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dynaco_dan

Dynaco amp mods and tweeks

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I have a few mods or tweeks information on Dynaco's ST-150, ST-400, ST-410, ST-416 amps also series 80 amps and ST-120.

If there is sufficient interest I will follow up here in the near future.

If I remember correctly there was a phase 2 Dynaco ST-400, I have no information on why there was this added model designation. It may have been an internal doc.

Please post here if you are interested in following up on these issues.

Remember there is a serious risk of shock if you are not experienced.

There was a TIP mod well known for the ST-120 but there was also a similar TIP mod for the 80 series. 

The mod for the ST150 - ST-416 amps is on Greg Dunn's web site. It was posted there around 2002. You can print out the article.

A set of 8 pages has been deleted there that would have created a 600 watt mono amplifier. No explanation posted. Perhaps liability issue.

 

Vern

I do not have an email address yet.

 

 

 

Edited by dynaco_dan
Added more info

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I have a couple of Dynaco 416 amps that I drive my AR9's with.  I recapped them myself and they sound wonderful.  I'm not likely to try and mod them, but I am always interested in any information I can find on them.

-Joel

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Hi Joel

The site referral is a site without an active forum.

The repair was written by Kevin Boales for PC-28 circuit boards.

I can print out the St-400, etc, mod for my use but I do not know how to just save it.

This mod is for usually one dead channel and it covers replacing a common cause of the one dead channel.

I do not feel it is ok for me to print out that file and re-scan it and post it here.

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I'm pretty sure I've been to Kevin's site.  When I recapped the ST416, I upgraded a couple of resistors.   Is that the mod you are referring to?

-Joel

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Hi Joel

Yes the original composition resistors were slightly under-rated and that chap, Kevin, takes us through the steps to get to and replace them.

After completing those replacements we get a helping hand to reset the bias.

Only listed tools, parts and a VOM are needed.

Which caps did you replace and were the new ones 85' or 105'?

Did you strip the amp right down to it's basic components?

Great job for someone here to do, you must be highly skilled.

I picked up a Dyna 400 with meters here because one channel was dead.

It is really ugly as it was tinkered with and likely stored in a damp carport.

Less than $50.00 though, another of my rescues.

I went to the directory here and see over 80 viewers have seen some or all of this topic.

I wish some of those viewers would leave a comment or?

Nice to see this amount of interest in this topic.

Edited by dynaco_dan
additional comment

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On ‎06‎/‎04‎/‎2018 at 8:23 PM, dynaco_dan said:

Hi Joel

Yes the original composition resistors were slightly under-rated and that chap, Kevin, takes us through the steps to get to and replace them.

After completing those replacements we get a helping hand to reset the bias.

To add to this heading I was reading about a Pat-4 preamp that was noisy in only one channel.

The writer replaced only one composition resistor that must be 40 years old.

Noise disappeared.

There is a need for replacing those old composition resistors with metal film or ?

 

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1 minute ago, dynaco_dan said:

To add to the Dynaco ST-400 amp story.

I have a vague memory of the resistors across the top of the relay plate that was also a choke-coil assembly.

My memory cannot be relied on but I believe the coil wire was originally a red colour and a mod was instructed by Dynaco at that time.

I quote from Audio Magazine May 1975 page 49, a review of the Dyna 400.

This is a direct quote from Dynaco.

"Dynaco informs us that a very recent change in the value of the resistor R305  to 1.8 ohms reducing the Q of the output inductor-resistor combination effects an improvement in high-end sound quality.

This is easily made on existing St-400's by adding a 2.2 ohm resistor (2 watt minimum) in parallel with each output inductor (choke-coil assembly) on top of the relay mounting plate.

This will also noticeably improve the square wave trace into a capacitive load, especially at low drive levels."

This review was 3 years after it's introduction.

If my memory  serves me correctly the colour of later kit coil wires was changed to black.

If you should have black no mods are needed.

The St-410 and 416 would also have black as they were designed later on.

Vern

 

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On ‎28‎/‎04‎/‎2018 at 12:21 AM, dynaco_dan said:

 

Hi again

Here I am with some more trivia about the Dynaco 400, 410 and 416 amps.

Today I found an article which I will write about another day and perhaps scan and post here.

It is a more detailed story about the coil/resistor which I discussed earlier.

The colours were correct but they used a black plastic sleeve over the coil.

I also came across a copy of the MBI-400 super-charge mod which can increase the mono output to 600 watts

This is one of several links that has disappeared from, home.indy.net/~gregdunn/dynaco/components.

That site does not have a forum, sadly, because Gregg has done a beautiful job setting it up.

Also I came across price lists both retail and wholesale which I need to scan first.

To change the subject here, I see lot's of viewers but only a few get involved with this site.

If everyone visiting could post an answer or a question it would be great, even if no one here can answer it.

Especially me.

Also if everyone could post a photo of an article or ad they have of old Dynaco.

Vern

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