Let's Restore A Dynaco ST-400!

[Jim Marantz]

Jim you're the best! Thanks for your help and for taking the time to reply in such detail.

Chris, see the picture below of my meter LED. I removed both neon lamps (which were dead anyway) and replaced them with one LED lamp that Ed at Qau-Co made for me. I'm sure he'll make them for you too if you ask him. It's actually (3) LEDs in one fuse type package. The meter lamps run on 15V tap off the PC30 power supply board. (-) is 18 on PC30, (+) is 13 on PC30. PC30 resistor R318 maintains the 15V. If you wanted to use another voltage rated LED you could play with the resistance value there.
The LEDs I installed are blue in color. I actually plan on switching to white LEDs as the meter needle gets washed out on the blue background with the blue LED.
Good Luck.
Jim

 

[Chris Dykes]

Chris, see the picture below of my meter LED. I removed both neon lamps (which were dead anyway) and replaced them with one LED lamp that Ed at Qau-Co made for me. I'm sure he'll make them for you too if you ask him. It's actually (3) LEDs in one fuse type package. The meter lamps run on 15V tap off the PC30 power supply board. (-) is 18 on PC30, (+) is 13 on PC30. PC30 resistor R318 maintains the 15V. If you wanted to use another voltage rated LED you could play with the resistance value there.
The LEDs I installed are blue in color. I actually plan on switching to white LEDs as the meter needle gets washed out on the blue background with the blue LED.
Good Luck.
Jim
View attachment 850392

Thanks so much Jim! I had already ordered a set from Update My Dynaco - so I'm working with a slightly different set up but should install similarly! My meter background is white and the meter case has a blue acetate film inside. I'll get the leds set up and see how it looks! Thanks again for being so helpful!

 

[Chris Dykes]

Teardown still continues, but I have managed to get some of the amp back together.


Dude, where's my amp?!!?
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I took the opportunity to strip the old paint off of the chassis and "Z" bracket.
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The power supply board PC-30 is completely rebuilt.
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I rewired the power switch, circuit breaker, tranformer and thermal sensor system. Painted the chassis components with textured paint. Cleaned up and tested the transformer, rewired / rebuilt the fuse plate and speaker relay with all new components, and installed the main power caps.
View attachment 798660

View attachment 798661

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I'm currently replacing all components on the output boards and scrubbing everything clean to start on the output/heatsink section of the amp.
I hope you like it. It's been a lot of work thus far.

Hi Jim - I'd like to replace the .1uf capacitors on the relay plate. Can you tell me which brand you used to replace yours?

 

[Jim Marantz]

Hi Jim - I'd like to replace the .1uf capacitors on the relay plate. Can you tell me which brand you used to replace yours?

I like these. You can never go wrong with Vishay.
http://www.mouser.com/ProductDetail/Vishay/S104Z93Z5VL83L0R/?qs=MZE/3ll%2bp/ba6C%2bzoK7Jpg==

 

[Respighi]

I like these. You can never go wrong with Vishay.
http://www.mouser.com/ProductDetail/Vishay/S104Z93Z5VL83L0R/?qs=MZE/3ll%2bp/ba6C%2bzoK7Jpg==

Jim

This thread is an inspiration. I picked up a used, untested Stereo 400. It worked for an hour or so before smoke came out and it died. I've ordered replacement driver boards w/parts, caps for pc29, and main filter caps from Qua-Co. I'm looking forward to getting into this project and I expect I may have some questions for you down the road. Thanks again for your great pictures and explanations.

John

 

[Jim Marantz]

Jim

This thread is an inspiration. I picked up a used, untested Stereo 400. It worked for an hour or so before smoke came out and it died. I've ordered replacement driver boards w/parts, caps for pc29, and main filter caps from Qua-Co. I'm looking forward to getting into this project and I expect I may have some questions for you down the road. Thanks again for your great pictures and explanations.

Don't forget pc30, the power supply board. It's probably shot like mine was. qua co has a rebuild for it.
Jim

John

 

[Respighi]

I finished my Stereo 400 project. New driver boards with all new components, recapped PC29, new output transistors, new relay, new main filter caps, new old stock Dynaguard switch. I built 2 Stereo 400s 40 years ago. I can't remember if they sounded this good, but this is amp exceeded my expectations. Effortless, totally free of listening fatigue, seemingly unlimited headroom, bass that kicks like a mule. Very satisfying project.

 

[Northwinds]

I had a 400M, I liked it while I had it

 

[Chris Dykes]

I finished my Stereo 400 project. New driver boards with all new components, recapped PC29, new output transistors, new relay, new main filter caps, new old stock Dynaguard switch. I built 2 Stereo 400s 40 years ago. I can't remember if they sounded this good, but this is amp exceeded my expectations. Effortless, totally free of listening fatigue, seemingly unlimited headroom, bass that kicks like a mule. Very satisfying project.

Need pics! What system is a part of? Which speakers are you driving? So happy for you!

 

[Giordano]

Hi, I'm Giordano from Italy,
I have bought on Ebay.de a Dynaco Stereo 400 220 VOLT 50 Hz amplifier that needs a restoration.
Can anybody give me the e-mail address of Ed of Qua-co? I have to send him a request for the material I need.
Many Thanks
Giordano.

 

[Chris Dykes]

Hi, I'm Giordano from Italy,
I have bought on Ebay.de a Dynaco Stereo 400 220 VOLT 50 Hz amplifier that needs a restoration.
Can anybody give me the e-mail address of Ed of Qua-co? I have to send him a request for the material I need.
Many Thanks
Giordano.
View attachment 985592

I will send asap

 

[Giordano]

Thanks Chris.

 

[Chris Dykes]

Here's Ed's direct email: ed122@yahoo.com

 

[Jim Marantz]

I finished my Stereo 400 project. New driver boards with all new components, recapped PC29, new output transistors, new relay, new main filter caps, new old stock Dynaguard switch. I built 2 Stereo 400s 40 years ago. I can't remember if they sounded this good, but this is amp exceeded my expectations. Effortless, totally free of listening fatigue, seemingly unlimited headroom, bass that kicks like a mule. Very satisfying project.

John,
Bypass that PC29 board and you'll be amazed at the difference in sound. The features on that board are a relic. You can easily hook it back up if you ever wanted to sell it as "original". I'm glad you project turned out well.
Cheers,
Jim

 

[Giordano]

Hi guys,

Here is my work in progress:


PC-28, PC-29 and PC-30.
I ordered spare parts from Ed. The PC-28 will be put new. PC-29 and PC-30 will be rebuilt.


Does anyone know anything about this PC-31? Photo taken from the web.


And what about these caps? These GE 10000uF 75V do not seem to throw ...






Thanks,

Giordano.

 

[Giordano]

PS. I'll bypass the PC-29 by installing a selector just like in Stereo 416. I will follow the wiring diagram from the 416 manual.

 

[Giordano]

Today I riceived the original manual, from Germany:

and 1 brochure extra. Mint conditions.

Thanks Rolf.
Thanks ebay...

 

[KentTeffeteller]

The pinnacle of Dynaco Solid State amplifiers, a beastie to build in kit form. And a superb classic amplifier, though quirky with age like all good vintage gear can often get. A nice restoration, I love how nicely you did your work.

 

[GregDunn]

Since this appears to be an ongoing thread discussing ST400 updates - and I'm currently going through my 400s to make sure they're in good working order - maybe someone can share their experiences with me.

Every once in a while I look for degradation such as overheated resistors, failing caps, etc. and replace them; my amps don't get played as often as the used to, so I'm always on the lookout. Naturally, when I replace anything I check bias and offset to make sure something didn't get nudged or maybe damaged due to heat or age. My ST400 and ST410 are going through this right now, and when I put the 410 on the bench I was shocked to see that the bias in both channels was way high - over 300mA. Other than the greater heat, there seemed to be no other issues and after resetting bias and offset (offset really didn't need tweaking) it's been stable during "burn-in". A little nervously, I put the ST400 on the bench as well, and sure enough its bias was high, though not quite as badly (well over 200mA). Offset was within spec here too. FYI, I used 2 very different ammeters to measure with, and they were pretty close.

Has anyone seen this happen in a 400 which has sat idle for an extended period of time? The fact that both channels were nearly the same on each amp, and that the bias pots weren't far away from the center, puzzles me. I can't imagine something aging that would cause the channels to go over bias symmetrically, and on two completely different units.

 

[llwhtt]

How are you measuring the current?

Craig