Dynaco Mark II to III conversion - tubes4hifi + SDS Labs

Hello.

I acquired a pair of Dynaco Mark IIs that I plan to mod to essentially convert them to Dynaco Mark IIIs.

I plan to replace the quad cap with SDS Lab's power supply board and I plan to use tube4hifi's Mark III driver board.

Has anyone here made this upgrade as well? Since the Mark II transformer doesn't come with a 16ohm tap, what do I do about the NFB connection?

Any other issues I should keep in mind?

Bob had posted this official bulletin from Dynaco on converting Mark IIs to IIIs, but not sure how relevant it is considering I'm going with a modern power and driver board: https://dynacotubeaudio.forumotion.com/t4126-dynaco-mark-ii-to-mark-iii-conversion

Cheers!

tacuba wrote:Hello.

I acquired a pair of Dynaco Mark IIs that I plan to mod to essentially convert them to Dynaco Mark IIIs.

I plan to replace the quad cap with SDS Lab's power supply board and I plan to use tube4hifi's Mark III driver board.

Has anyone here made this upgrade as well? Since the Mark II transformer doesn't come with a 16ohm tap, what do I do about the NFB connection?

Any other issues I should keep in mind?

Bob had posted this official bulletin from Dynaco on converting Mark IIs to IIIs, but not sure how relevant it is considering I'm going with a modern power and driver board: https://dynacotubeaudio.forumotion.com/t4126-dynaco-mark-ii-to-mark-iii-conversion

Cheers!

As for the output transformer; MkII HAS a 16 ohm tap. It is missing a 4 ohm tap compared with
MkIII.

What you intend is basically to create a pair of donkeys from a working Dynaco's :-(

Well, it _might_ be as good and it does use tubes in current production. But it is no Dynaco and that
will be shown at selling time ( or fault diagnosing)

Myself would have followed Bob's advise.

Thank you for correcting me about the 4ohm vs. 16ohm tap.

To clarify, one unit is a Mark III (A-431 with choke) and the other a Mark II (A-430, no choke). Both are in such disrepair that a complete overhaul is warranted.

I didn't grow up with these units and don't mind straying from the original builds.

That said, thank you for the reply.

tacuba wrote:Thank you for correcting me about the 4ohm vs. 16ohm tap.

To clarify, one unit is a Mark III (A-431 with choke) and the other a Mark II (A-430, no choke). Both are in such disrepair that a complete overhaul is warranted.

I didn't grow up with these units and don't mind straying from the original builds.

That said, thank you for the reply.

Departures from the original Dynaco has seldom improved the performance but always
made cost higher and introduced problems with later service. It will usually reduce the
value as folks that want a Dynaco would like an unmunged one.

That said you will get most benefit with staying original with compatible parts. But it's
your amp and you can do what you want with them.