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Dynaco S400/410?


Dylanl

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It's supposed to be one of the best giant power amps of its era (mid seventies). In fact, a reveiwer whose opinions I respect claimed at the time it was the best solid state amp available. It also has a power limiting switch which might be handy. Beware of poorly assembled kits and units which have been used in p a systems.

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The 400/410/416 was designed by James Bongiorno, he also designed models for GAS, Marantz, SAE.

An SAE 2400 sounds much better than the rest.

The Heathkit AA1800 is similar, but designed by prof MWLeach of Georgia Tech.

Will blow the others away (hard to find).

A GAS Son of Ampzilla with about $4 worth of bypass caps is a good choice too, 150W/4R.

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If you tack a 0.1µF film cap in parallel with C1 and C7 for each channel, and a 47µF 100V electrolytic across each of the two large 10,000µF main filters, the improvement in sound will startle you. Observe polarity on the 47µF caps.

About $4 worth of parts.

If you really like the amp and want to keep it for a long time, replace the 25 year old outputs and drivers before the amp blows up. Use MJ21193/94 and MJE15030/31 from Digi-Key.com (about $30 for both channels). If you wait 'till it blows it will cost over $200 for a tech to repair, and it could take your speakers with it.

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The author's advise is good, even though he doesn't know what he is talking about.

The resistors mentioned set the input bias to the slave connected drivers and are not connected to the emitters.

The ST-150 does not have these resistors, does not use the PC28, but the PC43.

As a bare minimum I would replace the plastic driver transistors too, they cost less than $1 each ($8 total cost). When these fail they take the whole amp with them.

Your choice.

For home use the ST-410 sounds better than the ST-400 or 416 because it does not have the extra HP/LP filter board or the Dynaguard. The 416 is better for low impedance loads and may be modified to the same input path as the 410.

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On 6/20/2005 3:55:18 PM Dylanl wrote:

Have any of you ever listen to or seen this SS amp? It is supposed to be 200 watts per channel. If you have what are your thoughts?

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I have owned a 410 for a number of years. Mine was either factory wired or done by a competent tech. Haven't tried it on my Klipsch speakers but it is able to drive electrostatics quite well. I haven't used it for a while due to a bad power switch (and the availbility of other amps) but I remember being a decent amp.

Dave H

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"DJK, have you seen this mod done before and where would I get the parts?"

More times than I can remember, I have two ST400 right now.

Get the catalog from Mouser and Digi-Key. Call your order in. Online stuff takes too much time and is not secure.

It would be easiest to use the original driver transistors, TIP41C and TIP42C (four of each).

Four 0.1µF polypropylene bypass caps.

Two 47µF 100V axial lead electrolytic caps for the power supply.

Four 1K 3W~5W and four 750 ohm 3W~5W (the more expensive 3W are generally better than the cheap 5W).

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I don't do photos yet.

I buy blown Dynaco for the sheetmetal and transformers, junk the boards, and replace with WMLeach designs.

The 400/416 is laid out very different than the 410, other than the PC28 and the transformer there is little that is similar.

Do the cap mods first, it will totally change the sound of the amp for little or nothing.

If you decide to keep it then do the resistors and drivers.

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On 6/23/2005 4:54:51 PM Dylanl wrote:

So far 1st listen I am not very impressed.

I also PM you.

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Forgot to mention - there were tantalum input caps on mine which I replace with jumpers. My tube pre has output caps so they weren't needed. Probably helped but I made the change before serious listening so I can't say with any conviction.

Dave H

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  • 5 years later...
  • 10 months later...

Hi everybody,

So is Dynaco ST410 worth getting? I came across one for ~120$ and think of getting it as my main amp for Klipsch KG 3.5 (just bought them as well and have not even unpacked yet)..

Or should I look for something like 70s Marantz or 80s-90s Arcam?

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Just a short note here ... For those that do acquire a piece of Dynaco solid state or tube gear and would like to work on them, tubes4hifi.com has nearly all the original Dynaco assembly manuals online FREE for the downloading. See links below.

Dynaco solid state manuals > http://www.tubes4hifi.com/dynaSS.htm

Dynaco tube manuals > http://www.tubes4hifi.com/downloads.htm

Bob Latino

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