David_NC
Super Member
Last week, I finally got to test out my Dynaco ST-70. I 'refurbed' it a couple months ago but never got a round to finishing a few things and getting some somewhat disposable tubes to test it with. Last week, the tubes arrived, so I finally got to hook it up. The left channel sounded OK, not great, but OK. The right channel sounded like nothing; there was no output. I accidentally powered on the amp too soon after turning it off and promptly caused arcing in the 5AR4 rectifier tube. This time, I ordered two just in case. While waiting for the tubes to arrive, I spend a bit of time going over the schematic, checking the work I'd done, etc. I tested various points on the good left channel and compared values to the right channel. Everything looked good; a few values were different between the channels but not by a lot. At a loss for what could be causing the issue, I touched up every solder connection I'd made when replacing parts. The amp worked when I got it, so there really shouldn't be any reason, other than a possible bad solder joint, to cause the dead channel.
Yesterday, it was time to fire it up again. I plugged my iPhone into the inputs and connected a pair of ADS L520's to the 4 ohm terminals. I checked and made a few adjustments to the bias, after it warmed up. Now for the test - I got sound from both channels... not just sound, as in pops or other noises, but music. A friend, who had never seen a tube anything in person, was there see what it was all about, and I let him choose some tracks to play. Whatever we selected sounded really, really good. That's pretty much what I'd expect from these speakers; big ADS 2-ways just do a lot right, at low to medium loud levels.
After a couple hours of listening, I connected the amp to the pair of Dahlquist DQM-9's that I've been using lately in the garage. It took me more than a few hours to really warm up to these connected to an old 80 WPC Denon DRA-635R. They sounded a bit harsh at times, but they were also very revealing. Over time, I've really started to like them and appreciate them. They are efficient speakers (a bit more so than the L520's) and should do well with lower power. Well, suffice it to say that I'll have to spend more time with them on tube power. There was something lacking that was present on the Denon SS amp. On certain tracks, however, they are outstanding. I randomly chose different material to get a feel for how they sound - 60's-70's vocals and folk, a bit of jazz, Motown, 70's classic rock, house, EDM, and modern alternative. The Dahlquist were pretty hit or miss on many of those, but some were really good, as I mentioned. Oddly enough, a random Roberta Flack song was the best. It was way better on these than on the ADS L520's.
It'll be fun to spend some time with various speaker - source material combinations. I'll swap back in the original tubes that came with the amp soon and give them a listen. So far, I'm quite impressed with this little Dynaco ST-70 that followed me home from Goodwill. Even on 95dB efficient speakers, I notice no hiss from the tweeters, and there's no hum from the speakers whatsoever; this amp appears to be functioning as designed, at this point. Fun times indeed!
Yesterday, it was time to fire it up again. I plugged my iPhone into the inputs and connected a pair of ADS L520's to the 4 ohm terminals. I checked and made a few adjustments to the bias, after it warmed up. Now for the test - I got sound from both channels... not just sound, as in pops or other noises, but music. A friend, who had never seen a tube anything in person, was there see what it was all about, and I let him choose some tracks to play. Whatever we selected sounded really, really good. That's pretty much what I'd expect from these speakers; big ADS 2-ways just do a lot right, at low to medium loud levels.
After a couple hours of listening, I connected the amp to the pair of Dahlquist DQM-9's that I've been using lately in the garage. It took me more than a few hours to really warm up to these connected to an old 80 WPC Denon DRA-635R. They sounded a bit harsh at times, but they were also very revealing. Over time, I've really started to like them and appreciate them. They are efficient speakers (a bit more so than the L520's) and should do well with lower power. Well, suffice it to say that I'll have to spend more time with them on tube power. There was something lacking that was present on the Denon SS amp. On certain tracks, however, they are outstanding. I randomly chose different material to get a feel for how they sound - 60's-70's vocals and folk, a bit of jazz, Motown, 70's classic rock, house, EDM, and modern alternative. The Dahlquist were pretty hit or miss on many of those, but some were really good, as I mentioned. Oddly enough, a random Roberta Flack song was the best. It was way better on these than on the ADS L520's.
It'll be fun to spend some time with various speaker - source material combinations. I'll swap back in the original tubes that came with the amp soon and give them a listen. So far, I'm quite impressed with this little Dynaco ST-70 that followed me home from Goodwill. Even on 95dB efficient speakers, I notice no hiss from the tweeters, and there's no hum from the speakers whatsoever; this amp appears to be functioning as designed, at this point. Fun times indeed!