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Old 2nd March 2008, 07:42 AM   #1
diyAudio Member
 
Join Date: Jan 2007
Location: The 1st State
Talking Modded ST70 Done

Gents,
Here's my take on a ST70:

Click the image to open in full size.
Click the image to open in full size.

And some quick guts shots:
Click the image to open in full size.
Click the image to open in full size.
Click the image to open in full size.

Details:
DIYTube Driver Board
Edcor 4.2k Outputs
PA-060S Power Tranny
SDS Cap Board
Dual Hammond 159v Chokes (Run in Series - needed the current rating)
Winged 'C' KT88's
RCA 12BH7s
Phillips 5751
Triode Mode Switch
Tiger Maple Base finished with water based dye and button shellac

Just a note on the Edcor's - They are 180' out of phase of the old Dynacos, you will oscillate if hooked up like the old dynaco's were :nono:
I just have it breaking in right now; so I won't comment on sound. It really does sound sweeeeeet though

-Steve
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Old 2nd March 2008, 12:16 PM   #2
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Join Date: Nov 2002
Are you sure your problem wasn't because your red and yellow wires need to be swapped? If hooked up correctly you wouldn't have had to be 180 off on the transformers.

Your using a switch to switch to triode mode? I thought that was a big no no because that switch is only rated to 250 volts.

What are the output transformers rated for in output? Looks like the big replacement power transformer too.

In all a nice job!!! Love the wood chassis too.
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Old 2nd March 2008, 02:20 PM   #3
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Join Date: Aug 2006
Nice job on the finish, Steve. Might just be the picture, but the lead on that Mojotone cap looks a little close to its body for my comfort. I would think you'd be ok with the triode switch provided you're only switching it with the power off.
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Old 2nd March 2008, 03:23 PM   #4
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Join Date: Jan 2007
Location: The 1st State
Guys,
The board itself is out of phase; so 'usually' you need to criss-cross like that. I in fact needed to go back and uncross them.
Triode mode switches rated for 330vac will be fine - just ALWAYS only do it once the amp is off.
The OPT's are rated for 60w, and the PT is the Triode electronics replacement (good for 300mA I believe).
On the driver board - I did go back and shrink wrap the leads on the caps. They didn't look that bad until I took that photo


Thanks for the kind words !
Steve
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Old 3rd March 2008, 11:12 AM   #5
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Join Date: Nov 2002
Does your PA-060S have filament windings?
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Old 3rd March 2008, 01:34 PM   #6
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Join Date: Jan 2007
Location: The 1st State
Yes - here's the specs:

http://store.triodestore.com/mq060.html
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