The Dynaco Dynakit ST70 Stereo Amplifier Restoration Project Part 1
ฝัง
- เผยแพร่เมื่อ 14 เม.ย. 2019
- This is the beginning of what is the second phase of a greater project going back several years, that being the initial salvaging of this amplifier after being found stored in a Florida attic for over 40 years. For this effort a complete video series exists where the amplifier was brought to a working order but left in the original patina also retaining the use of less that reliable parts, which have caused unpredictable issues over the years.
As a primary platform for this restoration, I've opted for the stainless steel chassis from dynakitparts.com along with new pots, switches connectors, screws and so-forth. Further work will be the cosmetic restoration of the transformers as well. An unboxing goes into each part and kit specifically. A smaller secondary unboxing comes later in this episode.
The project itself begins with the removal of the output transformers which i've opted to recolour on the ends of the cables on both sides due to fading. At that point it was safe to cut out of circuit. This process includes cable to the rectifier and the power transformer as well as the selenium rectifier, some of which have two colours. Once all cables are clipped, starting with the power transformer, each are removed one by one. Emphasis for the power transformer starts with the connections on the c-clamps. Output transformers are removed in a similar fashion, noting that the red center tap wire goes all the way to the electrolytic capacitor and needs to be pulled back on one side.
With all transformers removed the covers are unscrewed and separated so that they can be sandblasted and painted. All of the inner transformers appear ok. I take the covers to Jason's bug ranch and put the covers into the sand blaster to clean then which also textures the raw metal for good adhesion. The first painting attempt as a high gloss, didn't go well. too many imperfections in the metal, and dust and wind in the shop. A second attempt after a stripping and re-degreasing came out perfect by allowing for a light texture to come through, almost like a leather or knockdown.
Each of the transformers are masked and sanded with a Dremel for rust removal and painted as well, cleaned at intervals with spirits. During this time, custom threaded rod with acorn nuts are made for the restored transformers to replace the old screws. With all of these pieces, the reassembly of the transformers commences. Paying attention to stamp placement, the output transformers are done first, doing the measurements of the studs for the final cut. With that the covers are tightened down.
The power transformer is assembled last, also ensuring that the cover is on in the correct direction. The rod length must account for the new dampeners so no adjustments will be made at this time. Having completed the transformers, this concludes the first video in this project series. #dynaco #st70 #tubeamplifier #antique #restoration - วิทยาศาสตร์และเทคโนโลยี
Love this!! You are a legend keep up the good work! We future generations are fascinated by your skills and I for one am deeply focused on learning all of your knowledge as well as other masters like Uncle Doug. Greetings from Ventura, California.
Very nice work, Jordan. The new chassis is really beautiful and I like your detailed renovation of the transformers. We're looking forward to Part 2 :)
Thanx Doug!
Uncle Doug always a fine thing to see you involved in Dynaco amps. My dream is that you would do a video of restoring my beloved PAS-3 Dynaco tube preamp.
I don't work on them, Jules, but I can't help but admire the fine work done by Jordan. @@julesl6910
Very obviously a "labor of love"
so nice, good teaching video. Thanks, I am looking for part 3.
Glad you enjoyed it, Part 3 should be released within a month
Fantastic Work man!
Thank you.
a thin bicycle wrench may be helpful to keep the nuts under the transformers from turning
Just a quick heads up to anyone else going down this road. I had no need to sand blast; I was wiping down the end bells with acetone when I noticed that the paint was coming off! Yay! More acetone and some bristle brushes and rags and the job was done. Try it.
I wasnt removing paint... rust, and a surface for new paint created.
A trick I learnt when cutting threaded rod or bolts with acorn nuts is to install the threaded rod with a standard half nut (depending on the depth of thread in the acorn nut) and then marking the threaded bar before cutting it.
Thanks for sharing
Nice!!
Thanks.
Nice! Would it not be better if you dipped the trafo core in lacquer to laminate them so they won’t hum?
These transformers are perfect, I wouldnt mess with them.
Great work….please do restoration video for eico hf-81
You give me an amplifier for a gift, Great!
Using a wire wheel to remove rust off the transformer plates? If you remove the insulation coating?
Is there a question in there. Or two statements.
Wonderful amp, love mine. It tended to blow fuses though so I replaced the rectifier with a solid state Weber Copper Cap. Works great as you can see in this video: th-cam.com/video/cLIOW28RxXo/w-d-xo.html
Tell Jason that the generator on the VW engine needs to be rotated 90* clockwise.
That has what exactly to do with an amplifier?
Any idea how many man hours went into your transformers work?
Not counting install or removal from the amp. About 5 hours altogether.
You should of built up a few layers of primer to fill the defects then painted them glossy
Rust-Oleum red rusty metal primer fills the best
I could have also used metal filler as well, they werent that bad though.
how does an EL34 differ from a 6V6?
Well, they are power tubes, and thats were the similarities end...
I have an original and looks better than the one in the video. I don't want to change anything I want all original parts, I don't want to change the sound to fit today's music. Mine will be playing classical and big band music like I heard in the late sixties on FM. There is only one part that must be upgraded to solid state and it's the selenium rectifier because the original will not be any good and there is not a replacement available. But all other parts including tubes, Capacitors, resistors, rectifier tube all can be replaced with new old stock. The capacitors will have to.be new of course just exact values will be used. I have both the preamplifier and st-70. I want to start with the st-70 the preamp will need some upgrading because a CD player will be added and need impedance matching. And require more research. But the ST - 70 will be original . 73
My selenium rectifier still works, nothing wrong with it. Only bad caps blow out these rectifiers, the rest is internet myth. Remember that there were several cost cutting measures in the original design, one being the power supply caps so keep that in mind.
@@retrotechandelectronics as long as it sounds the same. I don't like some of the new designs and I will never use diodes instead of the rectifier tube. Those are the two main things. I had a friend's dad replace a 10 uf and used a 40 uf on an antique radio which was ok the only thing I didn't like is that nasty shock because the 10 uf was drained out when the power was disconnected but the 40 held a charge. I guess the coil discharged the 10 quicker than the forty. I was in Jr high and didn't know better when I messed with tubes and didn't discharge the 40 uf cap. But that's not my only reason for using equal value parts I also like things original if I had two identical amps I would listen to both and then make my final decision. I knew people who had original st-70 and st-35 and both sounded great with no modifications. If I decide to change the values and like them better I will post my findings. I haven't checked anything on the amp so I will check that selenium rectifier and if it's still good I will leave well enough alone. Thanks for telling me your valuable information. I did buy a diode but I don't have to use it. I bought new tubes because the old ones were broken the rectifier and one El 34. I'm kinda glad I didn't try to power the amp up. Maybe the selenium rectifier is still good. Thanks again. 73