I have a pair of these amps...The manual say's:
The Dynakit Mark III-70 is identical to the Mark III with the addition of a 70 volt
output for line distribution systems. A different transformer (A-431-70) and a five
screw terminal output strip are the only variations.There is an additional white wire
coming out of the output transformer. This should be connected to the fifth terminal.
Obviously, this transformer is mounted on the more common Mark III chassis having only
the four screw terminal. You can just terminate this lead. (tape off)
Manual further states: The use of the (4)(
and (16) ohm outputs is unaffected by the
presence of the 70 volt output. The output impedance of the 70 volt tap is 83 ohms.
When the 70 volt output is used, there are commercially available loudspeaker matching
transformers designed specfic for this application delivering up to 60 watts continous
I should note that original chassis for this model had a wider cutout to mount the
five screw terminal strip. The fifth screw position was screened as 70V.
Kevin @ Dynakit