Wardsweb Posted February 15, 2016 Share Posted February 15, 2016 Some of you may remember my build of a re-envisioned amplifier based on the Dynaco ST70. I basically took an original ST70 as my source of inspiration, used only the output transformers from it and built an updated version from scratch. 5 Quote Link to comment Share on other sites More sharing options...
Wardsweb Posted February 15, 2016 Author Share Posted February 15, 2016 (edited) Well, I sent the amp off to Craig at NOSValves for him to do his magic. Some tweaking and fine tuning some parts and it is better than I ever imagined. This thing is dead quiet. Here are some screen shots: 20 Hz 200 Hz 5 KHz 10 KHz and last at 20 KHz Edited February 15, 2016 by Wardsweb 1 Quote Link to comment Share on other sites More sharing options...
Wardsweb Posted February 15, 2016 Author Share Posted February 15, 2016 If you would like to know more, here is a web page I put up on the entire build. http://wardsweb.org/audio/ST70/ 2 Quote Link to comment Share on other sites More sharing options...
Jim Naseum Posted February 15, 2016 Share Posted February 15, 2016 Is this using the ultralinear taps? A concertina splitter? What's the circuit like? Quote Link to comment Share on other sites More sharing options...
Wardsweb Posted February 15, 2016 Author Share Posted February 15, 2016 Is this using the ultralinear taps? A concertina splitter? What's the circuit like? You can see the schematics on my website http://wardsweb.org/audio/ST70/ Craig suggested I add a switch to be able to switch in or out ultra linear mode. Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted February 15, 2016 Share Posted February 15, 2016 Stunning Luther! 2 Quote Link to comment Share on other sites More sharing options...
mustang guy Posted February 16, 2016 Share Posted February 16, 2016 That is one beautiful design. I love it.... 1 Quote Link to comment Share on other sites More sharing options...
Wardsweb Posted February 16, 2016 Author Share Posted February 16, 2016 (edited) If you have the building bug, it's easy to catch, try Maynard's "Little Sweetie" build. Very easy circuit as most SET's are and you will be rewarded with another great sounding easy to build amplifier. I saw the thread and will keep it in mind. For now, I'm taking a break from building things and actually listening to music. So many amps and so little time. Edited February 16, 2016 by Wardsweb 3 Quote Link to comment Share on other sites More sharing options...
oldred Posted February 16, 2016 Share Posted February 16, 2016 That is Fricken Nice..... So you used that old brown thing for inspiration to build that beautiful amp..... Damn nice. And....... How does it sound? And why does it look like your system is outside...... Near the Lawn? G.E.M Quote Link to comment Share on other sites More sharing options...
Wardsweb Posted February 16, 2016 Author Share Posted February 16, 2016 That is Fricken Nice..... So you used that old brown thing for inspiration to build that beautiful amp..... Damn nice. And....... How does it sound? And why does it look like your system is outside...... Near the Lawn? G.E.M This system is in the sun room. It has glass walls, so it looks like it is outside in the that picture. The curtains block sunlight and act as diffusers so I don't get all the reflections off the glass. Here is an old picture to give you a better idea of the layout. The speakers are 1968 JBL C50 Olympus with some custom JBL 2397 "Smith horns" JBL 2405 tweeters. 1 Quote Link to comment Share on other sites More sharing options...
NOSValves Posted February 16, 2016 Share Posted February 16, 2016 (edited) The circuit in this reworked ST70 utilizes Shannon Parks ST70 front end which is 1/2 12AX7 in each channel for input driver into a constant current source longtail pair 12AU7 phase inverter. I would have rather had Luther point to point wire with my own circuit it but at the time we put this package into the planning stages I was really buried in work and personal life so I pointed him to Shannon board since IMHO it is the best ST70 circuit board based front in on the planet. Shannon parks circuit is not that awful far removed from my own. Mine is just a bit more transparent since it is directly coupled so one less cap in the signal path. The best coupling cap on earth is no coupling cap at all! I tweaked many of the cap value and tuned the feedback for really nice square waves across the 20 hz to 20khz audio ban This amplifier sounds and performed absolutely great for what it is! Luther left out the 10 hz screen shot which shows the ST70 output iron is really good for the small size... All the square waves were performed at 5 volts RMS AC volts on the 8 ohm taps with a 8 ohm non-inductive load. Imagine what they would look like at 500 mV. The amps also makes 41 watts before clipping with both channel driven well above what an ST70 would ever think of doing (about 30 at most). This is mostly because Luther used an upgraded power transformer along with a much larger filter bank especially at the center tap of the output transformers that does not run out of steam like the original Dynaco did in a painful manor. Edited February 16, 2016 by NOSValves Quote Link to comment Share on other sites More sharing options...
Wardsweb Posted February 16, 2016 Author Share Posted February 16, 2016 Craig I can't thank you enough for your help with this. You have forgotten more about tubes and design than I will ever know. I do appreciate your patience and understanding that while I can execute a design in a meticulous manner, I actually know little about circuit design. Quote Link to comment Share on other sites More sharing options...
Wardsweb Posted February 16, 2016 Author Share Posted February 16, 2016 Here is a picture from the working side. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted February 16, 2016 Share Posted February 16, 2016 (edited) Luther,You have this down pat! You only made one ground connection mistake and it was good that it ended up here for testing and minor tweaking.You absolutely do not need to thank me you have saved my butt with my website countless times over the last dozen years, always a joy to deal with..so in the end I will owe you forever..Next up you should build your visual rendition of what will be known upon release as the NOS Valves Signature series VRD powered by Magnequest. I'll give you the entire design and you go wild with the aesthetics...I already upgraded one pair of VRD's with a cost no object transformer from Mike Laferve from Magnequest then tuned the circuit to the new awesome iron. I have to give Paul Hovenga www.manymoonsaudio.com thanks for the trust and cash to allow this to happen. Talk about paying to be a guinea pig!IMHO this takes the already awesome VRD performance to absolute high dollar giant killer level. Edited February 16, 2016 by NOSValves Quote Link to comment Share on other sites More sharing options...
CindyJarvis Posted February 16, 2016 Share Posted February 16, 2016 Very nice looking amp!!! I am a bit perplexed to why one would test an amp capable of 35-40watts at only 3 watts. I would think a high power amp should perform well up to it's rated limit. -Cindy Quote Link to comment Share on other sites More sharing options...
paul79 Posted February 16, 2016 Share Posted February 16, 2016 Cindy the Sloth? xxxJPMxxx is BACK!!! Quote Link to comment Share on other sites More sharing options...
NOSValves Posted February 16, 2016 Share Posted February 16, 2016 Very nice looking amp!!! I am a bit perplexed to why one would test an amp capable of 35-40watts at only 3 watts. I would think a high power amp should perform well up to it's rated limit. -Cindy Hmmm showing your absolute lack of reasonable knowledge garnished from experience....fine by me. Quote Link to comment Share on other sites More sharing options...
CindyJarvis Posted February 16, 2016 Share Posted February 16, 2016 (edited) Yes I am new to tube ampliers. This is why I ask you gurus questions I think the higher frequencies need not not be tested at full output, its not needed. Maybe 50% full output. Since there is no RMS with square waves I would like to see 20v peak to peak. -Cindy Edited February 16, 2016 by CindyJarvis Quote Link to comment Share on other sites More sharing options...
NOSValves Posted February 16, 2016 Share Posted February 16, 2016 Yea I'm going to bother wasting my limited time with something that useless for The Sloth aka xxxjpmxxx go try it with your own amplifiers then show us your results..... 10 Hz to 20khz please....you do it and I will.... Quote Link to comment Share on other sites More sharing options...
NOSValves Posted February 16, 2016 Share Posted February 16, 2016 Yes I am new to tube ampliers. This is why I ask you gurus questions I think the higher frequencies need not not be tested at full output, its not needed. Maybe 50% full output. Since there is no RMS with square waves I would like to see 20v peak to peak. -Cindy Um I was using a RMS volt meter and that is all that was meant by that smartass....keep baiting and you will be under a new name yet again. Other wise get lost... Quote Link to comment Share on other sites More sharing options...
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