board. the cable tie went around the inductor, through the board, and around a PP film/foil cap. what a stupid idea. the weight of the inductor and the tension that it placed on the cap caused enough mechanical trauma to cause the cap to fail. its pretty rare to see film/foil or metallized caps fail otherwise.

id you've got a really old amp, you might run into paper in oil coupling caps that get leaky and need to be replaced, but a good film foil or metallized coupling cap should last a lifetime.

as far as selection goes, i base my selection on form factor and on price. for axial lead caps, i like the M150. for radial lead caps, i like the ODs though the Xicon caps can be found a bit cheaper. i think that just about everyone would agree that the VALUE of a coupling cap matters a lot more than its construction.

[corduroyew]

I mostly just use the orange metallized polyester ones from Rapid Electronics:

http://www.rapidonline.com/productin...moduleno=62514

Are the existing plastic film caps in your amp actually starting to go leaky? To me, "Recap" means to change out the big electrolytic filter caps, when they start to go stale after 10-20 years. The plastic film type don't ever need replacing unless they are actually breaking down and making the amp malfunction.

Yes, I've tested the plastic film caps (if thats what they are) and a few of them have started to go leaky. While I'm at it I decided to replace the electrolytic filter caps too. My amp is a 1966 ab165 bassman. I've got 3 problems with it. The first is hum, second is that it starts to break up at about 2.5 and the last problem is that when it does start to break up it gets fizzy and crackles like there is a short in my lead or something but then when I realy drive it, it sound ok most of the time. I don't know if replacing the caps will fix any of these things, but I do know the caps need replaced and I'm sure I can handle doing it once I find the parts so I figure I'll go for it and then see what happens.

[Marc]

don't forget the resistors!

Double check those carbon comp resitors, if you haven't already. If they're much more than 10% out of tolerance suspect them as contributors to you problem sounds.

Personally, I'd replace them if they were even 10% out. That's a bit fussy but I've found so many CC's that were noisy, especially plate load resistors, that I have found it easier to simply take them out even if it turns out that they weren't the problem afterall. Unless of course my customer simply must have them.....then there's always the Xicon replacements.

Marc

[corduroyew]

^Swaping the caps helped but it didn't fix everything so I did what you said and checked all the resistors. Not only did I find that some of them were off by as much as 30%, but I found that it was missing a couple resistors too. It sounds a lot better now. Thanks for the help.

[soundmasterg]

A 1966 ab165 bassman hmm?

It probably had the blue "molded" mallory coupling caps in it right? Those rarely go bad, and sound very nice. I would have only replaced the ones that were bad myself, and would have used polyester replacements instead of polypropylene, but each to his own. Those blue molded ones were polyester and go for high dollars online from some vendors.

Greg

[corduroyew]

A 1966 ab165 bassman hmm?

It probably had the blue "molded" mallory coupling caps in it right? Those rarely go bad, and sound very nice. I would have only replaced the ones that were bad myself, and would have used polyester replacements instead of polypropylene, but each to his own. Those blue molded ones were polyester and go for high dollars online from some vendors.

Greg

Those are the caps that were in the amp and I had 4 of them that were bad. I keped the ones in there that were good and I also stole the one that was on the ground switch and used that to replace one of the leaky caps. So I replaced I actualy only put 3 of the polypropylene caps in the amp. So you think I would be better off taking out the polypropylene and putting in polyester?