Dynakit Stereo 70 Project 

Nice video! Not only did I geek out about the amp, but also the HP48 in the background!

I like your high end multi meters! I have my father’s ST70, PAS and tuner which he built in ‘66. I went through it about ten years ago with new ecaps and replaced the selenium rectifier in the preamp and a few other recommended components. Just recently brought it back from a hum issue and it’s running like a top again. Nice job on your amp and the video.

There’s one in my Grandfather’s attic. If I can have it good to know I can have it rebuilt too! Great video thanks for sharing.

Very nice work. I’ve been putting together a Dynakit system I’ll be working on soon, myself. An ST70 kit from the early 90s to build, an FM3 kit from the 60s to build and a PAS that needs a full tune-up. Also got a set of A25s that need a little work. Was surprised to find the Jensen bi-directional electrolytics in the crossovers measured fine with zero leakage, but I’ll probably still replace them with films. Maybe some new cloth. Quite a project, but hopefully in a month or two I’ll have a nice little vintage system. Glad to see you’re getting good enjoyment out your nicely resurrected amp.

Hi, I've built many of the Dynaco St70's with VTA boards. When Roy Motram made the VTA board, he based on the VTL circuit. What I finally did was was change the values and adjusted the FB loop for 12AU7s or 12BH7s because there is way too much gain with the 12AT7. You can use a 12BH7 but you can also wire it for a 6CG7 because you have more than enough current with that nice power transformer you have. 12AU7s are much more linear when you run them at 8ma. Another thing I do is run a 35uf film cap off the rectifier in place of the 20uf lytic. This gives it much more kick in the base region I also put in higher wattage carbon films in place of the half watt metal films because you will notice that the plate load resistors get pretty hot. This is still the best Dynaco ST70 replacement board I have ever used.

Another interesting video. Never had any tube amps. I remember tube tvs from when I was a kid, though.

Excellent vid! Thanks for the warning about not having the cage on 👍

Sisters of Mercy! Reminds me of my youth.

Beautiful work under the hood! Loves me some winged C’s! Wish I’d bought more too. Cool vid, man!

For decades there has been a debate over the efficacy of the PC-3 board. It may have been frame as "notoriously terrible", but I don't agree. But, there is a reason for supplanting it with one of the many boards that have been made available to replace it - the 7199 tube. They are almost unobtainable at this time, with no prospect of them ever being manufactured again.

Sounds good :)

You did a beautiful job on the amp. However the 12at7 is not more linear than it's counter parts. The 12au7 is the most linear and is actually a 9pin version of the famous 6sn7. Also the original tubes sound just as good if not better. I have tested them on every piece of equipment you can imagine. I'm not trying to insult you or you work just want people to get a accurate account of the amp. Also there are 2 available tubes that need a repin but are very close to the 7199. The 6u8 and even better is the 6gw8 I believe.

Excellent video, my son-in-law just bought one and is looking for a preamp to mate with it and his KG4 speakers. He listens to records, any experience with sub $1,000 preamps?

I have one that I will have to rebuild when I get the time

Hello sir I would like to chat with you about my vantage dynakit ST70 amp do you service or repair systems for clients.

im thinking of buying the driver board from "Tubes4 Hifi". i want to get the one with 3 "6sn7" tubes. do they have some kind of instruction on how to adjust all the settings on those boards?

I just picked up a Dyna FM Tuner, Dyna Stereo Preamplifier and a DynaKit stereo 70. It has sat for years. I have not plugged it in and do not know anything about it. What should i do before i plug it in, any manuals online for this? Any help\info please :)

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: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-cLIOW28RxXo.html

ST-70 is good, but I do not like the electronic parts outside, I am going to rebuild one of my st-70 and hide these electronic parts inside and only leave the two 7199 tubes outside.

Pretty weak power.