I got one of these used for $80 in 1975. I then got the Van Alstine hop-upinstructions and parts for $50 and did the hop-up, which consists of
1) replacing the tube half-wave rectifier power supply with a solid
state full-wave supply
2) replacing the tubes with new ones (Van Alstine said Sylvania)
3) replacing most of the other parts with better ones (metal-film resistors
and so on)
The hop-up, surprisingly to me, made quite an improvement in the sound. I
finally sold this amp about 15 years ago for $100. There is no question that
this amp was a lot of fun to fiddle with and listen to. It would play
amazingly loud for a 35-watt channel amp.

Performance? Well, IMHO, tubes amps are inherently inaccurate due to the fact
that their frequency response is affected by the electrical characteristics
of the speakers and speaker wire they are driving. So, any decent solid-state
amp is likely to be less-colored than any tube amp. Sound? That's in your
head!

Rock solid dependability.

So old I keep thinking about selling...

Model year 2000??? Ha!! I'm an original owner since 1959/60. The caps have been replaced with generic equivelants and tubes come and go. Otherwise, pretty much as I assembled the gear. Speakers are also from the same era...Electro-Voice 12" (re-coned) woofers and horn drivers in very large boxes.

I keep thinking about getting new gear. I'll spend a few days listening to equipment costing upwards to that of a loaded 4x4 SUV...and I keep walking away. I'd buy a used S-70 if my present amp ever suffers a "fatal error."

The reported "weaknesses" of the Stereo-70 seem to disappear with good ol' fashion drivers mounted in 7 cu ft boxes. CD's sound better with the Dynaco gear than when I plug in my backup "modern" (about 20 yrs old) Denon integrated amp. I have owned newer hi-end speakers that just didn't match well with the Dynaco gear. 105dB EV's are the way to blend with the characteristics of the S-70.

Smooth...glow-in-the-dark...lo-cost/hi-end sound. Trust your ears rather than the published specs.

Similar Products Used:

Dynakit PAS-2

I have had my Dynaco-70 for 3 years and am very happy with its overall response ranging from highs to lows in most music categories. When used with a decent CD player and using only a volume pot to control the volume it works quite nicely and complimented with a set of two way Dynaco speakers produces a rich and rather clean sound. The only thing that has been altered in the circuit of the chasis is the capacitors and some of the resistors and the speaker binding posts for ease of hook up. Tube layout is that of original equipment ,the volume pot I use is a Alps poentiometer short for Alpine and is a very good quality piece. I do not find it necessary to use a preamp or any type of controls to alter the treble and base as the reproduction of the natural sound is fine the way it is.

Sounds like music not HiFi

Not user friendly or convenient

If any of you guys want a real treat, just disconnect your 7199 heater filaments from the ST70 Power transformer and build an outboard power supply that provides the 7199s with regulated and filtered DC. All 7199s have heater to cathode leakage for some reason. Filtered DC gets rid of this problem and gives you a much more smooth, articulate amp with DYNAMIC BASS. The bass is not overdone but in character with the rest of the spectrum. The mod accomplishes this without destroying the musical quality the ST70 is famous for. It's easy to try this and back out if you don't like it, but you would have to be brain dead not to hear the improvement. You can get all the parts at Radio Shack for under $20. Enjoy, but don't do something stupid and fry yourself. This one simple mod is better than the 12 or so extensive mods I've listened to over the years. It puts the ST70 in the league of the real high end stuff without loosing any of the good character you love it for. Oh yes, never ever get rid of the rectifier tube for silicon diodes. The rectifier tubes is 75% what makes the amp sound so good and keeps the other tubes from wearing out with a soft power up.

Similar Products Used:

ARC D-40, D70, D115

Wow, I am impressed with the dynamics of this amp. For a 25-year old unit with old tubes to boot, this little (but heavy!) amp surprised me. Great dynamics and bass, obviously lacking a bit in clarity, and some mid-range "honk" on eg cellos. I got mine for $225 as a bit of a lark (ie OK for office listening and it looks cool :) and now I am seriously considering looking at more expensive tube amps for my main system. For the money and age, this amp is way better than you would think.

(The product year is not of course 2000, the web page made me do that...)

Similar Products Used:

None

simple design. great sound. well built.

Generally needs restoration work for top performance

This little power amp is probably the most popular vintage amp out there, possibly only second to Scott's venerable 299. The ST70 is an amazing performer that has many times suffered a bad rap which it has not deserved. It frustrates me to hear people put this fine amp down when in most cases the amp in question has never been properly restored, or was never assembled correctly in the first place. I own two ST70's and both sounded kind of drab when I got them. After I fully restored them, the sound was not only totally different, but very very good. Both of my ST70's now have perfect channel to channel balance with respect to both power output and frequency responce. Both are critical, and both are generally lacking in unrestored examples of this amp. Don't sell this one short. In correct operating condition, it is hard to beat, and a real bargain

Similar Products Used:

Scott 299C, Scott LK72B, H.K. A260,

My Dynaco is right now driving a pair of B+W speakers (don't know what model, small bookshelf things.) It's not a "perfect" system (find one that is,) but I don't listen to perfect records. It's an enjoyable, easy-to-fix, inexpensive amp; when it's re-tube time, you won't be in a bidding war with the entire audiophile world for a pair of NOS 300Bs. Tesla EL-34s sound pretty good ($20-$30/pair), and GT KT-66s ($150/quad) sound impressively muscular. Sound Valves, Angela, Triode and others offer some easy mods and improvements (Angela's website has a generous load of free info on all things Dynaco.)
Once again, it's not a perfect amp: It's weak in the bass, and the highs are pleasant but not breathtaking by any means. For the money, however, you could do way worse.

Stunning sound for the money, well built, and great conversation pieces.

Well, you wont find an original version of this amp that is newer than 20 years old. So some restoration is likely.

Thanks to Jack Mandall for a well written accurate depiction of what these amps are all about in an earlier review here. After reading his review I decided to give these amps a shot. I had just recently acquired an ADCOM GTP750 and needed some amps to go along with it in my main system. It took me over a month to find three amps worth owning, but I was able to do it for about $300 per amp. I immediately re-capped all of the amps, resoldered suspect joints, etc. etc. I also re-tubed all three amps with Svetlana EL34's, NOS 7199's, and a rectifier on one unit. I opted for a subwoofer, in this case a Velodyne that does a very credible job. Fronts are B&W604's with 603's in the rear and two shielded Paradigm Atoms at center. When I played the first song on this setup I realized immediately why so many people are buying these amps, and copying these amps. But there is something about these older Dynaco units that defies description or objective measurement. The only components that can't be copied as good or better than they made back then are the transformers and I suspect they play a significant part in the sound you get from these spectacular little amps. Someone earlier mentioned these amps being a new stereo merchant's worst nightmare. I think it goes way beyond that. With minimal effort and very little money these amps easily blow away 90 percent of the crap being sold out there. Be sure to choose efficient speakers, and keep these amps away from the kids because of the voltage potential if you run them cageless. Also, do not confuse these amps with the amps being sold by the "new" Dynaco, they are not the same.

Similar Products Used:

Sonic Frontiers, McIntosh, & Sound Valves.

Excellent sound quality, quite loud

Needed a tube preamp to go with it, which set me back $130; also needed work (but what vintage gear doesn't?)

I was tipped off to the availability of one of these by a friend who bought another ST-70 from the same store, and said he would've bought the ST-70 I wanted so he could run both of them bridged had I not bought it (see two reviews down). I replaced the molded-paper capacitors, the bias supply selenium rectifier and the bias supply filter capacitors before powering it up. When I turned it on, it worked but had flabby bass in the left channel. Temporarily replacing the EL34s in that channel with 6L6GC types solved the problem, but I decided to replace all the EL34s (three Japanese EL34s with one mismatched Mullard thrown in) with a matched quad of JJ/Tesla E34Ls. This made it sound much better, and increased the loudness dramatically. It soon replaced my Heathkit AA-151 as the centerpiece of my tube stereo system. The sound that this amplifier puts out is terrific. It may not have a whole lot of bass, but the tone controls on my preamplifier takes care of that. My stereo system is:
Amplifier: Dynaco Stereo 70
Preamplifier: Dynaco PAS-2
Tuner: Fisher FM-50-B
Turntable: Bang & Olufsen Beogram RX2
Cassette deck: Akai GX-F31
CD player: Sony D-EJ611
I highly recommend this amplifier, but ST-70s, like all vintage stereo hi-fi components, need restoration before they can be considered reliable. I recommend that all tube equipment novices take a look at my ST-70 troubleshooting page at http://www.angelfire.com/ma2/AdamVon/dynaresto.html .

Similar Products Used:

Heathkit AA-151, homebrew 60FX5 monoblock amplifier, lots of SS receivers

Sweet, transparent smoooooooooooooth sound.

Pricey tube complement.

I was tipped off to these gems by a friend (who's incidentally waiting to buy the other one available, but better hurry, I may have to run two of these bridged!)

I did some cursory research and found this is a respected, commonly available tube amp with an easily repaired/upgradeable design, with extensive documentation. Sounds like a no-brainer to me.

This particular unit had been gathering dust at a local shop for some time. I pulled the cover; Hm. Carefully noted the locations of the GE EL34's for correct reinstallation, and washed all the tubes carefully. Has GE 7199's and an unknown rectifier tube. Spent a couple hours vacuuming the chassis and cleaning with windex. Not too bad! Gotta love glowing bottles and nickle plate chassis.

Contact cleaned all the sockets and connecters. Cord looks okay, and nothing out of the ordinary under the chassis. The 4 way electrolytic has been replaced at one time, a rather odd looking gold cardboard can is there, along with mallory orange caps. One of the '34's is a 'fat boy' design, RCA I guess.

Well, what the hell. The fellow said it worked fine, and he's sold me good gear in the past, though I was skeptical. Triple checked all connections, and fired er up. All tubes lit up, and a very slight 'hum' could be heard from the (heavy) bank of xformers.

For test purposes I drove a pair of JBL Control 12SR reference monitors through a US made Carver C20 sonic holography preamplifier. The amplifier is dead quiet even at high volume levels, which I assume is a good sign. After three hours of a modern jazz 'test' tape, I'm impressed. The center xformer got noticeably warm to the touch after moderate listening levels, but not more.

Wow!! -- now I know why people go to such extremes for good sound-- silky smooth to the ears-- very listenable, this is the amplifier that will put you to sleep with a smile on your face. Who says it doesn't have any bass? I could swear I was running more than two speakers, the soundstage was that wide.

I'm sold on this excellent design.

Similar Products Used:

Nothing like this.