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My dead Dynaco ST-70
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Author:  Guy [ July 31st, 2013, 8:25 pm ]
Post subject:  Re: My dead Dynaco ST-70
Good point, Dave, I forgot that!
Author:  craigh [ August 1st, 2013, 4:35 pm ]
Post subject:  Re: My dead Dynaco ST-70
Ok, I pulled her out from her hiding spot. The fuse seems to be ok. She was sitting in a garage for about 4 years after she died & today I cleaned 30 years of dirt. Still have another 25 years of cleaning to do. This was a factory built unit in Philadelphia & shows a postal zone.

Craig
Author:  craigh [ September 9th, 2013, 5:30 pm ]
Post subject:  Re: My dead Dynaco ST-70
Update.......
Thanks to David Berning, I replaced the surge voltage capacitor & of course the fuse. I ordered the wrong rectifier tube. Ordered a 5Y3S instead of a 5AR4. So I tried it with the old 5AR4 & the same thing happened. What would happen if I used the 5Y3S? One of these days, I'll get the correct tube. Naturally my guitar amps use a different rectifier tube.

Craig
Author:  dberning [ September 16th, 2013, 10:37 am ]
Post subject:  Re: My dead Dynaco ST-70
Craig,

Recall that your 5AR4 was shorted. You need to get a new one. When your brought the amp over I put a 5U4 in for testing. You can use a 5U4, you would just have a little less power. The 5Y3 can not handle the current required by the Stereo 70.

David
Author:  Roscoe Primrose [ September 16th, 2013, 11:22 am ]
Post subject:  Re: My dead Dynaco ST-70
dberning wrote:
Craig,

Recall that your 5AR4 was shorted. You need to get a new one. When your brought the amp over I put a 5U4 in for testing. You can use a 5U4, you would just have a little less power. The 5Y3 can not handle the current required by the Stereo 70.

David


I'd be careful using the 5U4 in that amp. The 5U4 requires 5V/3A for the filament, whereas the 5AR4 only requires 5V/2A. I don't think the ST70 power transformer is known for being over-engineered ;) A 5R4 might be a better substitute.

Roscoe
Author:  craigh [ September 16th, 2013, 12:00 pm ]
Post subject:  Re: My dead Dynaco ST-70
A new 5AR4 should be coming in today's mail.

Craig
Author:  Guy [ September 16th, 2013, 3:03 pm ]
Post subject:  Re: My dead Dynaco ST-70
Bien, progress! :mrgreen:
Author:  randy warren [ September 16th, 2013, 8:30 pm ]
Post subject:  Re: My dead Dynaco ST-70
if you haven't done a cap job, your just asking for trouble, those filter caps in the dunaco were run to the limit, and after setting for so long, got to be bad. Not sure of your electronics experience but I am guessing it's limited, and there are procedures used to bring an old sitting piece of gear up to a usable and safe level, need to get with those...
Author:  craigh [ September 17th, 2013, 11:29 am ]
Post subject:  Re: My dead Dynaco ST-70
I got the correct tube in now. (I never put the wrong tube in there). Turned it on. Everything glows properly & no sound. Put my old solid state amp in & everything works. What now? Give it up? Any ideas?

Craig
Author:  randy warren [ September 17th, 2013, 11:44 am ]
Post subject:  Re: My dead Dynaco ST-70
sounds like you need to take it to a technician, although you did indicate that David worked on this with you, so that should have done the job. Perhaps when you plugged in either the wrong rectifier or the shorted one you f'ed it up...
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