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OFF - FOR SALE: Dynaco VTA ST-70 stereo tube amplifier

Item #649258208
Info: Dynaco VTA ST-70 stereo tube amplifier

Asking Price:
CAD $900.00
Payment method: Cash, Paypal
Shipping weight: 18.00 (kg) Calculate Shipping
Condition: 9 - Excellent (?)
Date Posted: Sep 16, 17 10:22am (PST)
Edited: Oct 13, 17 9:02pm
About Seller: ON, Canada
Days in System:90

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Selling this along with my analog gear.. I built this one about 2 years ago and has been working flawlessly since then. This one has low hours as I find myself listen to my SET amp most of time..

As this amp is very heavy and I don't have the box for it, prefer local sale, but I can ship it providing buyer pay the shipping cost..

Coming with all the tubes:
4 Tunsol 6L6G
1 Sovtek 5AR4
2 JJ ECC82

Various upgrades I put in:
ClarityCap ESA and Obbligato Gold Premium coupling caps
Nichicon low ESR power supply caps
Time Delay Relay, the time delay allows the tube filament heaters to come up before any high voltage is applied, this gives your tube long and happy life..

Brand new amp will cost you around CAN$1900.. http://www.tubes4hifi.com/bob.htm#ST70

VTA Stereo 70 from USING ALL NEW parts. There are no "recycled parts" from an original Dynaco ST-70. Now you can BUILD YOUR OWN ST-70 on a new type 304 STAINLESS STEEL CHASSIS FRAME with stainless steel hardware. Although looking near stock, this ST-70 KIT has several upgrades which make it a more reliable and much better sounding amp.

1. The new 16 gauge STAINLESS STEEL chassis is identical in size, shape and markings to the older original nickel plated steel frame except it weighs 1.25 pounds more than the original Dynaco 18 gauge chassis. This upgraded chassis is NON-MAGNETIC and removes any magnetic interference effects of a steel chassis on the audio circuitry. 16 gauge stainless steel bottom cover with four hard rubber chassis supports also included.

2. The new power transformer has a 5/8 inch higher stack lamination and is rated for 120 volts instead of 115 like the old design. The two tube heater legs are rated for 5 amps each instead of 3 amps each like the old design. This beefed up transformer allows the use of 6L6, KT66, KT77, KT88 or 6550 output tubes in place of the standard EL34 tubes for a slightly different tonal presentation.The transformer sits on 4 neoprene isolation mounts to prevent any mechanically generated transformer noise from entering the chassis.

3. The A-470 output transformers are brand new USA made custom production transformers. They use the same interleaved/layer winding technique as the original Dynaco cloth lead A-470's and incorporate high quality silicon steel M-6 grain oriented laminations. They are dimensionally accurate to the original design, come with a black oxide finish and have 4, 8 and 16 ohm secondaries.

4. The old stock 30, 20, 20, 20 electrolytic quad cap (90 Mfd total) which had marginal storage capacity for this amp has been replaced by a 80, 40, 30, 20 quad cap for almost double the power storage capacity. In conjunction with the 88 Mfd to power the driver board this amp has 258 Mfd of power storage - almost 3 times what the old amp had.

5. The upgraded VTA driver board uses three 12AU7 (or 12BH7 or 6189 or 5963 or 5814) triodes in place of the two mediocre sounding 7199 pentode/triode tubes. Dynaco saved money using a two tube 7199 board design but made some serious compromises in sound quality. The VTA triple triode board, however, features a better phase splitter/inverter design with CCS (constant current source). The VTA driver also uses less feedback for noticeably better sound than the old design. No more soggy bass and rolled off top end. The older ST-70 design had one bias control for each channel whereas the VTA board has a separate bias control for each of the four output tubes. This design allows for individual adjustment of each output tube bias. Matched pairs or quads of output tubes are not necessary with this design.

6. The input jacks are gold plated and have a wider (9/16 of an inch) spacing to allow for newer design thicker interconnects. The original Dynaco input board had a 3/8 inch spacing and most replacement ST-70 input mounting boards have a 1/2 inch spacing. (see photo)

7. The output jacks are modern gold plated 5 way binding posts. They may be set up for 4, 8 or 16 ohm speakers.

8. The 7 octal tube sockets are high quality Celanex sockets. These sockets are very durable and more reliable than the older stock phenolic tube sockets found in the original amps.

9. Also includes triode/pentode switches to allow a quick change between these two modes of operation. The switching may be done while the amp is running to instantly compare the two sonic presentations.

The complete kit contains the following parts ...

1 - Assembly manual with pictorial and color photo
1 - 16 gauge Stainless Steel chassis frame with original Dynaco markings
1 - VTA CCS driver board and parts set
7 - Quality Celanex octal tube sockets
1 - USA made PA-060 power transformer with bottom plate
4 - hard rubber isolation washers for power transformer
2 - USA made A-470 output transformers
1 - C24-X 240 milliamp choke
1 - multi section (80, 40, 30, 20) quadruple electrolytic capacitor
1 - three lug terminal strip
6 - grounding lugs
1 - pair of gold plated RCA input jack jacks with mounting board
2 - pair of gold plated output binding posts with mounting board
1 - rubber grommet
1 - fuse post with 3 amp SLO-BLO fuse
2 - SPST 11 amp rated slide switches
1 - 13 amp rated AC power cord
2 - .022 Mfd 100 volt capacitors
4 - 1000 ohm 1 watt resistors
4 - 10 ohm 1 % 2 watt bias resistors
1 - 2200 ohm 2 watt resistor for quad cap
1 - hardware kit for amp with all stainless steel screws
1 - 22 foot coil of 20 gauge tinned solid core copper wire
2 - Triode/ultralinear switches with associated parts

FAQ on the ST-70 tube amp kit ...

1. Will the standard ST-70 tube cage from my original ST-70 amp fit your chassis?
Yes - Since this chassis is identical to the original chassis except made of stainless steel, your original ST-70 tube cage will fit this ST-70 kit amp.

2. I live in Europe which has 240 volt AC voltage. Do you have a 240 volt transformer for your ST-70 ?
Yes, there is an optional 120/240 dual primary power transformer available for the ST-70 kit for our worldwide customers which is +$35. The amp may be also operated in Europe with an external transformer drop device used for operating USA 120 volt AC devices on 240 volt AC European voltage. These external transformers, which are available online, should be capable of supplying 600 to 800 watts of power.

3. How do these Triode/ultralinear switches work ?
The normal mode of operation for the original Dynaco ST-70 was pentode/ultralinear. The two switches (one for each channel) allow the amp to be operated in either mode and may be switched "on the fly" with the amp running to instantly compare the two sonic presentations. Which mode is best for your system is largely dependent on your associated equipment and your listening tastes. A generalized comparison of the two modes is summarized below ...

Triode mode - Power is reduced to about 20 watts per channel. The amp will have a little more mid range projection with a very slight roll off of the extreme upper and lower frequencies. Nice for acoustic jazz, vocals and systems with an aggressive top end.

Pentode ultralinear mode -- The normal mode of operation for the ST-70. Full power of 35 watts per channel. The amp will have more output at the frequency extremes. Nice for bass shy systems and systems that are a little "dark" in their top end.

4. Why does your amp have two tube sockets on the front face of the amp?
The two tube sockets on the front were on the ORIGINAL Dynaco ST-70. They were used as power takeoff sockets because the original Dynaco tube preamps (the PAM-1) had no power supply and drew power from the amp through an umbilical cord that connected the preamp to the power amp. On my ST-70 amp these sockets are not used for any "power takeoff" but two pins on each socket are used as bias measuring points for the output tubes. So these tube sockets still have a useful function on this amp.

5. I've heard that the Dynaco A-470 cloth lead output transformers on the original Dynaco ST-70's are some
of the best output transformers ever made. Are your output transformers as good as the originals?
Statements like this continue to float around the internet. What people really mean is that in the fairly
mediocre parts set that the original Dynaco ST-70 amps were made from, the only items that were of very
good quality were the two A-470 output transformers. Understand also that it is not that difficult to
"reverse engineer" an output transformer. By simply unwinding an original transformer and noting the
core size, wire size, number of turns per winding and winding technique a transformer company can
"clone" an output transformer that looks like and (more importantly) sounds like an original Dynaco A-
470 output transformer.

6. Can this kit be purchased without a chassis? I want to design and use my own custom chassis ..
Sure ... Email me for details about purchasing the kit without a chassis ..

Specifications for the VTA ST-70 amp
Power output ................... 35 watts RMS per channel from 17 Hz to 30 KHz at less than 1% THD with both channels driven in PENTODE - 20 watts RMS in TRIODE.
IMD.................................. < .45% (19 Khz and 20 Khz) at rated power
Frequency response ....... 10 Hz to 30 KHz +/- .1 dB at 1 watt
Power bandwidth ............ 17 Hz to 30 KHz +/- .3 dB at 35 watts
Feedback .........................13 dB
Input impedance .............. 270,000 ohms
Damping factor ................ 16
Hum and noise ................ > 90 dB below 35 watt output
The ST-70 does not invert phase
Dimensions - 13.0" wide X 9.5" deep X 6.5" high
Weight - 32 pounds > shipping weight 37 pounds
Unsolicited Email comments below from ST-70 customers ...

Started up the VTA ST-70 this weekend. Amazing sound, I'm very satisfied with everything. Superb instructions, easy to follow. No hum whatsoever and great warm sound. It started up right away after your instructions on upstart and bias adjustment .... I am very pleased with this kit which gave me a lot of building pleasure and I'm sure I'll have many hours of listening pleasure in the future." J. L., Sweden

"Bob ....WOW, I am sitting here listening to some vintage Emerson, Lake and Palmer and Steely Dan AJA .. If this thing is going to sound better after some burn in -- I can hardly wait. The other two tube amps I have are supposed to be around 35 watts/channel -- they don't even come close to the dynamics I am getting out of this ST-70 right after initial start up. The imaging is holographic with vocals pinpoint where they should be near the center and specific instruments with pinpoint locations outside the speakers with some forward and some behind the speakers--truely a 3D image of what the music should sound like - and very S-M-O-O-T-H overall sounding. That said, the Bass is full, articulate and powerful like it should be. My 12 year old son even came in to hear the initial fireup and was so impressed with the sound he actually sat down and listened for a good half hour before returning to his video game (quite an accomplishment)." B. H., Nebraska

"Hey Bob, just a quick note to let you know that I got the amp all finished this weekend. I worked on it for a couple of hours once or twice a week for the last few weeks and finally got it done. It sounds great! I was really impressed! This is actually the first kit (out of about 20 that I have built) that the instructions were in such detail, that you didn't have to Guess where things went or what to do "if" somthing didn't fit. I didn't have one single problem. Excellent , Excellent, Excellent!! I have it outfitted with some JJ KT88's. I got it going, set the bias, let it run for about 10 minutes or so, rechecked, dialed them in a little more and had it on for about 3 hours. I checked them again and it was right where i had it! I was up last night until about 2:30 AM this morning listening to it. It sounds wonderful. The sound quality is much better than the Velleman kit that I put together. Thanks again! Glad I found you! Hope you have a great Holiday!" R. B., Florida

"Hi Bob, I purchased the VTA ST-70 and PIO caps a few months ago. I have to tell you I love it! The caps made a huge improvement in texture and detail. Added EH tubes and they (after breakin) made drums and bass have a punch that I never heard before. Great kit! Thanks for selling something so good and so affordable .." T. H. New Jersey

"Hi Bob,
Just wanted to let you know that I finished the amp last night. I plugged in the tubes, made the bias adjustments and it worked first shot. The instructions were great. I really enjoyed building this amp. Now I'm looking to pickup a Dynaco pre-amp and maybe updating it with new parts to go along with my power amp." B. B., New Hampshire

"Bob: Just a note to let you know that the assembly of the amplifier went smoothly and it's working great. The sound is excellent. Even some CD's that sounded sterile and harsh on my NAD solid state amp now sound quite listenable. Setting the bias was a snap, got the bias for all tubes adjusted close to each other in just a few minutes. And I haven't even moved it from triode to pentode; the triode mode provides plenty of power to drive my Epos ELS-3 speakers. Great kit. I'm very happy with it." L. G., South Carolina

"Bob, The kit went together very well. Great directions ... The amp's sound quality, i.e. timbrel accuracy, imaging and sound stage, depth, etc. are all absolutely wonderful." J. M., Oregon

"Hey Bob ... I built a number of Heathkit, Eico and Dynakits back in the 1960's and 1970's but your kit far and away had the best assembly manual and the highest quality parts I have ever seen in an amp kit. An 11 amp rated power switch! Hey - the fuse blows at 3 amps! Beautiful stainless steel chassis. I love the triode/pentode switches. I haven't really decided which way sounds best because they both sound great .. Your amp sounds so much better than my old ST-70 .." C. W., Texas

"Bob, I just finished a weekend listening to the VTA ST-70 I purchase from you and which arrived on time last week. Having been an owner of two original Dynaco ST70's, I was not prepared for how much better your version is. It has the sweetness of the original but with sold lows, foot tapping rythm an much more accurate highs. I was so impressed that I am writing to you to inquire about availability of another unit, assembled and with the Russian caps ..." D. S., Puerto Rico (Note - Second amp was purchased on 2/25/08)

"Bob, What I am really surprised about is that this amp is so clear and lively.... it makes my solid state monos sound dull... the detail is fascinating and it does have that liquidy tube sound without being overly liquid. I very much like it so far and presume it will keep getting better for a while! I am impressed, really." J. C., Quebec, Canada

"Bob, Just wanted to send you a quick note to say I have completed your VTA ST-70 Amp and LOVE it! I am sitting here listening to my I-pod and cannot get over the incredible dynamic range of this little amp. Being more of a "tech" than an audiophile, I may not be an expert in sound reproduction, but this amp sounds great! Maybe its more the pride and satisfaction of having built it myself but in any case, I do appreciate the comprehensive instructions and quality parts you put into this kit. Thanks again!, S. B., Florida

"I was so impressed with the wonderful soundstage and the quality of the components of Bob's ST-70 that I sold the Conrad Johnson and bought another amp from Bob. I biamped my Tyler Acoustics Linbrook System II's ... The result was not surprising, because I expected great soundstage, enormous headspace and warm bass response which I more than got ..." R. W., Virginia > Biamping with two Dynaco ST-70's

"Bob, I've got the amp all together and running. It took me about 9 hours time to do the assembly. All of the parts were there. No missing parts. What can I say, Bob? This amp sounds terrific. Very, very musical. I can hear nuances in the music that I've never heard before! The high frequency responsing is towering! I was sitting there asking myself " What's that"?? "What's that"??? Great job on the amp!" M.B., Louisiana

"Bob, All I got to say is OH MY GOD!!!!! Not even through the break in period and the sound is exceptional! My friends can't believe the rich warm sound of Mantovani and the kick ass bass of AC DC! this amp ROCKS! This kit is amazing!" M. W., Florida

" ....my ST-70 replica is the best amp I've ever owned and one of the best I've ever heard. I love it. It has none of the weaknesses of the original. There are stories on the internet of people giving up $5,000 conrad-johnsons and Air Tights for this thing, and I believe them. Simply the most satisfying audio purchase of my life ..." M. J., Wisconsin

"Bob, Just a short one to let you know how I made out with the kit I recently bought from you. It took me about 10 hours to complete the assembly and testing and I must confess that I was very apprehensive the first time I threw the switch. To make a long story short it worked perfectly! I was very impressed with the quality of the sound ... The length of time for construction and confusion at times is probably due to the fact that I will be observing my 81st birthday in April. Not bad for an old man!" C. J. New Jersey

"Hi Bob, Well, around 40 hours on the amp since I completed the build. Absolutely beautiful pure warm clean amplification. The quality of the components you sourced is exceptional and the kit impeccable. Even my beautiful wife remarked " you know that stereo you built sounds a lot better then the one in the living room (Denon)... " She is right of course. Thanks again for the excellent product." R. L., California

"I made a post about speakers a while ago and my Tannoys being "bright" or harsh on the top end. I plugged in the VTA ST-70 amp, nothing exploded, I plugged in the output tubes, nothing got fried, I set all the bias values, then switched the cables out of my Cinema Grand into the 70. At first I thought something was very wrong, because I was SURE I unplugged my subwoofer (I listened to the Tannoys first without and with the subwoofer), but something was wrong. The little VTA 70 had MORE bass??? No way, I got up and made sure the sub was unplugged. Yup. After flipping through some very familiar music, I can tell you that YES, you can hear a difference with tubes (sorry for my exhuberance this is my first tube amp.) I am stunned by the warmth and how my Tannoys are suddenly better. But, it gets even better. I had it in pentode mode. I flipped to triode mode, and it got a bit quieter, and my somewhat bright Tannoys now are totally different speakers. My symphonic music is better, Dean Martin's Christmas disc suddenly has a real upright bass player where I can visualize the slap of the bass player on the strings. If you'll excuse me, I have about 3,500 CD's that need to be listened to again. The kicker is this: my 10 year old daughter, who doesn't care about anything I really care about, walked into the living room and asked if I got new speakers because my stereo sounded better. When I told her Daddy built it, she asked who I had help me. I should be happy she noticed it." A. S., New York

The sound? Wonderful. I was listening particularly closely to Ricky Lee Jones' Naked Songs, and noticed a fuller sound, with certainly more bass. There was a ... gentleness, or softness to the sound, which I believe to be a characteristic of tubes, yet there was definitely more detail than the Naim. I was sure I was hearing things I hadn't heard before, and ... I'm not just hearing things. ;-) It seemed to me that some of her guitar chords had additional notes/strings in there I hadn't noticed before. I'm sure of it because I was surprised by the additional notes in there. This VTA version of the Dynaco ST-70 amp is a phenomenal value for money. It's a great looking piece. Dynaco is a legend, yet this thing is a modern anachronism. It just tickles me to death that a 50 year old design has been able to be modified and upgraded so that it can sound so good. The instructions were clear and easy to follow. I haven't touched a soldering iron since the 80's. I think anyone who can learn to tie their own shoelaces can build this amp, learn a few valuable, transferable lessons, and save themselves a pile of dough considering what they have at the end. B. C. Calgary, Canada


Audio Asylum review #1 of the ST-70 kit


Audio Asylum review #2 of the ST-70 kit - from a FIRST TIME KIT BUILDER


Audio Asylum review #3 of the ST-70 kit


Audio Asylum review #4 of the ST-70 kit


Audio Asylum review #5 of the ST-70 kit


A custom VTA ST-70 amp build


Comparison - an original ST-70 and the VTA ST-70


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