This is a pure analog amp from the 80s. Worked fine and had been continuously on for over 6 months.
Today I was sitting in the living room and heard an electrical like noise from the amp. Speakers were dead quiet. It was a very rapid mechanical ticking, arcing, electrical noise. It kept gradually getting louder.
I took the cover off to see what was happening. I couldn't pinpoint where the noise was coming from. At this point it was getting pretty loud, so I turned it off.
Any overall clues on what this may be, before I start tearing it apart? No burning smell. And nothing looks out of the ordinary visually.
Thanks for all of the help as always.
Today I was sitting in the living room and heard an electrical like noise from the amp. Speakers were dead quiet. It was a very rapid mechanical ticking, arcing, electrical noise. It kept gradually getting louder.
I took the cover off to see what was happening. I couldn't pinpoint where the noise was coming from. At this point it was getting pretty loud, so I turned it off.
Any overall clues on what this may be, before I start tearing it apart? No burning smell. And nothing looks out of the ordinary visually.
Thanks for all of the help as always.
Very likely it is an internal short in an electrolytic cap. these are aluminum bottles with water slime inside, sealed with rubber or something better. Usually rubber. They last from 1 to 25 years, unless sealed with epoxy (very rare) or a metal crimp (never since 1955)
You can test them, but if I have something audio I like, that sounds bad, and the calender says the production date was more than 15 years ago (or 3 years on computers or TV's) I change them all.
If you try it yourself, do two at a time. Amateurs make a lot of soldering errors, if you make one you and the sound gets worse, you know just where your mistake likely was. Buy them all at once though, shipping from real distributors is 2 to 100 times expensive as any cap.
I use the ones rated over 3000 hours service life, to avoid replacing them 4 times like I had to do in my 1961 build amp, using TV parts store quality caps. I use newark and digikey that have service life rating available in the selector table. Mouser sells some long life ones but makes you download the manufacturer's datasheet & read it. E-bay they might be old, the rubber deteriorates even sitting on the shelf unused.
Soldering tutorial is on jameco.com
Safety note: No work with plug in power socket. Check caps with DVM for voltage <1 before touching any internal metal. If not discharge with insulated tool shown in sticky thread of tube amp forum. Work one hand at a time touching amp, voltage that doesn't cross your heart won't stop it. Wear no jewelry, even low voltage through a ring or necklace can burn your flesh to charcoal. Wear safety glasses soldering: it can splash, especially desoldering. Liquid metal in the eye is not good for them.
That noise can also be a pitted or oxidized protection relay contact, or an ittermittant connection in a selector switch or mode switch, or short in an input cable. these require troubleshooting to find, unfortunately.
Best of luck.
You can test them, but if I have something audio I like, that sounds bad, and the calender says the production date was more than 15 years ago (or 3 years on computers or TV's) I change them all.
If you try it yourself, do two at a time. Amateurs make a lot of soldering errors, if you make one you and the sound gets worse, you know just where your mistake likely was. Buy them all at once though, shipping from real distributors is 2 to 100 times expensive as any cap.
I use the ones rated over 3000 hours service life, to avoid replacing them 4 times like I had to do in my 1961 build amp, using TV parts store quality caps. I use newark and digikey that have service life rating available in the selector table. Mouser sells some long life ones but makes you download the manufacturer's datasheet & read it. E-bay they might be old, the rubber deteriorates even sitting on the shelf unused.
Soldering tutorial is on jameco.com
Safety note: No work with plug in power socket. Check caps with DVM for voltage <1 before touching any internal metal. If not discharge with insulated tool shown in sticky thread of tube amp forum. Work one hand at a time touching amp, voltage that doesn't cross your heart won't stop it. Wear no jewelry, even low voltage through a ring or necklace can burn your flesh to charcoal. Wear safety glasses soldering: it can splash, especially desoldering. Liquid metal in the eye is not good for them.
That noise can also be a pitted or oxidized protection relay contact, or an ittermittant connection in a selector switch or mode switch, or short in an input cable. these require troubleshooting to find, unfortunately.
Best of luck.
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In these cases, a screwdriver is a great diagnostic tool. Kid you not. Put the blade on the mechanical thing that you suspect of making the noise, hold the end of the handle into one of your ears. Very revealing (mechanics used that in pre-computerized-cars times to diagnose engine sounds).
Does the music continue without interruption?
Jan
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