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FDP Forum / Fender Amps: Vintage (before 1985) / Cost of a DIY Cap Job?



Apr 7th, 2012 08:09 PM   Edit   Profile   Print Topic   Search Topic

If I wanted to replace all the caps in my '72 SFDR, how much money could i expect to spend on parts if I did it myself?

Also, I've been reading and researching amp maintenance for years and terms and phrases like "coupling caps", "bypass caps", "tone stack", "cathode", and "filters" are still very vague to me. I've never seen a picture where these things are clearly labeled. If they're identified at all the image is usally a pic of the insides of a chassis and I can't tell one thing from another (for the most part).

I've done a few minor repairs amps and guitars...i know what a pot is and how to solder, etc., but if someone could point me to some books or sites with clear pictures that identify these things i'd appreciate it.


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Apr 8th, 2012 08:18 PM   Edit   Profile   Print Topic   Search Topic

EL34 World and Hoffman Amps website has good info. The left picture in the link below probably shows Deluxe Reverb filter caps under the "doghouse" (the metal cover behind the tubes). There are other links on the site that will also show the bypass caps and bias cap which are commonly replaced due to age. Be forewarned that there is significant voltage stored in filter caps and you must discharge them so as not to get shocked.

Filter Caps



Apr 8th, 2012 09:38 PM   Edit   Profile   Print Topic   Search Topic

A wholesale replacement of caps would be under $100, and about 1/2 that if you just replace the electrolytics (bypass, bias, and filter caps). If you haven't done a lot of work on amps, it's a good idea to test new parts before you solder them in, and check the amp as you go.



Apr 8th, 2012 11:57 PM   Edit   Profile   Print Topic   Search Topic

Mm... I like Sprague Atoms for the filter caps and the cathode caps. They're expensive but they're worth it. Filter caps run about 10 dollars each and cathode caps are about a buck apiece, so that would bring the parts cost for a complete cap job up to just under a hundred bucks. On the other hand, you can expect not to have to do another cap job for the next twenty years. Works for me. :)

tubesandmore.com is pretty much one-stop shopping for Sprague Atoms, they're very fast and everything's in stock and I've always had good experiences with them.

Let's see, I wouldn't bother replacing any of the coupling caps, those things almost never go bad and the original ones have the original tonal quality, so unless there's a specific reason to I wouldn't touch those. Filter caps, on the other hand, don't affect tone (much), and they're more an issue of electrical safety and reliability. Cathode caps are kind of in between, they do affect tone but in Fender amps the knee sits around 50 Hz (well below low E on a guitar) so any old 25 uF cap will probably work and sound acceptable, and in this case the reason I like the Spragues is more for longevity and reliability.

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Apr 9th, 2012 08:10 AM   Edit   Profile   Print Topic   Search Topic

When teaching novice folks about amp service and electronics in general, I tend to refer to the caps in a guitar amp by what they "are" versus what they "do". That is, electrolytic caps should be replaced periodically while the ceramics, polys,micas and such don't unless they are proven to be defective and causative of a problem. This takes away the immediate need to differintiate terms like "filters", "bypass cap", "Cathode cap","coupling cap", etc, etc, etc. Then it only becomes necessary to be able to identify the different types of capacitors by appearance which is pretty simple.


(This message was last edited by willie at 08:12 AM, Apr 9th, 2012)

FDP Forum / Fender Amps: Vintage (before 1985) / Cost of a DIY Cap Job?

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