Dynaco MKIII Restoration
50 Watts per block
2x KT88s, 1x 6AN8s, and 1x 5U4G per monoblock
These were actually MKIIs that I converted to MKIII. The major difference between the two is that the MKII used a
C-R-C filter in the PS, A-430 OPTs (has no 4 ohms secondary tap) rated at 50W, and a pair of EL-34s. I purchased these
from a guy in San Francisco, who supposedly had them restored by a friend of his. What I saw was one of poorest restoration
job I've seen - sloppy solder job, wrong resistor and cap values, and so forth. One of the blocks wasn't even finished. At
least the chassis and iron bells were professionally powdercoated. But in teal blue? It took a while to get used to it, but
it turned out ok. I paid $300 for the pair and I was basically paying for the chasses and irons.
The first thing I did was to remove all passive components from the PCBs,
clean them up, then repopulate them with new ones. I was very tempted to get a pair of much talked about Posiedon boards from Shannon Parks, but I decided to restore using the original board. I mostly wanted to hear those British GE 6AN8s, which
are basically Mullards.
So, here is where the real fun began. I totally gutted the inside and rewired the whole thing. Like I mentioned earlier,
I wanted to convert this to MKIIIs. This involved adding a choke in the PS and using KT88s. I also put in a new filter can
cap, a fuse holder, a new bias pot, new ceramic sockets, new speaker terminals, a new power switch, and other many others
stuff that I can't remember. The original MK designs had some issues with the filter caps going bad, as the wall voltage
today has increase to 120VAC from 115VAC. This drove up the B+ past the maximun rating of the filter cap on the start up,
causing the failure. I circumvented this problem by using the 5U4G that has a little more voltage drop than the GZ34. BTW,
has all the stuff you'll ever need for Dynaco repairs.
So, how did it turn out? Pretty good over all! Very controlled bass and good resolution through all frequencies .
They didn't sound bad at all, even though I have to honestly say that I liked the sound of DIYTUBE ST-70 better. The ST-70
seems to be more musical and have more warmth to the sound. Also, the bass on these monoblocks wasn't as strong as I had
hoped. What I was looking for was something that will shatter windows around the house with that raw 50 wpc output. Instead,
what I got was something that sounded more like a big single ended amp. Maybe that's a good thing?