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[/img]2 posters
Latest Builds in wood; ST70, SP12 & SP14
gener8r- Posts : 61
Join date : 2012-04-28
howlin' hoosier- Posts : 38
Join date : 2012-04-30
What's going on under the hood of the ST-70?
gener8r- Posts : 61
Join date : 2012-04-28
Unfortunately I don't have a photo of the "upskirt" as I've built a number of ST70s.
Pretty much it's wiring follows just about any ST70 out there, as the original layout is close to perfect:
The Toroidal power tranny wires-up the same way as the original type.
There is now an IEC next to the fuse holder and the on/off switch has been moved to the front panel with a twisted pair. Grounding is completed back to the IEC, something I always thought was a shortcoming in the original Dynacos: a floating ground.
I deliberately chose not to add the pentode/triode switching; I can't hear much difference, the folks I build for won't know or miss the difference, and it allows more of the natural wood to show on top, which is what this set is all about.
This has the 12AU7 version of the driver board with all components mounted on the bottom except the tube sockets and bias pots. This allows the board to be mounted with just the tubes protruding, which to me looks a whole lot better than having an open/stuffed PCB staring back at you as with the original casings. The four red test jacks and the one black jack behind the center tube are the test points for biasing, paralell to the corresponding trimmer. Again,a nd in my mind this looks a whole lot better than the two tube sockets on the front panel, and the test jacks make checking the bias so much easier.
I am now building another ST70 with the new octal 6SN7 driver board just to try it and to go with/match the SP14 that's shown.
Modern ST70s, especially with these particular tubes4hifi driver boards, are world class sounding amps. I got started down this road with a kit from Bob. I've always maintained they are the best "bang for the buck" in all of audio. The only thing that holds them back IMO is their appearance, which in my mind I have rectified to my liking. The friend I built this one for has had a few of his friends implore him to ask me to build sets for them. If I only had the time.
Pretty much it's wiring follows just about any ST70 out there, as the original layout is close to perfect:
The Toroidal power tranny wires-up the same way as the original type.
There is now an IEC next to the fuse holder and the on/off switch has been moved to the front panel with a twisted pair. Grounding is completed back to the IEC, something I always thought was a shortcoming in the original Dynacos: a floating ground.
I deliberately chose not to add the pentode/triode switching; I can't hear much difference, the folks I build for won't know or miss the difference, and it allows more of the natural wood to show on top, which is what this set is all about.
This has the 12AU7 version of the driver board with all components mounted on the bottom except the tube sockets and bias pots. This allows the board to be mounted with just the tubes protruding, which to me looks a whole lot better than having an open/stuffed PCB staring back at you as with the original casings. The four red test jacks and the one black jack behind the center tube are the test points for biasing, paralell to the corresponding trimmer. Again,a nd in my mind this looks a whole lot better than the two tube sockets on the front panel, and the test jacks make checking the bias so much easier.
I am now building another ST70 with the new octal 6SN7 driver board just to try it and to go with/match the SP14 that's shown.
Modern ST70s, especially with these particular tubes4hifi driver boards, are world class sounding amps. I got started down this road with a kit from Bob. I've always maintained they are the best "bang for the buck" in all of audio. The only thing that holds them back IMO is their appearance, which in my mind I have rectified to my liking. The friend I built this one for has had a few of his friends implore him to ask me to build sets for them. If I only had the time.