I'm new here, and from England, so apologies if my language is sometimes incomprehensible. I'll do my best to remember "tube" and "wrench" and the fact that the metric system may not be everyone's first choice
I'm also new to Dynaco, as of yesterday, when I finally got hold of an ST-70. Sadly they're not so common over here, so I've had to wait a while, nor are they as cheap as in the US I'm afraid. But now I have one, and having made up some speaker leads I spent the rest of yesterday listening to it. It's a peach ! So now I'm ready to see what I can find out about it.
It seems to be factory wired. At least, it's got the rivets and the label. But it doesn't have the "spanner screw" - in fact it's only got two screws each side. And the 1k grid-stopper resistors are wired onto the tube bases, not direct to the PC board. I can't see any sign of a factory inspection stamp either. Strangest of all is that the PC board appears to be contemporary with the rest of the amp, but it is green (fiber glass ?) with the legend STEREO PC3 in one corner. Was this kind of board ever used by Dynaco or is it a more recent replacement ? And is the general opinion that this really is a factory wired amp ?
I'd also be interested to know what date it is. The electrolytic capacitors are no help - they've been renewed. The serial number is 6410912. I read in another thread that Dynaco's serial number records no longer exist. But maybe there are forum members who know both the date and the serial number of their amps and who might at least set some limits on which ones were made when ? I also read that the bias pots can be dated. I can't see anything which looks obviously like a date on mine. But they have the numbers 1376402, and EQ9373 stamped into the underside as well as the 10k resistance value. Is the date in there somewhere ?
In general I think the amp is in quite good condition. There are some blemishes (scratches, small rust spots etc in the chrome, a few scrapes on the cage paint, some lettering missing). But it's probably not much younger than I am and I'm not scratch-free either ... If I could change one thing I would quieten the mains transformer. It buzzes significantly and the cage and chassis seem to resonate and amplify this. Of course the AC supply runs at 50Hz here so it may be that I will see different problems from the ones you're used to. I think I will try the anti-vibration isolators first. They're not expensive and I can take them out again if they don't work. I have to say I'm tempted by a replacement transformer. This should both fix the hum and also let me wire the primaries for 240V which would mean I could dispense with the step-down transformer I'm currently using. On the other hand a new transformer won't be cheap (I've got transatlantic shipping as well as import duty on top of the base price). And some part of me really doesn't want to mess with what might be a fairly untouched unit. So I think I'll wait a while and see what the isolators do.
OK, enough for now. I've attached a few pictures to show what I've been talking about.
All the best,