Very informative video. I never owned the original ST70, but, my first tube amp was from Panor, named the ST 70ll, memories of which I still use as fond references when doing vintage equipment comparisons to this day.
If there’s a problem with the cards is there a replacement path such as getting from a donor or are they available new from someone , or can be built ???
@@marklloyd4153 there is only one removable card in this unit. I believe someone has recreated the original design on a new PCB. Most boards can be salvaged though so it’s usually not an issue.
You did such a beautiful job no surprise . I know what you mean by the appearance of the incandescence lighting over the led but I think I would forgo the visual aspect of the lighting for the long life dependability of led for my own device I mean. I think that is great you can adapt the plugs in the back on the DB that are useless to do another task. I would like to be able to connect my Eversolo streamer DAC device to an old unit like this to bring the old and new together . I will look for one of these based on your under the hood explanation on why this is better than the DB
I’m so impressed with your work and how much you care about the end result and your customers being happy . I don’t c this behavior and attitude in many people in today’s world . Definitely look forward to dealing with you
Really incredible . I know very little of what you are doing but I love the end results . Do you sell these or repair them for people that send them in ???
What is shown on my channel is mostly personal pieces that I have restored for resale. I do work for local customers. I am not taking on ship in work at this time.
@@NovaluxStereophonic I can tell you are swamped with work like this . I’m not in any hurry I’m dealing with so many health issues as I was run over by an uninsured motorist . Learning to walk again . Would like to work with you on a few projects later hopefully . It would be such a joy to have 1 or 2 of these incredible pieces and to fix , repair and keep running for another 40 years for the next generation of enthusiasts that love these pieces. I love the new stuff too , but we wouldn’t have them without these pieces . I love seeing them improved on with led lighting that is soft . I like and have never seen the soft start applied in this way like on A/C units I’m more familiar with . I just keep learning but to know what you guys know I’d need another lifetime . So impressed
I love Rotel and Michi . I love what you get for the money . I have a new 1592 MKII . It drives 2 Polk R700s with the REL Classic subwoofer. It is connected to a Eversolo DMP A8 . I would love to have a few of these vintage . I like this Rotel . I love the pioneer 1250 , 1280s . I like the Realistic STA2100 . Toshiba SA7100 , sansui 9090 & G 8000 , marantz 2325 . They look so great . Is there one of these that has better mid ranges than the others ? I like miss and upper middle I like wide sound stages . Can someone help me?
This is very interesting to watch. I'm actually doing a Original and VTA upgrade of two heavily modded amps I picked up. I don't have the test equipment but looking forward to doing to listening comparison. I did order new larger power transformers and will put the rectifier diodes in on both. My vta will have the 6sn7's and the refreshed original board from soundvalves that uses the 6GH8. I wonder if the driver tubes is what may drive listener preference over the power tubes.
Excellent review. I was hoping for a commentary concerning the VTA's higher measured distortion and how it might correlate to what the listening panel heard. Maybe the sound level was not pushing the VTA amplifier, so the higher amount of distortion was not revealed.
i think the VTA board recomennds setting the output tube bias cooler than the stock original design. wich may be why the power and distortion are differant
I own one of these fitted with a Gracie G-840f tonearm. I put a Sumiko Moonstone on it. I cleaned it up and had it setup properly by a trusted audio shop. It sounds fantastic.
Greetings from Seattle. Incredible video! Yohu are te Model 9 genius. I have six of them, They have been worked on over the years, but no one of your caliber has worked on them. Obviously only the most skilled people should touch a Model 9. Do you offer repairs, restoration? Thanks!!
I'm pretty sure the disc platter and have something like a proprietary material that's not metal and it's not plastic it's like ceramic composite or something pretty sure I remember the literature 7000 Sony had something similar
Just Picked up A Sencore PA81. It has a right & Left channel VU intermittent pointer jumping thing going on. When you hit the meter select switch it will sometimes stick all the way to the right hand side, As you select from -60- to +40 and then -60 the pointer in the VU will stick to full scale right and sometimes just bob around for a second. You can hear very low static from the right speaker. If you give the side a light tap it will drop down and get quite. Sounds like something with a connectivity problem. If you jiggle the function switch it goes away .I'll have to go thru and check all connections. BTW Fantastic Video. I will be ordering those parts just incase.
@@maraeht these have issues with the relays after sitting for a long time. It may just resolve itself during normal use. The most common issues with these are faulty relays and broken switches for the monitor speaker controls.
Thanks for the reply just picked it up on my phone I'll get into it probably tomorrow fiddle around in there check the relays get out the old Kremlin D5 and start hunting really enjoyed your video and set up but I'm jealous because you have a full page sheets schematic schematic where can I get one of those I have PDF but they're a pain Patera paint to navigate but they're a pain to navigate love the way you put your video together keep up the great work regards mark
@@NovaluxStereophonic Did you take your schematic some where in PDF to get that Full size schematic you were using in your great Video? Several guys on my Sencore forum suggested Staples or a printer to make a one sheet full size for us old guys..L.O.L. Also they said that Adobe now has a service to make poster size anything. But it has to upload in .JPG. and you have to have the full Adobe program $$$$ which would convert PDF to .JPG. I just have the free Viewer. How did you get yours done? Thanks: Regards: Mark
Very interesting, thank you for this. I've had an ST-70 for years and always thought it sounded good (I've used it for bass and guitar as well as hi-fi), but frankly, I never knew its specs were so good numerically. One comment, for listening tests, it'd be interesting if you could involve some women as well; they seem to have very different hearing from men, as a general rule. Whenever I'm working with audio stuff, and particularly with my own playing and recording, I value the comments and observations of women: they frequently notice things and point out things which seem obvious once my attention is drawn to them, but which I hadn't been paying attention to before. Different perspectives.
Really enjoyed this video. Some great pointers. Was wondering if you you covered the Kenwood 700 M amp in a video? I have one along with the 700 C control amp and would love to see the restoration process!
I have the 700M video on my to do list but I have not gotten around to it yet. I am still searching for a non working 700C at the moment. I do have the 700T, the set is almost complete.
Great Video, I imagine you sold this unit some time ago. I have one, but as looking to locate a front panel board for it and was wondering if you might have any sources fro such a part? thx in advance, Blaise
I'm restoring a nice 5.5 and going to replace the stereo indicator with a red LED. The faceplates of these Concepts are very plain jane. I wish the meters could be backlit with their own LED. I would probably go with light blue.
I am a big fan of the VTA products. Built the VTA 120, updated with dual rectifiers and bias meters. The dual rectifier mod greatly improved reliability.
just amazing restoration. just a rank amateur here trying to remember some of what i used to know 40-50 years ago, and this kind of content is really fun to see. i've managed to repair a few solid state pieces (and blew up one stupidly). But enjoying the process. You're helping my confidence in getting ready to completely disassemble and restore an amp. Thanks!
Very interesting, I have a gut rebuilt ST-70 and I used quality and precision parts as well. But I don't think the VTA is really an ST-70, it is a completely different design and model It sounds to me that the VTA is enhancing (amplifying?) higher frequency but the tests show a similar frequency response. I have heard the 'missing" comment on my ST-70. What components would make this change in the sound of music? I guess this is the classical question for tube amp design. It almost sounds to me that there is an element of amp design that behaves differently based on the content of the music. Would an equalizer help to tune songs? (That would be a hassle!) What are your thoughts?
@@ToobTime the circuits vary in driver tubes, constant current source use, bias implementation, and negative feedback. I agree, very different amplifiers, the only thing common between them is the power and output transformers.
I'm not surprised by these results.....What surprises me is the fact that it has taken more than (20) + years before someone actually tested the VTA ST-70 upgrade circuit & compared this to the original David Hafler ST-70 design. Nice job Ben! Kevin D. from Dynakit
I recommend taking an interest in the B 2102 MOS VINTAGE model. Once upon a time I accidentally bought this model and it is still my best amplifier. even SX 1250 or 1280 performed poorly in comparison
Please change the feedback resistor on the vta70 board to something in the 5-5.7k range and retest it if possible. it would be very interesting to see if it fixes a lot of the issues that it had over the stock circuit or not. thanks.
Excellent. Loved watching this. Can you explain a little more about "marking the outside foil to minimize the noise floor" on the film caps? How do you do identify the foil side and does affect how the capacitor is installed?
If you do a search for “Mr. Carlson’s Lab outside foil” that should get you pointed in the right direction. He does a very good job of explaining it. The process involves testing and marking each cap and then installing them in the proper orientation to effectively make the outside foil of the cap act as a shield. It’s not 100% necessary but on tube gear I try to go the extra mile to keep noise / hum as low as possible.
@@NovaluxStereophonic Thanks for the reply. I've seen that video. Mr. Carlson's Lab is very informative and thorough. Sounds (kind of a pun) like a good idea. Can this be done accurately/reliably without an oscilloscope?
@@stevenjackson8226If you are interested in his circuits consider subscribing to his patreon page. For the circuit he shows on RU-vid and oscilloscope is needed.
Fun. Thanks for this. Great stuff. I've had lots of experience with Dynaco gear. Lots. And I've been tracking the conversation around Dynaco gear for a long time. I still have my father's ST-70, PAS-2, and FM-1/FM-3. Quick question. Is the stock 70 in the test using it's selenium rectifier? I didn't see it in the tour of the undersides of the amplifier. The feedback debate... good? bad? the debate continues??
Great vid.. I wish you had the Uprated Power Transformers for both amps. It runs cooler and makes a big difference, at least subjectively/sonically.. I have a not so common aftermarket Dynamutt Octal 6SL7input>6SN7PIBoard on my ST70.. And the the B+ supply caps (2 of them) are polypropyene, the other two are dual-section lytics (top mount) with small polyprop bypasses.. The Feedback R is user replaceable, with value recomendations for the Dynamutt board (basically a Mullard circuit with discrete solid state CCS on the PI 6SN7 cathodes - for forced balance) I chose the low FB setting since my speakers are not too hard to drive.. I’ve listened to a really souped up VTA and it projects a holographic image while retaining that El34 mellow tone.. Try replacing those stock metal films with tightly matched Allen-Bradley CC for the grids and plates.. Then do the same for the phase inverters if you still find the Joplin track harsh..
The original circuit was often derided and considered to be inferior to any newer modified driver boards.This as some have speculated was purposely promoted by the makers of those driver boards. Bench testing actually shows that the original design is quite excellent up to full rated power. Yes different driver boards will have different sound, but one would have to try many variations in order to see if they are actually preferable, and as you yourself discovered it can vary from song to song. I consider the OEM circuit as designed to be a real ST-70, the others are just similar to the ST-70. Great video by the way.
nice video and review on comparing the two amps. Have owned quite a few of the original ST70s over the years. Interesting comment on the difference in feedback between the two versions. This could be accounting for the sonic differences heard between the two amps. As a follow up might be interesting to measure open loop gain, then measure gain again with each amp's feedback employed to see how much feedback was used in each design. Was surprised to see those output transformers could go that low in freq.
