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ST-70 back in service


Marvel

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Phew! Finally got the new EL34s. Biased fine and sounds sweet, right off the bat. The new, heavier power transformer from Ned helps a lot. After a couple of hours, I can keep my hand on it with no problem at all. It is quite warm, but not hot like the original. Makes the Heresys sound so good.

As soon as I get the film processed, I'll post pics of the work. All that is left of the original amp is.. the input jacks and output terminals. I'll get around to those one of these days.

Marvel

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Suggestion that works

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A power supply upgrade/update that includes removal of the power tranformer should include transformer to chassis isolation. Go to Home Depot or Lowes and purchse some rubber faucet washers (FW) and some plated metal washers (MW), and slide them onto transformer bolts. The sequence is BOTTOM OF TRANSFORMER/MW/FW/MW/Chassis/MW/FW/MW/NUT. You will help eliminate the 60hz vibration and improve the noise level of that ST70. Not a bad thing to do on any amplifier.

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The original power transformer did not have any vibration either, but it ran way too hot. The new one does get hot, but not excessively so.

Other than new binding posts and input jacks, I will probably let this project rest awhile. Now it is at the point where I can enjoy it without thinking it will burst into flames.

THe new project should be a tube pre, and I don't know if I want to build from scratch or buy one. I have other plans for money (building some speaker cabs). I am using a commercial (Biamp Advantage SPM412e) SS preamp with it right now, and it works fine. Not as good as I would expect even from my budget, but it is okay.

Marvel

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Biamp is still in business, and is affiliated with Rauland-Borg. They do a lot of contractor equipment. Actually made in the USA (with a price to match). We were getting rid of this at work, and I am like fini. Things end up in my car instead of the dumpster. Eventually they end up being used or finally make the final trip to the landfill.

This audio preamp ties together with a video switcher as well, although it only handles composite video.

Marvel

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