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New (to me) Dynaco gear

Posted on November 26, 2015 at 17:36:26

Posts: 1
Location: GTA
Joined: November 26, 2015

Hi all,

New member and thought I would introduce myself, as I will likely be looking for some help and advice in the next few months.

I was given a Dynaco PAT-4 pre-amp over the summer and just got around to checking it out. One channel (left) is out, and all the pots are scratchy. Also missing the selector knob so need to source that. Otherwise it looks in good shape on the exterior, and knowing the original owner it was well looked after when in use.

To accompany it I picked up a Dynaco ST-120 amp on eBay for next to nothing, but cosmetically it is rough. Apparently it works, but I won't power it up until I have had a chance to look it over internally. I do know that the heat sinks are not standard, and who knows what other well intentioned mods were done. Pic attached.

Anyway, these will be my winter projects. Not looking to spend a lot of bucks on them, trying every tweak to improve the sound. My goal is to get them working and sounding nice, in close to stock configuration.

My main source will be an 1969 AR XA turntable that was given to me, and also I need of work, mostly cosmetic.

Georgetown ON


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RE: New (to me) Dynaco gear, posted on November 26, 2015 at 19:15:08

Posts: 460
Joined: December 29, 2012
I don't know if Joe typically does any work on these, but of course you could ask him.

Options for information, parts and possible services include eBay seller "qua-co" who I believe might be a former Dynaco tech: QUA-CO

There is also: UpdateMyDynaco

But, I'd think the first thing to do would be to get a hold of complete copies of the original assembly manuals and pictorial diagrams and sort out whatever changes have been made to them.


RE: New (to me) Dynaco gear, posted on December 6, 2015 at 04:16:09

Posts: 99
Joined: December 29, 2000
For info on the original (including schematics), look at the link below. There may in fact be improvements in the unit you have that you'll want to keep - you'll need to figure out whether changes were made, and if so, whether they're improvements (or not).

Typically at this age, the capacitors in the ST120 are dried out and need to be replaced. So at a minimum, plan on disassembling the amp, cleaning up the chassis, replacing all electrolytics, and reassembling. If there are actual circuit mods (and not just better heatsinks added to the existing design), you may want to think about whether you want to restore the circuit to the original.

What speakers will you be using? The ST-120 had trouble with low impedances and complex loads. Something simple like a Dyna A25 is a great match; electrostatics or low impedance monsters like AR-LST's not so much.


Schematics missing, posted on December 6, 2015 at 05:33:28

Posts: 99
Joined: December 29, 2000
Hmm, the schematics appear to be missing in that link I posted. I'm assuming a google search will come up with other sources. Sorry...


RE: Schematics missing - found 'em, posted on December 6, 2015 at 08:17:42

Posts: 99
Joined: December 29, 2000
Try here:


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