Chicago_Pete Posted November 29, 2005 Share Posted November 29, 2005 Hi guys, I just picked up a pair of super nice looking ST 70s. Came my way of trade bait towards a pair of JBL 150As. Owner updated them with newer caps, tubes, whatever. I have to admit that I always considered these more of an entry level tube amp but I was set back by the quality of sound. They really sound good! Never too old to learn I guess. My rookie Dynakit question is, What's up with the stereo / mono switch? Both sides still stay active? On my Mac 225 the right channel becomes mono. Thanks, Pete Quote Link to comment Share on other sites More sharing options...
NOSValves Posted November 29, 2005 Share Posted November 29, 2005 The mono switch just simply connects the two inputs together. Those ST70's look to be in great condition! Craig Quote Link to comment Share on other sites More sharing options...
Chicago_Pete Posted November 29, 2005 Author Share Posted November 29, 2005 Hi Craig, If I wanted to run them as mono amps, what happens after I throw the switch? Does the left or right channel now become 70 watts output? Pete Quote Link to comment Share on other sites More sharing options...
sunnysal Posted November 29, 2005 Share Posted November 29, 2005 an ST-70 is NOT a starter amp! (as you discovered) when nicely freshened and used with the right ancillary components it can be someones last amp. if you decide to dump it I am sure you will find no shortage of people who are willing to take it off your hands! re: mono switch I thought that craig was right, that the switch did not affect the two ooutputs it simply combined the inputs...maybe I am wrong. I am sure someone else will ring in here, I avoided the stereo/mono issue by buying the MkIVs which are basically the st-70 rendered into monoblocks...sweet! enjoy! tony Quote Link to comment Share on other sites More sharing options...
sfogg Posted November 29, 2005 Share Posted November 29, 2005 " Does the left or right channel now become 70 watts output?" Neither, you have to strap them together then run the speaker from that. I use to run mono-blocked Stereo 70s but I prefered using a phase inverter to do it then strapping them for mono. Shawn Quote Link to comment Share on other sites More sharing options...
NOSValves Posted November 29, 2005 Share Posted November 29, 2005 Shawn would be correct there would be a advantage to doing a perminent wire job with a single phase inverter but not everyone is going to easily accomplish such a thing. To bridge your ST-70 throw the switch to mono and hook up one input from your preamp to one of its RCA inputs. Then run 2 small pieces of wire from the left 0 ohm tap to the right 0 ohm tap. Repeat this on the two16 ohm taps then attach your speaker wires to either left channel or right channel 0 ohm and 16 ohm and your done. This is if you want a 8 ohm impedence. You can strap the two 8 ohms together for a 4 ohm impedence and the two 4 ohms for a 2 ohm impedence. Craig Quote Link to comment Share on other sites More sharing options...
Chicago_Pete Posted November 29, 2005 Author Share Posted November 29, 2005 Hi Craig, This seems like a solution in line to my ability. A couple of jumpers and IM in. Thanks much, Pete Quote Link to comment Share on other sites More sharing options...
NOSValves Posted November 29, 2005 Share Posted November 29, 2005 Yup give it a whirl! Quote Link to comment Share on other sites More sharing options...
dlb945 Posted November 29, 2005 Share Posted November 29, 2005 I rebuilt a pair of ST-70's for a friend using 100% original design but with closely matched capacitors/resistors for left/right channels as well as a beefed up power section. As a test, I strapped the outputs as described above and wired to my K-Horn's with ALK crossovers. The preamp was my favorite Marantz 7T (solid-state) with updated and matched capacitors/resistors and upgraded power section as well.The 3-D image was to "die for" and was a total surprise. The extra wattage provided by strapping gave a range of dynamics close to a 250 watt/channel solid-state amplifier (my Hafler DH-500) but with that slightly warmer sound that a tube amplifier can give.I was reluctant to return the ST-70's to my friend and kept them for about 3 months. As a point of interest, I am now rebuilding the first of two ST-70's for me so that I can duplicate the first experience.I'm sure that the ST-70 is not a world class amplifier by today's standards but ... I'll bet it will get you close and for 2% of the price, you can get to 95% of the sound. A bargain by any measure. <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /> http://home.bellsouth.net/p/PWP-dlblabs Quote Link to comment Share on other sites More sharing options...
Chicago_Pete Posted November 29, 2005 Author Share Posted November 29, 2005 Finally someone who also respects the lowly Marantz 7T. Too funny. I used to have one of them until enough people (who never heard it) told me it was junk and I sold it. I thought it was a great unit for the money. I plan on giving these amps a whirl as monos. I was initially impressed with the condition of these 70s and the fact that someone had already completed the rebuild. The great sound is icing on the cake. Pete Quote Link to comment Share on other sites More sharing options...
dlb945 Posted November 30, 2005 Share Posted November 30, 2005 I love my Marantz 7T but, it took a while to love. I won the unit on an eBay bid and the seller said "It runs well." It did run well but it had a hard edge to the highs and after about an hour of listening, I found myself shutting the system down and switching to the television. Hmmmm! I joined a Yahoo Marantz forum and asked what folks thought about the 7T. Most responses were negative except for one from Sweden. This person was once part of a team doing repairs for early Marantz units in Europe and he was quite high on the Marantz 7T Preamplifier and Model 15 Amplifier. He had several suggestions for updates on both units and I started with the 7T replacing 5 each 15 ufd electrolytic capacitors in the signal path on two of the "air boards" in the system. I used very good film/foil replacements. The project took about two evenings. What a difference the changes made!!! The preamp was not only listenable but became my favorite. In side-by-side comparistons with the tube based Marantz 7C, I like the 7T more and although the sound stage is slightly less deep, the detail around singers and instruments are far superior. I have tried a few other updates including the power supply, some selected resistors in the signal path, and some low-noise transistors but these changes made little improvement to the sound. I own and cycle a few other preamps into the system but always go back to the 7T. My next best Marantz surprise was a beat up Model 15 amplifier also won on an eBay. With a few minor updates, it is making great music and the best amplifier for rock. I still prefer tube amplifiers for classical/opera at this time. >>>Dan Quote Link to comment Share on other sites More sharing options...
Chicago_Pete Posted November 30, 2005 Author Share Posted November 30, 2005 Hi Dan, Very interesting story. I dont have your expertise to experiment with swapping caps and resistors, wish I did. I kind of like using a solid state pre with tube amplifiers. Although IM not running that now, I feel a SS pre seems to put some snap back if that makes any sense? Perhaps IM mistaking brightness for pace? My Marantz 7T ended up going to Japan. New owner was very happy with it. I just picked up a Marantz 3300. Things I don't want or need have a way of finding me:) Pete Quote Link to comment Share on other sites More sharing options...
sunnysal Posted November 30, 2005 Share Posted November 30, 2005 I STILL love my 7T and use it in my main system. I upgraded the caps in the signal path and loved the results. Tony Quote Link to comment Share on other sites More sharing options...
Chicago_Pete Posted November 30, 2005 Author Share Posted November 30, 2005 Hi Tony, Just read your post. I also use the Audioquest Diamondbacks. These interconnects are great! Once in a while Audio Advisor has a sale. Pete Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.