Dynaco MKIII Rebuild

I bought a set of Dynaco MKIII in working, but marginal condition. I decided to rebuild them for client.

The driver boards are being upgraded to 6SN7 based boards. And the units are being completely rewired with new tubes.

I will document the build in this thread


For reference, here is the Mark III manual
Dynaco Mark III Assembly Instructions.pdf (3.6 MB)

Here’s the way I found the amps …


Before starting the project, I needed to consider the objectives.

  1. Improve the look of the hand painted transformers
  2. Maintain some original patina
  3. Make sure the amps run stable for hours of high volume use

I decided to remove the transformers, transformer bells, and hand polish, but not restore the chassis.

I also decided to purchase new boards from one of my IG followers. I’ve tried replacing updating on previous Dynaco re-caps, and found them finicky and difficult to work with. I wanted this build to be stone reliable which was more important that pure orginality.

Here are the boards I decided to use:

Install instructions:
MK3 Octal v22.pdf (1.0 MB)

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Eager to see your progress on this! I am running the VTA 12AU7 board in my ST-70 rebuild for the last 2 years or so, and it really does sound nice. Plays well with every source I have tried with it too.

Interesting that the MK3 driver board appears to use half of the input stage 6SN7 unused… you could very easily configure that as a cascode stage for the cost of a handful of passive components.

The stock config on the VTA70 board is great, but I did recently switch from the supplied Audyn caps to Mundorf EVO paper-in-oils, jury is still out on those. The main improvement was that I made a very specific point to determine the outer foil leads and point those towards the lower impedance side of the circuit, which seemed to make a difference in noise I was getting in one of the channels.

These are a bit out of order, but here is one board wired in …

I find reviewing these pics like the one above pretty valuable. I did find one wiring error while reviewing the pic

Big iron mounted on unit 2

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