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Author
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Topic: Syptoms of bad Filter Caps
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Lefty
Member From: Grayson, Ga.
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posted 07 August 2003 08:55 AM
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I was wondering if old filter caps show any syptoms before complete failure? Do they show power loss, or noise, etc. I carried my 1966 Fender Bandmaster in for service, and was told the filter caps were fine.
I also have a 1957 Fender Pro with all original parts that sounds fine.
Is there any merit to changing them before failure (excluding the obvious inconvienence)?
I recently bought a 1984 Boogie, and am pondering changing the filter caps.
Thanks,
Lefty
Sho-Bud LDG
Dekley D-10 (soon)
Session 500
rickenbacker lap |
Brad Sarno
Member From: St. Louis, MO USA
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posted 07 August 2003 11:55 AM
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Change the cap's! No good reason to let the power supply go bad. There is merit in keeping the old signal cap's because they strongly effect the tone. Filter cap's serve a different purpose. Early symptoms are the sound of 60Hz hum in the audio. If they go bad or begin to leak DC, things can start to get ugly. Tubes love clean power supplies. ------------------
Brad Sarno
Blue Jade Audio Mastering
St. Louis |
Gino Iorfida
Member From: Oakdale, Pennsylvania, USA
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posted 07 August 2003 12:30 PM
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Filter caps will sometimes show physical signs of wearing, such as bubbling etc.
The 60hz hum may or may not appear until they are REALLY bad etc. Another sign is if you run the am hot enough to overdrive the output, you'll hear a low following 'ghost tone' over the fundamental note (think ring modulator effect!)-- most pronounced on higher strings. --personally, I would NOT run an amp of this age that hot to even see if they are bad. I'd just go ahead and change them.
However, remember electro caps were meant to last 5-10 years max. Seeing that your amp is nearly 50 years old, and the caps are original, it's not a matter of IF they fail, but WHEN they fail. New caps installed will run you way under $100 (in a lot of cases half that, and if you can do it yoruself, under $20). Cheap insurance policy. when a cap fails, it can and most likely will take out your rectifier tube (NOS 5ar4/gz34 tubes are NOT cheap!), and also possible is damage to any of the transformers in the amp. When these caps fail, they go to a true short, that can easily burn the power transformer, output transformer and choke (if the amp uses a choke). Changing these caps will NOT devalue the amp, in fact, save the old caps, and if you would sell them with the amp for nostalgia purposes some guys like that... more importantly, if you have to replace an transformer, you will watch the value of the amp fall through the floor, not to mention, the tone of the amp will NEVER be the same with new transformers. Filter caps will not kill the tone, but rather make the amp quieter and make the amp sound as it should. |
Terry Downs
Member From: Garland, TX US
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posted 09 August 2003 10:40 AM
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I just sold a 69 Fender Bassman amp head on Ebay for $355. I've been watching them for some time before I arrived on the starting bid. It appears there is value added when the old tube amp has new power supply filter electrolytics and a conversion to a 3 prong power cord (which I did on this one). Electrolytics are a wear out item like the belts and hoses on our cars. You can ignore it and let it leave you stranded unexpectedly, or you can preemtively maintain it. Here is a source I have used:
http://vibroworld.com/parts/tech15.html#caps Regards,
Terry |
Bob Metzger
Member From: Waltham (Boston), MA, USA
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posted 09 August 2003 02:10 PM
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I wouldn't let filter caps (and all electrolytics, for that matter) have a service life longer than 20 years in a tube amp, especially more so for steel guitar usage. These caps have a number of symptoms they exhibit when nearing the end of their service life but new caps will make an amp alot stronger and more solid sounding. For blues/rock guys looking for tons of sag, it could be a different story. I've seen a few guys unhappy tonally with the resullts of a re-cap but not people who are after a strong, clear, clean sound. |
Gino Iorfida
Member From: Oakdale, Pennsylvania, USA
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posted 09 August 2003 06:32 PM
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I've heard a lot less guys unhappy with the tone after a recap than I've heard unhappy guys after having to spend a few hundred $$ on replacement transformers after neglecting a recap. ... the way I see it, the tonal change from a recap will be MUCH less than new transformers...I agree, that 20years is really pushing things, esp. when caps were only ever supposed to last an average of 5 years, 10years max.[This message was edited by Gino Iorfida on 09 August 2003 at 06:34 PM.] |
Bob Metzger
Member From: Waltham (Boston), MA, USA
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posted 10 August 2003 11:50 AM
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Most filter cap manufacturers recommend a service life 8~12 years for commonly used elecytolytics. I find that in tube guitar type amps that you can usually get more years out of most caps, depending...Certainly, the vast majority of users who replace filter and other caps are completely pleased with the results. I was merely pointing out that it is not always universal. And to answer Lefty's question, yes, I agree with Gino, there's great merit to replacing filter caps before failure; you don't want a catastrophic failure to stress out all your amps components or cause downstream failure of otherwise functioning parts. B.
[This message was edited by Bob Metzger on 11 August 2003 at 01:10 PM.] |
Lefty
Member From: Grayson, Ga.
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posted 11 August 2003 05:32 PM
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Thanks to everyone for the good information.
I am in the process of sourcing the caps for several amps.
Thanks,
Lefty |
Ken Fox
Member From: Ray City, GA USA
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posted 11 August 2003 06:15 PM
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You will get excellent pricing on caps at Mouser Electronics. | |
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