My First ST-70

knowledge base for the classic Dynaco ST70

My First ST-70

Postby rockable » Sun Apr 13, 2008 4:01 pm

Did I do ok? I decided to buy this one and take a chance on the tubes. If they're good, I did pretty well. If not, I did ok.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=160229480437&ssPageName=STRK:MEWN:IT&ih=006
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Postby Ty_Bower » Sun Apr 13, 2008 6:57 pm

It looks like a fine amp. The chassis appears especially clean. Be sure to check the caps carefully for leakage, and replace the selenium diode in the bias supply.
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Postby rockable » Sun Apr 13, 2008 7:16 pm

Replacing the caps and power cord will be first order of business.

Do most of you go with the 40/80/30/20 cap can or with one of the custom boards?

How's the reliability on the cap cans? I've used quite a few on Fender amps and never had any problems but I realize that's a different animal.
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Postby SDS-PAGE » Sun Apr 13, 2008 7:17 pm

Looks good. You win as long as the irons and chassis are in good shape. Tubes and other stuff can easily be replaced fairly cheaply.

You might want to consider using a SDS cap board. Some folks here seem to have problems with replacement can caps. Mine's original and it's working fine.
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Postby Ty_Bower » Sun Apr 13, 2008 7:22 pm

I've heard as much bad about the cap cans as good. You'll fare a little better with the cap cans for the ST70. Forget about buying replacement cans for a MkIII.

I probably wouldn't jump straight into replacing the can until I knew it was bad. Whatever route you take, replacing it is going to cost you $70 or so. If it does need replacement, I'd go with the cap boards rather than a new can.
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Postby rockable » Mon Apr 14, 2008 11:27 am

I have a capacitance meter, so I'll check it for capacitance and visually inspect it for leakage. If there is none, I may Rock On!

Changing the power cord to a 3 prong is a good idea, tough. Right?
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Postby burnedfingers » Thu Apr 17, 2008 5:18 am

I would suggest using the cap board. I have used the can in the past and have not had 100% success rate with it. The board offers you the ability to replace the caps in the individual sections as needed over time at a cost savings.
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Postby EWBrown » Thu Apr 17, 2008 9:14 am

You can use a three line power cord, black (or brown) is "Line", white or blue is "Neutral" and green or green/yellow is the safety ground, which can connect to the chassiis - use a ring lug and fasten to one of the power trannie mounting screws.

If you develop a ground loop hum problem, after trying a 3 wire cord - it does sometimes happen - then just disconnect the green wire, and tape up the loose end.

/ed B
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Postby rockable » Thu Apr 17, 2008 10:40 am

That's the way I wire them in Fender amps, EW. Do most of you use 2 line or 3? I just felt 3 was safer, although it's not quite the same risk of shock as a guitar amp.
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Postby Slartibartfast » Thu Apr 17, 2008 10:51 am

rockable wrote:That's the way I wire them in Fender amps, EW. Do most of you use 2 line or 3? I just felt 3 was safer, although it's not quite the same risk of shock as a guitar amp.


I use 2 wire cords on all my stuff. I do it to avoid any ground loops.
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Postby EWBrown » Thu Apr 17, 2008 11:12 am

I've used both 2 line and 3 line cords, just depends on what I have handy in the junk box... My simple rule of thumb is lower powered (18 WPC or less I use 2 wire, for the big stuff, 35WPC and up I use 3 wires. but not always...

As they say, six of one, andhalf a dozen of the other.

Not the same shock hazards as a guitar amp, just ask Keith Ruchards, he experienced that kind of shocking event at least once in the 60s or 70s... :o

And over in the UK, he had 240VAC, and the amp was hot and the mic stand was not, and he had 240VAC from fingers on both hands to his lips. :o

Bzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzttttttttttttttttttttttttttttt!!!!!!!!!!!!!! at 50 cycles per second.

I'd bet that left a funny taste in his mouth for a long time..... Yellow_Light_Colorz_PDT_21

/ed B
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test!

Postby traveler2000 » Mon Sep 01, 2008 3:32 am

that's ok!
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