[roymail]

I've never owned a tube amp, but have been a music lover for many years.  I continue reading about them and lately have been eyeing some fully rebuilt Dynaco St-70's on Audiogon for what appear to be reasonable prices.

I have a Luxman active preamp, but I prefer using a diy Goldpoint passive in my single source system.

Anyone think this would be a good place to get a taste of tube amp sound?  Thanks.

[mark funk]

A stock rebuilt ST-70 well sure sound like a tube amp. I guess if you can get a clean one for not a lot of bucks that would be a good place to start and there are many upgrades for the ST-70. I heard one upgrade for the ST-70 by Frank Van Alstine and it sure sounded good and there are many others. The ST-70 is a good DIY amp to play with.

                                                                                 

[oneinthepipe]

I am not very knowledgeable, and I only own one tube amp, an AVA Ultimate 70, but I used to own a pair of ST-70s, many years ago, and I think that the stock ST-70 sounds tubby (not just tube-y, but tubby).  The ST-70 has "paper bag bass", and the bass lacks the definition and extension that are exhibited by better tube amps.

The AVA Ultimate 70 uses ST-70's chassis and power transformers but is otherwise a different amp.  You can take an old ST-70 and modify the amp into a U70, but unless the donor amp is very inexpensive, the cost will exceed buying a used U70 or another amp. 

In the stock form, I think that there are many better choices than an ST-70.

[Niteshade]

I think the ST-70 is a great starter amp and possibly a great amp to think about beyond a starter system. The iron is good and the circuit isn't bad! Best of all, their cheap!

[roymail]

Hi, Blair... glad you jumped in.  Thanks for the shout out.

[Niteshade]

A used ST-70 is around $360.00 on average. You can't go wrong with that. You can get rebuilt ones for that much and up to around $500.00. Ebay is the best place to look.

[JohnR]

Like many others here I suspect, I have a soft spot for the ST-70, as it was my first tube amp and at one point I owned several of them.

Personally, I would say if you would like a taste of classic vintage tube-o-philia, get one that is basically stock but operational, and enjoy it for what it is. Then you can tweak and/or upgrade as you wish. If however you are looking for modern hifi, then start looking again with that in mind.

[roymail]

Can someone describe how the sound will differ from SS in the mids and upper end (subjective but go ahead and opine).

The main thing I dislike about my SS is that it can get rough on the upper end instead of remaining smooth all the way up.  I know, crap in and crap out, and I have some music that is gorgeous regardless of volume or hz.  I wonder if a ST-70 will change some of that.

Don't be shy. 

[Niteshade]

The ST-70 I owned had a smooth upper end and somewhat warm mids, but not too warm. It was easy to listen to. I wouldn't call it clinical, but it is a little on the bland side, at least in stock form. I prefer a more aggressive stance. It's a very easy to listen to amp.

[wilsynet]

I have limited experience of course, but the only very good SS amplifier I've heard that doesn't get rough at the high end is the Red Wine Audio.

I would not encourage you to find a ST-70.  Lots of people have soft spots for some of the older gear, and certainly there are bargains to be had.  But the high end has moved on and I think you are likely to be dissapointed.  Get something newer from one of our manufacturers here like Blair or AVA or RWA.  I know they all have home audition programs, so I would certainly take advantage of that.

[bregez]

The ST-70 is a great amp.  I would however get rid of the 7199 driver board and replace it.  The new production 7199’s are terrible and the NOS ones are pricey.  There are lots of options for driver boards on the market.  Once the driver board is replaced the amp is no longer a Dynaco and will sound different from the stock ST-70. 
http://www.tubes4hifi.com/ST70.htm
http://www.diytube.com/phpBB2/viewtopic.php?t=773
http://triodeelectronics.com/st70boards.html
I would also upgrade to 30/20/20/20 can capacitor with a new 80/40/30/20. 

[oneinthepipe]

The ST-70s that I owned lack the clarity, low end extension and definition, and the mid-range and high end presence that the AVA Ultimate 70 exhibits.  Prior to owning the U70, I owned an AVA Super 70i, a very well-regarded amp that was built with Dyanco transformers on an ST-70 chassis.  The Super 70i enjoyed two decades of positive reviews and was a tremendous step-up from the stock ST-70, IMO.  Then, last year, I had my trustworthy Super 70i upgraded to a U70 because the Super 70i was noticeably inferior to AVA's Insight-series solid state amps, as I had recently acquired an Insight 440.

The U70 is on a completely different level compared to the Super 70i, which was vastly superior to the ST-70, I thought.  The U70 is my preferred amp, and although the amp is only 30 watts per channel, the amp easily drives my full-range Salk HT2-TL speakers (86 db, I believe).  The U70 has deep, tight bass that rivals the Insight 440, and the U70's midrange and high end is glorious.  Both amps have excellent imaging.  The Insight 440, at 220 watts per channel, handles complex music with rapid, deep bass better than the U70, however.

The AVA Ultimate 70, either in kit-form or as a factory-installed upgrade, is a bargain.  I think that anyone considering an ST-70 or modification would eventually regret not inquiring about the AVA Ultimate 70 upgrade.

http://www.avahifi.com/root/equipment/amplifier/ultimate70.htm

The U70 is very similar in sound to the new UltraValve, which Robert Harley of TAS described as The Greatest Bargain at RMAF.

http://www.avguide.com/blog/the-greatest-bargain-the-rocky-mountain-audio-fest

[baldrick]

For what it's worth I did a restoration on an ST70 a few years ago.
I changed the driver circuit to use an EF86 pentode per side and a 12AU7 phase splitter.  The result was quite similar to the original 7199 pentode/triode configuration.  The EF86 is one of the nicest sounding input tubes available in my opinion.
I also replaced the quad can capacitor with discrete parts.
The rest was the usual - new tube sockets, new point to point wiring etc.
I used the original Mullard EL84s and Mullard 5AR4 rectifier.  The sound was much nicer than stock. Then I replaced the EL84s with new production Electro-Harmonix.  The amp became much tighter in the bass but maybe not so liquid in the midrange, and certainly cleaner in the highs. Then I tried a matched set of Sovtek KT66 tubes, rebiased it and listened.  I got the midrange liquidity back and kept the bass!
I think with the new input circuit and the KT66 tubes gave the revamped '70 quite an interesting sound....seductive is the word I'd use.
So to answer your question a restored ST70 is a perfect starter amp.  It's nearly impossible to screw up if you're careful and can handle a soldering iron.  There are a hundred different flavours of restoration and modifications out there and each has its merits and detriments.  What matters is that you enjoy the end result.

[Tyson]

I have a pair of ST70's, using the VTA boards, which are basically a copy of the circuit used by VTL for their ST85 amps.  They sound more modern than the original board, which means more linear, clearer, and more punchy.  I owned the VTL amps for a while before the VTA ST70's and I like the ST70's better, for a couple of reasons - 1, the use of the tube rectifier makes a big difference in sound, for the better.  More natural and tube-like.  2, the use of Paper in Oil output capacitors, which really have an organic sound in this amp.  Finally, I'd say that the 12au7 lower gain board sounds better than the 12at7 high gain board, at least in my system.  I have one of each, and they are close, but I think the 12au7 nudges ahead.