Dynaco St-70 Vacuum Tube Power Amplifier. One Of The Best Vintage Stereo Components Of All Time.
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- เผยแพร่เมื่อ 28 ม.ค. 2021
- This video shows the restoration, repair, and testing of the Dynaco ST-70 stereo power amplifier. One of the most copied amplifier designs in history and it was developed in the 1950's! An amazing piece of audio history.
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I got mine in 2012 from a dumpster parked in front of a home being cleared out by heirs. It needed repairs. It is my most treasured piece of audio equipment. Distortion from it is now is so low it is no longer measurable on my THD meter. I love it. Lots of under the chassis mods of my own making. It has it's beautiful table to sit on and spot lights in the ceiling set it off. A treasure that I expect will show up in my own estate and I hope someone else finds it and loves it.
Thanks for the trip down memory lane! Great amp, great video. My uncle built a Dynakit 70 in 1964 right after he was married. (He happened to build it in the same little cottage I was born in 4 years prior, and I remember seeing all the parts spread out on the table....just about eye height for me then) He gave that amp to me in the late 80s, and is still in use today. I had no idea then that my system would get built around that amp.
Shortly after acquiring the Dynakit 70, a factory wired Dynaco 70 showed up in the local swap sheet for $50, so I picked up a 2nd unit. Only one channel of the factory wired model worked, so I swapped around some tubes between the two amps so that each amp had one working channel with the same tubes, and I ran them as single channel monoblocks for a while. A friend added more capacitance to the power supplies, and wired the the EL34s in triode mode for me. I thought they sounded wonderful and ran those for a good long time before adding the Bob Latino VTA boards (tubes4hifi) in 2020. A couple years later I removed the rectifier tubes and added Roy Mottram's copper body solid state rectifier, and installed new Tung Sol 7581A outputs (in triode), and 12BH7a driver tubes. Wow, what an incredible set of amplifiers!
Bass was a bit punchier, but still not dominant the way a good solid state amp is on the bottom end, so still not quite finished, I added an active low pass filter @ 80hz, and threw a vintage Kenwood integrated into the mix to power just the woofers of my transmission line speakers, and ran the Dyna monoblocks to the midbass and tweeters. Sort of a hybrid bi-amp configuration. My ship has come in! Sunglasses on, beer in hand, smile on my face, and favorite tunes shuffling in the CD player, I don't think I could be happier with these 60+ year old amplifiers, but I do occasionally pull out an LP and take things to another level. I can't imagine what I'd have to spend to get better sounding amps! Absolutely love these!
68 year old Boomer here - this was the rig Pops built in '60; bought the Dynakit from Allied Audio in Chicago where he was a designer for Sears. He built the PAS matching pre-amp too. From Knight Audio came the modern big oiled walnut cabinets about 5 of 'em on a huge frame - two were for the speakers and the rest were for books or storage-very Playboy. The speakers ran at 4ohms and were EV woojers with freaking HORN tweeters. Funny I was 6-7 and remember this like yesterday. That system played the NEW "stereo" demonstration records - Jazz from Command etc... Took me from the Twist thru the Beatles and Rock before I moved out. That thing made me the envy of all my friends in the 60s because nobody had separate component stereos yet with the Garrard or Dual turntable and man that thing was LOUD. Cream's wheels of fire at about 12:30 on the dial got complaints from a mile away. Jazz and Classical sparkled.
Thanks for posting this - I was just going down memory lane and thought I wonder if anybody's heard of a Dynaco - they kicked ASS WAAAY before anybody heard stuff from Pioneer, Sansui, Scott, Fisher, marantz, Macintosh, etc..... ⏚🎶
Thanks so much for sharing. Great story! This equipment brings back great memories for me also.
@@vintageaudioaddict Hey man, I'm just a passenger - you're the Bus driver; Thanks again ! 🎹
Just picked one of these up for 50 bucks in great condition, can't wait to hook it up to my totem acoustic dreamcatchers... Should be a banging little setup
Thanks for the video. I am always pleased to see these old amps still doing the job they were designed for. Funny thing, I was coming home from school one day back in 1974 when I came across a home made console some one threw out and being a electronics tech, I looked inside. Speakers were old and cones trashed ( 15 and horn from a Magnovox ) but right there in the center was the DYNAKIT ST70. I had nothing but my books with me and a pocket knife. So,I went to work digging out that Amp. Got it home and it worked. Loved it. Never parted with it, still have it today and it still works. ( retubed 1 time ).
Your right about the sound. I am a musician and I have a recoding studio. ( Home style ) I was curious one day and used the ST70 to drive my JBL monitors ( I was using a Bose 1801 ) and yes, it actually sounded smoother than the Bose power amp. I had a turn table hooked up and played quite a few records with it on the monitors and a laughed all the way throgh it. Dam, it had that smooth sweet sound almost made things more real than the bose.
All in all, I agree, these were ahead of their time and I also agree with the saying: this is the Poor Mans Mac.
Wow! This brings back memories! When I was in college in the early 70's I had a dyna kit 70 amp and pre amp, a pair of EPI 100 speakers and a BSR turntable. After college I sold it to a friend who still has it today.
Very Cool! This equipment brings back some great memories for folks. Including me!
My dad had one. Kit version. Also preamp and Tuner. Great sound. Could drive it quit hard. Worked into 1990's. Wish I still had it. Could almost heat the whole basement with it.
I am listening to this through an ST-70.
Very Cool!
Me too! This amp was born the same year as me :) I'm using JJ KT 77 and a Mullard GZ34 rectifier, fed by an Audio Research LS27 to vintage Altec Model 19's, Glorious!
I bought / built one in 1964 - in High School. Worked 1st time I turned it on !! Wish I still had it. It was a great amp - and served me well all thru high school and college !!
Very cool! Thanks so much for sharing.
Born in 54. I’ve always wanted one of those Dynaco amps. In college i used to go to the local hi-fi store and look and listen to them. Could not afford one back then. If you ever think of selling it let me know by replying to this. Great video.
Thanks for watching. I haven't sold any of the equipment in my collection yet but I'm not getting any younger.
I've owned a Stereo 70 and PAS3 since the mid-60's, and finally had to start replacing parts about 5 years ago. Basically, these are excellent hi-fi components, and compare well with modern stuff I've owned. I think I'm going to keep this set forever.
I had two of those beautiful amps for safety reasons I left them in Mexico but I was able to recover an Eico Tube pre amplifier I'm so glad I did.
Very nice!
Thoroughly enjoy your videos and learn from your comments and suggestions.Keep em coming!! John K
I had 2 ST-70s! Got them at garage sales for $5.00 in the early 80's! They've served me well since!
Man, great deal!
@Christiaan Baron Sadly, I tossed both sets of ST-70s, PAS-3s & FM-1s I had when I moved from Los Angeles to Palm Springs a few years ago.
Great review, hearing your passion for the ST-70 in a level-headed and realistic way was great to see and hear. I’ll be picking one up in the next day or so, and I’ve been looking forward to it for a long time. This video had me pumped up for things on the horizon.
Thanks so much! I think that you'll really like your ST-70.
@@vintageaudioaddict I will report back ... picking up Saturday morning. This particular unit has Gold Lion KT88's and other various 'upgrades' ... the Bob Latino version ... fully done up. I have a tube pre-amp ... but only solid state amplifiers at this point ... this is a first for me.
Yes! More good stuff from this channel. I dont have one of these, and probably never will. Still well worth the view.
Thanks for watching!
@@vintageaudioaddict this channel gave me a few nuggets of wisdom to consider while shopping around for a classic stereo receiver. I found a nice Marantz 1550 and i couldnt be happier.
Love your channel as I am wanting to get back into the hobby. I too am a baby boomer born in 1959. In the early 70's while visiting family in north texas we stumbled upon a pawn shop with some classic Macintosh equipment. A C20 preamp and two mc30 mono Amps all for $100. Had some upgrades done by the local shop tech. Unfortunately that equipment was stolen while I was overseas in the Marines.
Thank you so much for your kind words. Thank you also for sharing your story and for your service! Great deal on the McIntosh gear but I'm sorry you lost them.
I'm on my second Dynaco now. I totally rebuilt.y first one before I'd ever heard one! Got this one pretty much stock, some caps were upgraded otherwise all original ! Love your videos !
Thanks so much for the kind words and for watching. Dynaco made some great gear back in the day.
Thanks Again ! I see these amps for sale all the time
You bet!
sir i have a 70 and p pas pre amp love them purchaged for 50$ years ago.terrific video you spoke truths .thank you.
Thank you so much
Enjoyed many st70’s, mk iii’s and a wonderful pair of Sound Valve mk iv’s in triode w premium parts on Stax cans, truly sublime!
Thanks for sharing!
I have that exact same combo of the ST70 and the Macintosh 110 preamp. It is wonderful system with such detail and warmth, a real pleasure. Combined with my Totem speakers and Velodyne sub, even people who never listen to music other than their cell phone are amazed what real music can sound like.
Couldn't agree more! Thanks for sharing!
had a lot of Dynaco equipment in my life ,it was all great stuff.
Yes, Dynaco made some wonderful audio gear.
I'm new to your channel and own a lot of vintage tube amps of every type. I have a ton of Dynaco St70s and MK3s and I sold my only ST35 but I do have three SCA-35s and I can turn one of those into an ST35 very easily. I was shocked when you said 350k ST-70s were made as I always thought it was 200k but you were right or at least close. This is from Stereophile.
Back to the future. When Radial Engineering announced its plans to market a modern version of the Dynaco Stereo 70, the news struck me as a valiant time shift, aimed squarely at resurrecting the soul of one of the most influential amps of all time, and the component that enshrined Dynaco in audio’s Hall of Fame. Over a span of nearly 20 years in the 1960s and 70s, more than 400,000 ST-70s were sold both in kit and assembled forms, total sales by some estimates approaching half a million by 1977. That would make the ST-70 the most popular tube amplifier of all time. It sold well not only in the U.S. but also in Europe and Japan. I would venture to say that nearly every serious audiophile owned an ST-70 at some point in his lifetime.
Thanks for commenting and for sharing your knowledge.
No ST-70 but a ST-35. Love that little amp.
Yes, I have a ST-35 also. Great amp!
Great upload,very interesting amplifier Thanks ;)
Your welcome and thank you for watching.
Great video! Thanks
Dynaco tube amps have that golden honey-kissed midrange that's difficult to not love
I like it very much, the videos and the ST-70. Congratulations from Portugal.
Thank you very much! Cheers from the USA!
Stereo 70() by Dynaco 😂🎉
Beautiful piece!
Thank you very much!
The real, true, 'unknown designer' was the late Charles R. Worsham, Sr. I worked for his private radio company after he left Bendix radio in Towson, MD. His specialty was designing Linear Radio Frequency Amplifiers for the military. What he did at Bendix was more like 70 Kilowatts and 20 Megahertz, the 70 watts and 20Khz audio linear amplifier was contract job he did at night. Contact his widow, Lee Worsham, ask her, "Mrs. Worsham, what was your usband doing the night before his first son was born in 1959. He showed me where Dynaco had 'shortcut' the power stage by refusing to properly balance the output stage properly, and how to restore his original design on my factory edition Stereo 70. I grew up on vacuum tubes tubes in the early 1970's, when electronics was still taught in high school for free. But I am 68 now, and infirm. I am looking for a partner to rebuild/restore and upgrade this amp "world class"-- money is not my motive: fame is. I will handle the power supply and power amplifiers (matched EL34's was one of Dynaco's 'short cuts' to save on a few cheap passive components (jerks!).Even then, Worsham's genius is dominable. Mine works, and is disassembled. Worsham marked up my factory schematic to show how to correct the 'Dynaco deficiencies' (also cheap-skating the power supply by failing to use the proper filter for the job---but what the hell, it worked, and made them famous!
John Stegman (stegman.us -- personal web site)
Thanks for the video....50's and 60's the Golden Era of Tubes...DIY goes to HH Scott with LK and LT series. The Yoda goes to Marantz 8B, 7C. I am glad you can still purchase high quality DIY kits...Bob Latino VTA ST-70 or ST-120, Sunvalley and Elekit kits. Just ordered Sunvalley SV-Pre1616D Line Amp (cricut based on line stage of Marantz 7C)...There SV-EQ1616D Phono Amp (also DIY) is fantastic.
Your welcome and thanks so much for sharing.
I bought a kit back in the day , unfortunately I sold it , I’ve had few more , and still have one today , I also built ARC rebuild kit years ago & built that also , fun amps
Yes, they are great amps. I think it's amazing that something that was designed in the 1950's can still sound good today.
So, I decided to setup an old Analog record player with my Bose 901's but really wanted a tube amplifier. Asked my boss if he had one laying around and sure enough, he had a Dynaco ST-70 and a Pre-Amp in boxes in clean storage. Just got it home and it's pristine but I'll check it out and make sure it looks good internally before turning it up. Pretty excited. :-) Nice, vid, gives me some good advice on what to look for.
Congrats on your new gear! Every time I get something new I can't wait either. I'm sure that you will love you ST-70.
I've owned and modified more than one years ago. The main problem was the input board with the 7199 pentodes. However, many replacement boards have been designed that used triodes such as 12AU7s and better signal path caps. Solid state rectification and voltage regulation are a plus.
Great video very informative ! I too have a ST 70 . was helping an old timer organize his garage, and towards the tail end of two days helping , I found an old Cutty Shark Liquor box with a Dynaco St70 , a Dynaco FM Tuner & a PAS 2 Pre amp . At the time I did not know what this was, I asked him what would you like me to do with this? He replied either put it at the curb for the garbage man or take it to goodwill. I stared at him with my eyes wide open 😮 , Then he said unless …you want it ? To make a long story short I brought it home and had it fully restored . That was about 12 years ago . A question I have to everyone reading this , Other than the JJ power tubes & the JJ GZ34 / 5AR4 rectifier tube , What would you recommend that is reasonably priced , And where to buy tubes TODAY ( ASAP ) 1/15/23 .. Thanks in advance to everyone’s response !
I'm late to the party, but which tubes we like best is really subjective. I tried and liked the EH EL34s, and they were fairly affordable at the time. Haven't tried them yet, but am hearing some good feedback on the Psvanes. For anyone with the VTA mods, the Gold Lion KT66 is excellent, as is the Tung Sol 7581A. Would like to try a KT77 as some point, but even the affordable ones are now fairly expensive for the sake of playing.
If I recall, I think the original is one of Hafler's design. Great amp, I modded mine a bit -- extra B+ capacitance board, stepped volume control and SS rectifier. It really opens up the head room and gives it more dynamic power.
Thanks for the info!
I like seeing guys that do not use cheap JJ tubes.
Nice to see, I have renovated some ST 70 and also little brother ST 35 it is usually so that they are as close to original condition as the owners want them. I became very fond of ST 35 and got one for about $ 3 but according to the owner it had never worked well. I tore it down into parts and found the fault one of the high voltage cables was pinched under a transformer the main transformer measured and it was okay even OPT was. Built it together with new parts as I did not know if the components were ok. Today it drives a pair of Altec Lansing 604 E maybe a little too much power but what does it do.
Thanks so much for sharing. I have a ST-35 in my collection also. I hopefully can do a video on it someday. It's a great little amp!
Liked this
Thanks
I had one, wish I still had it. I still have the Dynaco A-25 speakers
I know what you mean. I've had gear in the past that I traded or sold and wished later I hadn't.
Sweeeeet. So retro...so much character
Thank you!
Another great video! Classic tube amp, I got the SCA-35 with the FM-3 tuner
Thank you again!
I will always regret trading in in my sca 35 for the pat 4 and Stereo 120. Really did not need all that extra power.
Loved your video. I have one on the bench now going to put in a new front end board. How do you polish and clean old metal?
Thanks! Use the least abrasive cleaner first. Warm water and little dish soap will go a long way but watch the stenciling on the chassis as it can come off if your not careful.
I am planning on building a modern version off of Bob Latino's site. Custom chassis, etc. Just have to find the time.
Cool project! Good luck!
For those looking at ST-70...Latino's update all day long as to beefed up parts, soft starts and more.
Tell me if you find time I have several things I should do
re: 2:25 : No those are not the original capacitors in it. Those photos show a lot of capacitors and resistors have been changed. But fun video regardless!
Thanks
Great Video! I have an old Hafler DH200 which I heard was a clone of a Dynaco SS amp. I just had an internal fuse blow on my amp and am curious if it is worth upgrading with new parts or consider new amplifiers?
Well hafler helped design the st-70 and became famous with his Rockford fosgate amplifiers in the 80-90s some of the best car amplifiers ever made
Please do more tube stuff
Will do
I love the look of these and compare to a pair of mono Macintosh 275, it is a bargain :) I am really a newbie to all of this, from all the different tube amps out there, how would this stack up against all others in terms of music quality or sound? Trying to get my feet wet
This is a beautiful amplifier. Did you ever find out why the power cable had been cut?
Thank you. No, the guy I purchased the ST-70 from had it around for years and he couldn't remember what had happened to it.
What was the sound track you used?
I had a Dynaco PAT5 and 120 power amp many years ago. Sold both of 'em while in college. Big Mistake. Now there are internet "re-build" shrines for Dynaco equipment. I did purchase an ST-70 type case for my "hackintosh" DIY class-D amp. Added a bright orange LED to get that tube-like glow...:)
Thanks for sharing.
I retrieved from my family's old residence my mother's stereo system. She had this Dynakit ST-70 paired with a Dyna Preamp PAS 3x. I'm now familiarizing myself with the 2. I am from the Philippines where our electric voltage is mostly 220v but in old residences, there was also the option of a 110v output. The pre-amp has an option for the 2 voltage sources but the ST-70 has nothing indicated on it. Since it's US built, I'm assuming it runs at 110v. Am I correct?
Yes, it was built for 117VAC nominal. You need a fairly hefty step up transformer, say 250VA, which NB is a power rating, not a voltage rating.
I think the Dynaco PAS-3/3X was the most modded piece of stereo equipment of all time, followed closely by the Dynaco Stereo-70. Lord knows I've repaired and modded enough of them since the early 70s.
Thanks for sharing.
Any reference or instructional manuals you would recommend to someone wanting to enjoy the hobby. Thanks in advance.
I have never seen any specific books or manuals about vintage audio in general. There is a lot of information in different places on the internet about the hobby but not just one site has everything.
Yup! :-)
I’m using my HHscott 222c restored
Yes ! >__< NAD 3020 integrated power amplifier sold over half a million units 3 months after its initial release.
Thanks for the info!
Why does it sound so good? The ultra-linear output transformer design probably has a lot to do with that. There is a low-end bass problem. Frank Van Alstine recommends a bass roll-off filter to raise the bass cutoff frequency a little. The amp is fine but the power supply can not keep up with the amp current demand at extreme low frequencies. You can find the info and more about the Stereo 70 by searching in the old magazine archives. Audio Basics avahifi.com/pages/audio-basics-newsletters Have fun. James
Thanks for commenting.
@@vintageaudioaddict You are very welcome.
Very informative. Thank you. One suggestion: On your next video, please let viewers hear the sound of the music without having yo navigate the sound of your voice talking OVER the music. I would have loved even 15-20 seconds of savoring the output of this amplifier. The music itself. No explanation needed.
Noted. Thanks for watching!
What did the underside look like after you worked on it?
Not much different really. I cleaned it up, replaced the wires that were held together with electrical tape and repaired the artwork where needed.
A foolish question. Are the valves still available? I mean easily?
Yes, they are still available. Mostly Russian and Chinese made. The OEM tubes are no longer manufactured but are still available on eBay etc. They are expensive.
@@vintageaudioaddict thanks
are 7199's similar to a 12AX7?
I inherited lots of tube equipment, including this same amp, and many amps and pre-amps, all "tubers". Obviously, you repair all sorts of sound equipment but where can I get these units repaired without being ripped off or told they are worthless?
Google "vintage audio repair" and see what comes up in your area. Keep in mind that any good technician is going to charge you to repair or restore the equipment. A person that can work on this equipment is no different then having a professional plumber or electrician come to your house. What would that cost you? A lot of folks think for $25 or $50 their piece of vintage audio equipment should be good to go. Rarely is that the case.
@@vintageaudioaddict I am not arguing that repair comes with a price. I just argue that there are too many claiming to do repairs that either do not know what they are doing or do more harm than good. I would just as soon leave what I have untouched sooner than have it repaired improperly. The thing I need to find out is who does the repairs properly.
i was born on 1972 and the BBC LS3/5A was born
EL34 tubes make great mid-range... Even in a PA amp.
Yes they do.
@@vintageaudioaddict
1958... Me too😊😊
NAD 3020 HOLDS THE RECORD .
Thanks for the info
From where I purchase in India
I really don't know but I'd google it.
The st70 is a class the design was straight out of the RCA rube guide the transfomer are all excellent as is the chassis big very easy too mod to use as long as you don’t drill holes the big lint on this is the quality of the components both caps and resistors if you do that all of your top end problems are gone the slam and powerful low end bi amp
Thanks for commenting
The ST-70 is class AB. It is similar to the RCA 30W amplifier from RC-30 1975, but which is not present in RC-16 1960, so you have the question of priority inverted. In any case there are significant differences, notably in using ultra-linear, which Hadler and Keroes thought they had invented.
Love everyone calling it an ST-70, it’s a Stereo 70, Dynaco never abbreviated the name. The ST-70 is a VTA reproduction amp.
Eico also made an ST-70 but it was an integrated amp.
rah rah rah
JJ tubes are junk cheap as you can buy the St-70 is a decent bit nothing crazy
Love mine
Dynaco Stereo 70 does not have the pomp of an Audio Research of Mcintosh amp, his humble aspect does not reflect the increible sound hidden inside of this amp.
Last week I change both 7199 tubes for 6gh8a tubes using an adapter.
Sounds amazing.
does a Mcintosh tube amp sound 5X better than a Dynaco? As I think they're 5X the price, my Dynaco very sweet highs, good mids, and No bass, can only use it in the winter, thank you
Thanks, great video!
You're welcome! Thanks for watching.