Dynaco ST-70 totally restored vs Dynaco ST-70 Kit

Hi Everyone, I'm planning of buying a Dynaco ST-70 but I don't know which one sound better, the Dynaco ST-70 totally restored vs Dynaco ST-70 Kit(both are on sale here in Audiogon right now). I'm also thinking of Primaluna Prologue amp. How does this sound compared to the Dynaco?
IMO: Some of the ST70's I have seen here are beautiful. But... They still have the same circuit as the original amp. I would prefer a new input board with all new tubes that are different from the vintage 7199. The 7199 was a good tube 40 years ago but beter circuits are available out there that simply sound better. The 6G8H add a whole new world of resolution as well as 12AX7's, EL86?, 6SN7's and more. Making the B+ stiffer, and improving the power supply and tube bias removing the old power transformers and putting in a new one that can handle the extra voltage, removing the quad capacitors and strengthening
My ST70 has been with me for over 10 years and I have had it tweaked many times to get it where it is today. I have a $2500 amp here also (VTL ST85) that is still not superior to the ST 70 in my system on my Spica TC60's. I bought the VTL amp to drive a larger pair of fullrange speakers. But I have not found a pair yet so the VTL may find itself on the market soon. I don't think the ST70 mods go far enough with the improvements that warranty spending $700 plus. Trust me the circuits have not changed in the past 50 years so don't believe the hoopla!

I would have to go with the Primaluna Prologue amp because it has built in all the improvements like adaptive bias, a very good circuit for the input and of course your choice of output tubeslike EL34's or 6550's, and more. You will have more versatility and you will be able to hear the different flavors of each tube it can work with. You can't do that with the ST 70. And trust me I love mine and I haven't heard many amps up even up to that $5000 mark that blows it away. But if I were to look for a new amp today I would be looking at the Primaluna for sure.
Second Ponnie's take on things.Good luck,Bob
A dissenting opinion. I would go with Bob Latino's kit. The power transformer is beefed up over the original Dyna transformer, being a 5 amp job, the input board is the all triode Tube4Less board with individual bias for each tube (I prefer fixed bias to cathode bias). All the parts are new, many being American made. Basically, this addresses the weaknesses in the best selling amp of all time and makes this classic great for everyday use. I would also point out that all of the parts are available, most from multiple suppliers, so that should your Dyna break, now or in 20 years, there will be constant support for the amp.
i am considering a stereo 70 myself. i will only buy an original, stock stereo 70. if i want more "resolution", i'll buy another amp.

why take an orange and turn it into an apple, when you can buy an apple ?
Does Primaluna uses cheap parts compared to the Dynaco ST-70 Kit?
The Primaluna is made in china(cap omitted intentionally). That should answer your question.
am considering a stereo 70 myself. i will only buy an original, stock stereo 70. if i want more "resolution", i'll buy another amp.

why take an orange and turn it into an apple, when you can buy an apple ?

Me too! The power tranny in the original model is fine, no need to step up to a larger rating. if not, why do they last more than 20+ years and counting?

For me, I am bias to the true original output transformers the ST-70 uses. I agree, that the input board needs to be replaced (I use one with 6922 drivers) as well as the power supply main caps (if not replaced already!) and the selenium rectifier. I heard and compared other ST-70 wannabees (not the original power and output transformers) and to me, there is no substitute for the original.

My opinion only.
I would agree and disagree with Amadarae. The original Stereo 70 power transformer, runs very hot and this bothers some people. On the other hand, as he points out, many of these are fourty years old and functioning perfectly.

What the original design does not take into account is that the aftermarket driver boards that are so popular, add the filament current draw of from one to five extra small signal tubes. This additional current draw can certainly put stress on the transformer beyond the design envelope. Some of these boards use octal drivers like 6SL7 and 6SN7 that are particular current hogs. And yes some original transformers can last another fourty years with even the added current draw of additional tubes. And, of course, if you have converted B+ rectification from the 5AR4 tube to solid state rectification than you have decreased the current draw on the transfomer.

i am considering a stereo 70 myself. i will only buy an original, stock stereo 70. if i want more "resolution", i'll buy another amp.

why take an orange and turn it into an apple, when you can buy an apple ?

Agree 100%. I have a completely UNRESTORED ST70 in pristine condition. It makes my (restored!) Quad ESL 57s sound incredible.

If you don't like the original, get a different amp.
hi jeff:

i too have restored quads,namely, quads unlimited esls.

i am looking forward to auditioning the stereo 70.
so you use mullard el34s, some other nos tubes, or some current production tubes ??
yes. mullard el34s -- from the blackburn factory.
I too use Mullard El-34's/6CA7's. I have accumulated 3 pairs all NOS and should be enough. Took me a while to shop, test, and burn in to see if it holds bias current to arrived at my "set". I never had any luck with the metal base ones though (Noisy and un-stable). Oh, btw, I highly recommend to have a reliable tester when buying NOS EL-34's.

FWIW, I never considered my power tranny as "very hot" when operating. I just got lucky perhaps because my unit is pristine (you can tell signs of burning looking at the original enamel paint of the power transformer and also how the original paper base input board looks like inside). I bought mine for $295 way back with original cage, Mullard 5AR4 rectifier, RCA 7199 drivers and Mullard El-34's and all test great.

You can see my unit on my system page here (Winged-C Output tubes) with the Curcio input board with Yageo metal film resistors, Orange Drop caps, and 6922 driver/splitter tubes. I was thinking of replacing the input board caps (from Orange drops to PIO's) but really like what I am hearing so I kept it as it is.

I tried my amp on Magnepan(1.6), Bozaks, Fostex base MLTL, and now my Altec 604's in OB and sounds really nice (except on MG 1.6 where I can only listen at low levels).
I have a friend who has a Polk Audio Vintage speaker (big ones with 4 woofers and 4 HF drivers) and so happened to try the ST-70 there, it sounds pretty nice. My friend wants to buy my amp on the spot. I replied by saying to give me a couple of weeks (I want to shop for a comparable unit to replace the one I have but all I saw during that time are not as mint). That was almost three years ago. I still have my amp.

One other thing, in mono mode (using mono cartridge, and phono preamp), the ST-70 will surprised you thinking that you bought a mega-dollar amp even if you use Winged-C (highly recommended provided that you burn it in for about 12 hours before critical listening)instead of the Mullard 6CA7's.

So in retrospect, give me an Original ST-70 or give me a different amp. Life is too short to waste time on copycat's.

Oh, with regards to "whatever his name" selling kits for the ST-70, follow the link below. If this is not "self promoting" post, I do not know what it is.


In a public forum, is it wrong to post something good about what you are currently selling? I do not know.
I have to disagree with Rodman on the Prima Luna. here is a write up of the components that are used with the Dialogue integrated,which is the same throughout their line.

"ALPS volume control. Nichicon and Realcap capacitors. Gold plated heavy duty speaker terminals and gold plated input jacks."

These are not cheap Chinese components.Yes it is assembled in China, but if you look at the point to point wiring you will see that it is very well done indeed.
Also the entire design is done in the Netherlands,and these components are all european.So what you are getting is a Euro design,assembled in China to keep costs down(and margins up).

It does however come with Chinese tubes,but tube rolling is what this thing does best,since it can use EL34,KT88,and 6550s with auto biasing taking care of itself.

I am also curious about the auto biasing in respect of tube life. If the cirucits are always in perfect bias does this help keep the tubes in better shape longer? Also does this mean they sound better longer?

That said, I am very interested in a Dynaco St70.Since these beautys are quite "vintage",doesn't it stand to reason that the caps MUST be replaced? Also I understand that the original rectifier is downright dangerous and also must be replaced with a diode/solid state version?

I have also seen full Triode versions of the Dynaco,how does it sound and what are the specs?

What I am very curious about is the cloth lead transformers sounding better than the new and sometimes more powerful replacements. When looking at ads on Agon and Ebay, the cloth lead originals are always stated as desirable.Is this true? Also,are the new boards available the same circuit,recreated or are they tweeking the sound? Which one sounds better, and why?

curious mind needs to know

Out of curiousity -- Has anyone out there built a Triode Electronics or Bob Latino kit , listend to it long enough to a "fix" on the sonics and replaced the output transformers with oridinal Dynaco's ?