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In Reply to: RE: Has anyone built the new Dynaco ST-35 kit? posted by airtime on July 25, 2015 at 08:52:28
Why? The original was not a good amp.
Dynaco, in my opinion, built a few good monoblocks, and some very nice loudspeakers, but the rest of their stuff was mediocre at best and often crap.
Follow Ups:
In general all the Dynaco tube amps, including the Stereo 70 were considered very good amps in their day, just a smidgen behind the Marantz and McIntosh amps which were considered the super amps of the day. And, of course, the Dynacos were the winner of the performance per dollar events.
Just as I recall Gordon writing in the '60s -- O, Nostalgia!
Jeremy
The St-35 is a workhorse amp. Our local Mac repair center used one for decades as a bench amp. Not only that, but the EL-84 based amps boasted the sweetest sound from any Dyna product. Many, and not limited to myself, consider the small Dyna iron to be their best ever output transformer.
Of course, Dyna built their products to a price point and employed inexpensive parts. Still the basic platform was decent, if not first class. Perhaps the prevalence of the numbers they churned out makes many believe that they were not very good (ST-70's production numbers are close to half a million). The fact that the majority were sold as kits also makes their construction very dependent on the kit builder, too. That can make a noticeable difference in sound and performance.
Still I would not look down at Dyna gear especially after restoring and modifying many.
I won't get into the sweet sound debate, which is subjective, but the Heathkit UA2 monoblock was a very fine EL84 amp, more conservatively designed and operated, did not have the problems that the ST-35 had, and did not require extensive redesign/rebuild. I known that Dave O'Brien, who conducted the McIntosh clinics, had a high opinion of the UA1 and 2, and had a chart of it in his book as an example of an excellent competitor's amp.
I don't recall doing it back in the day -- probably because I wasn't much impressed with the ST-35 -- but I would be confident putting a pair of stock UA2s up against whatever has been done with the ST-35.
Yes ! UA-1 and UA-2 were fine performers...very favorable reports noted through the years. Original Quad ESL owners loved the UA amps.
I imagine a Dyna ST-35 built with twin power trannies, as in dual mono, with more conservative B+ HV operating points (i.e. choke input filters), independent bias for each channel, plus beefy power supply cap banks could be even more favorable...
nt
The Dyna SCA-35 had a lot of issues with heat. The ST-35 was a different animal. Same outputs but with a 7247 input, whereas the SCA 35 had a 7199.
The ST-35 ran hot, baked, cracked and warped circuit boards and burned up output tubes. There are several accounts to that effect right here.
The arguments seem to be that, if you do A, B, C and/or D, the ST-35 can be a good amp. My point is that Dynaco did not do that and the amp, as designed and built, had serious problems. If you were selling stereo equipment responsibly you would not have recommended it, and I didn't.
Worked on several St-35's. two were bench amps for a repair shop and on all day 6 days a week:
No burned boards.....
You're not differing. I said cracked and warped, not burned, circuit boards, and there is other testimony to that right here. I said burned with reference to the output tubes.
Our bench amp was an MC225. No problems there.
If you run tubes as hot as Dyna did with the ST-35, the circuit boards of that time were a poor choice, as experience with the SC-35 has shown. I think that was the main reason for my indifference to the Dyna at the time. However good it may have sounded, it was not going to be reliable. When you sell the things, that is important.
During my time in the business, when it came to kits, I spoke well of Heath basic amps, confidently sold EICO kit amps, integrated amps, tuners and preamps, and sold the occasional Dyna to those who insisted on it. My own gear was Mac.
Yes, the Z565 O/P transformer (OEM or "clone") is a price/performance champion. That "iron" also works very well in non-Dyna designs, including the "El Cheapo" I'm associated with.
The single RC bias network for all 4 O/P tubes is "Cheap Charlie", but is easily corrected. A pair of inexpensive, low noise, UF4007 diodes in the PSU is the another (IMO) obvious tweak.
The Dyna ST-35 is quite decent. Yes, there are better 6BQ5/EL84 amps available, for a price. TANSTAAFL!
Eli D.
Yes ! The original stereo amp ran hot and cracked the phenolic boards in time. Yet, nobody I know has ever heard of a blown PA-774 power tranny. Using a good Stereo 35 with vintage Euro or UK EL84s and 7247s will be a rewarding sonic experience.
Upgrading the boards to teflon, rebuilding the power supply sensibly, replacing the few caps sensibly, plus separating the cathode bias arrangement for each channel if quads of EL84s are unavailable could be what the doctor ordered...Stereo 35 is one fine stereo amp.
I have not seen a "new" version, but I can envision one with two power trannies, a la dual mono, plus a bit more conservative operating voltages for the outputs; but the Z565 output iron is hard to beat...
IT,
You don't have get conservative with the B+ rail voltage, if you use Russian 6Π14Π-EB (6p14p-ev), AKA EL84M, O/P tubes. The Russian bottle is a VERY tough 7189 equivalent whose sonics are good. "Monkey" with the small signal triodes to get the desired voicing, perhaps P2P wiring and a 12AX7 and a 6CG7 shared between the 2 channels.
You might want to contact "inmate" Jeff Yourison about the vacuum rectified (2X 6CA4/EZ81) "El Cheapo" he built around the ST-35 "iron" package. NICE!
Eli D.
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