[mjcmt]

I'm looking into buying the Dynaco ST-80 power amp for my computer system as follows: iMac headphone output (use internal volume and eq) > Dynaco ST-80 > JBL  Control One (have 'em) monitors. Why the crummy sounding Stereo 80 you may ask? Because it brings back my childhood memories of my Sca-80 and my good friends Pat-4/St-120, plus I think it looks very cool and industrial, and has a small footprint. I want to rebuild it to make it totally safe for all day powering on with only night time powering off.

After I find one, what rebuilds would make it very safe. I'm handy at soldering, rebuilding, and meticulously cleaning if I'm told what to do. What do you think?

[avahifi]

This is not an easy one to upgrade.  Give me a call at 651-330-9871 if you would like some advice from someone who has built a few hundred of these years ago.

Regards,

Frank Van Alstine

[Wayner]

I have a nice Stereo 120 built into an AVA Insight 170. All new guts, including transformer. Only thing left original is the case. 85 watts RMS per channel and is one of the most musical amps that I own, in use almost every day.

Don't have a Stereo 120 chassis? Frank can put this amp into the small DAC chassis.

Wayner 

[smbrown]

Or, get a T-amp and hide it behind a PAT-4!

[mjcmt]

I don't think I'm looking for an extensive Dynaco upgrade, but more a replacement of potentially bad areas in the design to make it safe for extended periods. Improving sound quality to hi-fi status is not the important criteria for this situation.

Also I'm not looking for a preamp or t-amp. I'm partial to the vintage Dynaco power amps w/ the iMac controlling the volume.

[avahifi]

As I mentioned above, give me a call and I can probably help you with keeping that old ST-80 amp running as is.

Frank Van Alstine

[Wayner]

I don't think I'm looking for an extensive Dynaco upgrade, but more a replacement of potentially bad areas in the design to make it safe for extended periods. Improving sound quality to hi-fi status is not the important criteria for this situation.

Also I'm not looking for a preamp or t-amp. I'm partial to the vintage Dynaco power amps w/ the iMac controlling the volume.

The design was perhaps "unstable" as one failure would cascade thru the circuits, wiping out most of the transistors. That is what happened to my Dynaco Stereo 120. The only "safe" upgrade, is a complete upgrade.

Wayner

[avahifi]

Late in the production life of the ST-80 and ST-120 (both had essentially the same audio circuits), Dyna came out with a stabilization and durability upgrade called the "TIP Kit".  The name TIP referred to the new use of Texas Instrument Plastic TO-220 case transistors to replace the driver transistors on the audio boards, along with changes in capacitive compensation to improve stability. Previous generations of these amps were on the hairy edge of going into full oscillation and self-destruction.

Although I no longer have detailed info on the TIP Kit, I do remember that it came with good step by step installation instructions.  Perhaps if you Google Dyna TIP Kit or similar, you may find a copy of these instructions still available.  If the ST-80 is still working now, this would be a very good starting point, along with replacing all of the large chassis mounted electrolytic capacitors, which are now long past their useful service life.

Again, you may call me for more help.  651-330-9871

Wayne is right that the best result is with a full rebuild, but that is pretty expensive and it seems that is not what you are looking for.

Regards,

Frank Van Alstine

[dB Cooper]

Google search rocks:

http://www.davidreaton.com/Dynaco_120.htm

These apply to the ST-120 though. That would likely be easier to find than an 80; I believe the 120 was a lot more popular.

[avahifi]

There you go, this is exactly the information you need to get the best out of your ST-80 while retaining the stock circuits.

Everything shown in the link above is correct, except for the regulated power supply information.  The ST-80 has a simple RC power supply without the complex and unreliable regulated power supply used in the ST-120.

Have fun with the project.