I want to give my aging ST35 a tuneup

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I want to give my aging ST35 a tuneup

Postby Lafish » Thu Apr 20, 2017 2:10 pm

I built one of Shannon's earliest offerings, circa 2002, and it has served me well all these years. I used Hammond transformers and stuck to the parts on the BOM, only change was some hand-picked tubes from Roger Modjeski and those are probably at least 10 years old now too. It was always a bit noisy, mostly 60 cycles, and I could never chase that down. In a living room system it didn't really matter as it didn't intrude on listening. But I'm using the amp in my desktop system now, and it would really be nice to get it a bit quieter. Any thoughts on where to start? It still sounds great.
Larry Fisher
Port Townsend, WA
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Re: I want to give my aging ST35 a tuneup

Postby corndog71 » Thu Apr 20, 2017 2:20 pm

That noise could be a lot of things. Are your signal cables kept away from power cables? Are your signal cables shielded? Have you tried different tubes? Your driver tubes could be on their way out. It might be time to replace them. Do you use a preamp? When you say "desktop system" does that mean a computer? Computers can be noisy. Pay attention to where your electronics are. You may need to relocate the amp away from the computer.
some people call me Rob
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Re: I want to give my aging ST35 a tuneup

Postby paart » Fri Apr 21, 2017 9:22 pm

The very first thing to do is isolate the source of hum or noise. With everything un-powered, remove the input cables, and replace them with "shorting" RCA plugs. These are simply RCA jacks with the center pin and ground jumpered and soldered together. Install these plugs, power up the amplifier, and listen to the speakers. It should be immediately apparent whether noise is coming from one side, both channels, or if the noise is absent.
If it is absent or greatly reduced, then the issue is in another piece of equipment.
Obviously, if it is unchanged, then the ST35 will need some troubleshooting.
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