Dynaco ST70 KIT - your opinion please

[Eli Duttman]

A single thermistor goes in the line between the diodes and the PSU filter. With a 5R4, I suggest a CL90. There's no reason to believe that selection will fare poorly in combination with SS diodes. If the part doesn't heat up enough to bring the cold resistance down a lot, you can try wrapping it in wool or acrylic yarn and encapsulating with heat shrink.

The data sheet for the NTC inrush current limiting thermistors is here.

[SandyG]

Michael

You have a ton of good stuff if you look around. I jump started with some Dynaco projects and all have had great results.

If you are looking for more of the original Dynaco start with this -

Welcome to DYNAKITPARTS.com

They have a good variety of dynaco kits and are pretty true to form. I bought a couple of trashed Dynaco MKIII and basically chucked out everything except the transformers, power cords and metal covers. All the rest was essentially the MKIII kit from them. I upgraded the driver which I got from Triode electronics.

The second path is Triodes kits, never built one but looks pretty good.

The last one is the Tubes4HiFi (Bob Latino). He has a few different amps, but the one that I really like is the ST70 well the ST120 version of it. The kit is well packaged with everything down to the wire for assembly and has a very good set of build instructions. It's my second favorite amp that I have and it's very powerful all in a compact Dynaco ST70 box. Has a ton of options too.

tubes4hifi home page

The last one to check out is the OddWatt series, I have not built one but they look like a nice package, don't have the link but you should be able to find one.

As a side not I had only thought I would build the ST120 and be done. 6 Monoblocks later... You get the idea, yes another pair in the works, a quad KT88/KT120 just to round out the collection .

Enjoy the addiction!

Sandy

[prairieboy]

Originally Posted by rongon

Hi Eli -- I'm interested in adding those thermistors to my mutant amp in an ST70 chassis. I'm using SS diode rectification, getting about +460V. What specs to look for in the NTC thermistors? What resistance spec? Small in value, like 100R or less? Or more like 1k? Thanks for the idea.

Oh, and where do they go in the circuit for slow ramp up of B+? Perhaps in the center tap of the power transformer?

I have an ST-70, using the Classicvalve octal board, with their psu board and SS diodes. I have a C90 in the AC line before the transformer, which seems to be the common place to put it. It works well, but allow clearance because it does get quite hot.

[zimmer64]

Gents,

Thank you for your great input and feedback. I must admit that I am out of my depth as to all the detailed technical advise, which you provided.

I guess I will start off with one of the standard kits from either Tubes4hifi or the Triodes one. Once the stock kit has been built I will proceed applying the suggested improvements.

I will post my progress here in the forum.

Thanks a lot folks.

Greetings from Switzerland

Michael

[zimmer64]

Just to let you guys know. I have ordered the ST70 kit from Tubes4hifi last night.

Thank you for helping me decide.

Michael

[SandyG]

Its a reall good kit, just follow the directions and take your time and it will go together very easy.

Enjoy!

Sandy

[Tony]

I bought an "EF86" from triode for my organ, it was actually a Russian 6 pi something tube.

it's a 6J32, russian equivalent of the the EF86....

[Zibi]

http://www.klausmobile.narod.ru/td/list_e.htm

[zimmer64]

Just to briefly report back: the kit arrived yesterday safely here in Switzerland. Sales process, payment and shipment went flawlessly. Bob Latino of tubes4hifi is very helpful and responsive. I shall post pictures, once I completed the kit.

Thanks again

Michael

Michael's Project Page

[zimmer64]

The kit is extremely nice. Every part is individually packed ina zipper bag and clearly labeled. The manual is good as well.

Michael

Michael's Project Page