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Bringing a flood-damaged ST-70 back to life

arts said:
That looks pretty good, just like new. Was the unit actually submerged in the flood?
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I don't know the extent or duration of its exposure, but the silt/debris in the original post pics was definitely from rising water. I woke up at 2am to 2.5 feet of water in my loft near downtown Dallas. It was my sixth day there. Totaled my car, lost guitars, an electric piano, all of my vinyl. Brutal.
 
ADClosson said:
I don't know the extent or duration of its exposure, but the silt/debris in the original post pics was definitely from rising water. I woke up at 2am to 2.5 feet of water in my loft near downtown Dallas. It was my sixth day there. Totaled my car, lost guitars, an electric piano, all of my vinyl. Brutal.
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Very sorry to hear about your flooding. One concern could be the bias pots holding some water, you may want to flush them out with very high % rubbing alcohol and perhaps Deoxit. Look for any chambers/areas like the bias pots, choke and fuse holder that could possibly hold water. But as others have said and looking at the pics, I think you'll be in great shape.
 
Inclined to agree with the suggestion of a slow bake just to be 100% sure. Maybe with the end bells removed to allow for better moisture escape. If the oven will run under 200 degrees, thats perfect. Even better if it has a convection fan. Just turn it on for an hour or something and let it sit there and cool off slowly. If the bias pots are at all flaky after cleaning, replace them. Also a good idea to run a 47k from the negative end of the pot to the wiper just as insurance. That way if the wiper loses contact for some reason, the tubes go full negative rather than to zero bias.

but I don't think you're going to have any serious problems here.
 
Floods are bad news. I once had only 6" of water back up in the basement. Had to rip out drywall, insulation, molding, baseboard heaters and carpet. I had LPs up on a wooden shelf/structure. The water actually wicked up the wood and got all the jackets wet. Had to spread them out all over the house to dry, plus wash all the records. The jackets were never quite the same, but the LPs survived OK. General rule in the basement now is anything important goes in plastic storage bins.
 
It totally sucks that the OP got flooded out. I've been evacuated twice since the early 80's. The town where I live now is in a bowl, levies completely surround it with two rivers that wrap around three sides.
Luckily my home was on a bit of high ground the first time and no damage.
The second time I was living a few miles out of town. Again, the levie broke somewhere else. There's nothing worse than having the police, or radio telling you to get out now, nother than losing everything.
 
I would take the flooded one and run the oven at 100 degrees for an 3 hr with the whole amp in there.
as far as the transformers one at a time take them out & sandblaster to it with the bells on then remove the bells and with a slightly oily rag and wipe the plates clean. while you have the bells off check out the electrical of the transformers with a multi meter to make sure they are not soaked inside of the plates. as far as the rest you can buy a new chassis, buy a new board. it would be a nice project .
 
So I finally got ahold of tubes and brought the amp up on a variac. The amp appears stable. After ten minutes of warm up, I tried to bias each side to 1.3 VDC. I could get the left side to sit at the appropriate reading, but the right side won't exceed .79 VDC despite being adjusted to the maximum setting. Any thoughts?
 
Weak tubes or something funny in the bias circuit causing the grid to be overly negative maybe. If swapping tubes doesn't do it, check the voltages on the sockets on the low channel. If its missing plate or screen supply to one socket that tube won't do anything. Grid volts you can compare side to side.
 
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