Restoration tips for Dynaco ST70 & PAS

[kjohnsonhp]

I am interested in suggestions on what to do with the Dynaco ST70 tube amp and PAS pre-amp found on ebay at

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=1381563623&rd=1

I've been cruising ebay because the recommendation on this board was to try tube amplification with my 1976 Cornwalls to improve the 2-channel sound over my SS receiver. My current reference point is based on lower quality electronics compared to my speakrs (80's Hitach 60w 2-channel receiver and Denon AVR-2000 DPL receiver). I've used both with my Cornwalls. My sources are a Beogram 3000 TT & Sony 207esD CD player.

I bid on the Dynaco because my friend recommended the brand and has restored three. He said he would do the work for the cost of the parts (and he has thousands of tubes being an antique radio restoration hobbiest). This auction had both an AMP and preAMP so once repaired I simply add my TT and Corns and start the testing.

This was an impulse bid so I must first ask:

1. Are either of these items worth keeping and using for 2-channel with my Cornwalls to determine if I prefer tubes over <$1,000 SS HT electronics? If this wasn't a great buy I could do minimum repairs and resell it. I'm also wanting to watch movies so I was thinking of a <$1k receiver for that purpose. If the Dynaco isn't a big sound improvement over say an Outlaw 1050 or Denon 3802 then it's not worth the hassle.

2. If it is a good starting point for trying tube electronics then should I simply clean and repair them or do you recommend certain modifications? This is probably the key question for this board.

3. Is the pre-amp a good match or do you recommend something else?

4. Should I buy a surround processor for HT and add more tube amps or use SS receiver for HT and the tube amp for 2-channel (or combine the SS receiver and tube amp.

5. This is equal or more money than the famous EICO HF-81 so if that's a better solution then I can resell the Dynaco and keep shopping.

I'd like to explore the tube sound based on all the rave comments on this board so I don't want to test a poor example. I have close to 3,000 lps so between my vinyl and my Cornwalls I probably a good canditate for tubes...(not the kind that go in babies ears or the kind that get tied).

KJ

"Persistent Memories"

-November Group

[kjohnsonhp]

I've got the following perceptions:

1. Dynaco ST70 is a great beginner tube amp because they are plentiful, relative simple to repair, and have lot's of parts and upgrade options.

2. However, they seem to need the upgrades for quality sound as mentioned on this board.

3. There are several sites for drop-in replacement boards, parts, manuals and upgrade suggestions including the Van Alstine kit or refurb.

[Mallette]

You will get LOTS of varying opinions on the board. However, I believe the ST70 is generally considered perhaps the single most effective VT amp ever designed. Only you can decide for yourself. I've a Van Alstine refurb that I am totally happy with. It drives two K'horns, a Cornwall, and two Heresies (DynaQuad w/center tap) all the levels I could wish and I can hear absolutely nothing wrong with my system atributable to it.

The only thing that tempted me in the price range was a 3 watt SET monoblock pair that was a just a bit more. However, until I can test someone elses I remain unconvinced of the ability of a 3 watt amp to provide the levels I need with pipe organ, big band, or hard rock.

If you're handy with an iron, the Van Alstine plans or kit is one of the best deals going.

Dave

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David A. Mallett

Come taste muh' Klipsch!

This message has been edited by Mallett on 09-23-2002 at 11:08 AM

[edwardre]

KJ - I have the exact same setup you've just purchased. Have had both PAS and ST-70 for years in the garage collecting dust and like you, based upon rave reviews on this board, have decided to put it in service to see what the fuss is all about. My plan is to listen to 2-channel music (primarily CD's) with the tubes and reserve the HT experience for my SS. BTW - my HT receiver is also like your's, the Denon 3802.

The Dynaco setup was my fathers, so other than early life exposure, I really had no firm opinion compared to the Denon. About 2 months ago, after several self-induced setbacks, I finally got the vintage gear up and running. I am powering Khorns. My first impression is that the sound is very warm and full, without the 'treble-lacking' that the term 'warm' is usually associated with. Overall, I found the tube sound to be very engaging, to the point that it really didn't matter what the subject material was (to a point!), I just wanted to listen to it to hear the delicate harmonics and sonic 'blend' that I all the sudden realized was lacking from my Denon. This is not to put down the 3802. Prior to the 3802 I had a Denon 1701. The difference from that unit to the 3802 was very pronounced. I find the 3802 to be warm as compared to the older 1701, so the ST-70 was not a HUGE leap from the 3802. They are both rather similar in sound with the ST-70 taking 'warm and engaging' to the next plateau.

My tube nirvana lasted about a week then the ST70/PAS combo started to develop problems which I associated with extended periods of lethargy. Static, popping, and other distractions plagued the listening experience to the point of unbearable. I am currently in the midst of complete overhauls of both units, having experienced enough positives to warrant continuation of the pleasure tubes can bring. After gleaning tips from this BB, as well as surfing the net for info, I decided to first 'beef-up' the PAS. I have since replaced all the original caps with Sprague 'orange drops', which were available to me here at work for a song. I have also replaced the rear RCA Phono Jack connectors with updated ones (mine were really corroded). Resoldered most of the solder joints and of course, cleaned the pots. I am now 'burning-in' the caps by outputting to a Bryston 2-channel amp in the garage workbench area whilst I complete the ST-70 mods. I can tell you that replacing those aged caps as well as the few other tweeks made a tremendous difference in response. Bass is tighter and sound 'recovery' is much more quick. Additionally, there are no more pops and scratches. It appears to now be reliable.

WRT the ST70, I'm smack-dab in the middle of applying the Van Alstine DIY mod detailed on their website referring to the '1982 Audio Basics Complete Rebuild Plans'. Additionally, I have likewise replaced the old Dynaco-labeled caps with Spragues and have replaced the input jacks and output terminal strips. I am eagerly awaiting completion so I can really test this guy!

From all the input I've received, we have a very highly regarded 'tube introductory system' that is user upgradable. Seems to be a reason that the ST-70 has been around for so long. I think you'll be very pleased as even dead stock, the sound is perceptably better than the 3802. Have fun!

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Ed

[mobile homeless]

I am not sure whether I would say that the Dynaco ST-70 is the single most effective tube amp ever designed as it is really outclassed by others with better transformers not to mention better build. In stock form, it tends to have more soft and plump bass, not quite so extended highs, and not exactly the most see-through amp around. It is a very lush sounding amp and does have a good midrange. IT is surely one of the most popular amps ever built and widely available, and if this is what is meant by the most effective, I would agree.

Of the mods, I think the Welborne looks very compelling but it is very expensive. Both the Van Alstine and Welborne mods cost some serious ducats. Mods like the Triode Electronics board etc are more refinements of the circuit with better tube selection; he also sells a bias board.

You need to do your own research and ask some questions to various owners that have heard the different circuits. I have only heard a recapped ST-70 and most have only heard the mod they have chosen. Consider youself lucky that you have a friend gifted with the iron.

IF you havent seen it, this page offers some interesting summaries and thoughts - Please take a look and bookmark:

http://www.netaxs.com/~vkalia/st70-rebuild3.html

After you have looked at all the options, I would recommend hopping onto the Tube Asylum archives and doing some research on ST-70 mods where you will find all sorts of opinions and many posts, several from people that have done more than one. IE:

http://db.audioasylum.com/cgi/m.pl?forum=tubes&n=69724&highlight=Van+Alstine+ST-70& session=

The ST-70 is surely not the be-all end-all tube amp. It has weaknesses and some of the faults that many attribute to mediocre tube sonics. Then again, it also has some of the magic. I personally prefer other options but now that you have the beasts, you can get a taste of the entry point into tube sound. Just dont judge all tube audio from this circuit.

Part of the fun is doing all the research and learning a great deal. Like our shared world of the indie hell hole, there are all sorts of levels of involvment. It just might start you to where you will never return, just like the music did (can you ever listen to normal FM radio the same? heh...).

You might want to just get the Triode Electronics board and rebuild the pieces (take a look at the other options on that site too). IT will get your feet wet and perhaps ready to move on to more compelling options.

kh

Phono Linn Sondek LP-12 Valhalla / Linn Basic Plus / Sumiko Blue Point

CD Player Rega Planet

Preamp Cary Audio SLP-70 w/Phono Modified

Amplifier Welborne Labs 2A3 Moondog Monoblocks

Cable DIYCable Superlative / Twisted Cross Connect

Speaker 1977 Klipsch Cornwall I w/Alnico & Type B Crossover

Links system one online / alternate components / Asylum Listing f>s>

This message has been edited by mobile homeless on 09-23-2002 at 01:03 PM

[Mallette]

"...if this is what is meant by the most effective, I would agree."

That is what I meant.

Dave

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David A. Mallett

Come taste muh' Klipsch!

[kjohnsonhp]

What are the other options...or "more compelling options"? In vintage I've read a lot about the EICO 81 and some about Scott and Fischer but I'm not sure what would be a good alternative to the Dynaco ST70 and round out a sampling of sub $1k vintage gear. I was looking at the EICO but they seem to be selling high at the moment (but maybe dropping). In new The Moondogs seem to be the fav but at about $1500...I thought I'd start with some vintage testing and work up.

I need more shopping & research patience and I need to start with a less expensive base unit if I'm going to do a lot of mods.

I'll probably just do minor work on this first unit--triode board (~$80)?--we were initially just thinking of swapping out the old caps, replacing tubes as needed and cleaning it up.

Thanks for all the opinions. My wife's opinion is that I should go to a store and buy a complete setup and get back to the rest of my life.

I posted a pic of some of my favorite Boston indie bands from college on the Indie Rock thread.

[NOSValves]

kjohnsonhp,

Since you bought these unit I suggest you drop MDeneen a email asking his advise he has modded tons of Dynaco amps and really knows what there capable of he's been real busy lately so I think a email and patience might net you some good idea's. Here's his email address email . He's a great guy helpfull and patient but real busy most of the time.

He think very highly of the ST-70. But thinks it needs various mods to strut it stuff so to speak. I'd like to get one some day and tinker with it.

Craig

By the way you scored a heck of a deal on them too ! I paid 125.00 for a Pas 3 alone !! Those amp usually go for $350

This message has been edited by NOS440 on 09-23-2002 at 06:04 PM