...And yet another ST-70 is up and running!

Hello all, another new member to the forum. I've just completed Bob's ST-70 kit (with tubes and the PS/Russian PIO cap upgrade), and I felt it was worth a few comments.

Everything about this kit is first class. Shipping was fast and the packaging was excellent; I'm confident that box could have been dropped from a third-story window with minimal damage. I've never, ever spent an entire half-hour unpacking anything I received by mail or UPS - until last week.

Construction went without a hitch, and the amp worked flawlessly on initial power-up. My secret was to work slowly and check all connections before going on to the next step.

A couple of tips for anyone interested:

1. Installing the slide switches and power takeoff sockets in the chassis can be a real bear on a stock build, and those PIO caps really eat up any room you may have otherwise had to swing tools. I solved this problem by actually soldering the kep nuts to the flanges on each switch and socket, in effect re-creating the threaded holes in the original Dynaco switches (and described in the instructions). Use fine sandpaper to clean the surfaces to be joined, apply a little extra rosin flux, and use a HOT iron to flow the solder onto the lockwasher portion of each kep nut - and voila! Please note I did not do this for the power switch or the regular tube sockets.
   
   
2. The extra unused lugs on those power takeoff sockets really gave me the willies. I had visions of these things rubbing up against the PIO caps and causing all kinds of mischief, so I removed them completely. This can be done without any harm by depressing the little barb on the back side of each lug, then pushing the lug out of the tube side of the socket. If you're an experimenter like I am you may want to store the unused lugs in a small ziplock bag for future use; they can easily be reinstalled at a future date if desired.

Oh, and I almost forgot: this amp kicks a$$!! Someone in this forum said Klipsch speakers and the ST-70 were meant to be together, and I couldn't agree more. My '70 is pushing a pair of RF-3's (98 dB/1W/1m) and they sound fantastic, to say the least. Signal source is a lowly mid-90's vintage Sony Discman.

I've listened to this setup for two days now, and it hasn't failed to take anything I've thrown at it: Steely Dan, Handel, Bach, Count Basie, Joaquin Roderigo, and even Nickelback(!?). To steal a line from Blazing Saddles, "Mongo impressed!"

Thanks Bob!

I started doing that also about three years ago when I kept dropping the nut. It just occurred to me, screw it, why not just solder em on and be done with it right LOL. I do it by first using some 000 pad to just shine it up a tad, then put on the nut and screw finger tight and solder the nut onto the flange. I back out the screw then mount into the chassis with no problems at all now. A breeze to take off and put back on at my whim now. I make this a habit whenever I work on anything these days, as the older I get the harder it seems to hold those little nuts in place.

wolverine

I know what you mean, Wolverine (hey - that rhymes!). I got the idea of doing that when I built an Elecraft K2 transceiver, which is a MUCH more complex build than the ST-70 by far. I usually go inside my builds at some point in the future, and you're right about it helping with reassembly.

I do offer one word of caution: please be careful using steel wool around any electronics. That stuff sheds something fierce, and it could lead to some serious fireworks with high-voltage equipment. Don't ask me how I know...

Learned a long time ago the dangers of "tin whiskers". Only takes once and you learn real quick to clean up well, and in fact I vacuum using my shop vac which is really a sucker LOL. I always check traces, etc. and clean up the boards.

I should have mentioned that whenever possible I remove parts from the chassis to affix the nuts. I like this handy second set of hands I have that really holds things well for me. Clamps firm and is heavy so it's a breeze to solder on nuts to parts.

I re-capped a Pioneer SM-83 last year, replaced some out of spec resistors, no heavy surgery really, but a lot more difficult to work on an integrated as opposed to a Dynaco. One of my favorite parts of owning ST-70's is how easy it is to work on em.
wolverine

Oh yeah, the Klipsch speakers. I use a set of KG-4's on one amp, and on another I use an old birch set of Heresey's. I like the Heresey's best. Those speakers are the best set I've ever used on a low power tube amp. KG-4's are great mind you, but the Heresey's have this warm sound that is just so unique to them.
wolverine