by EWBrown » Fri Mar 06, 2009 7:22 am
If you are building this amp on an ST-70 chassis, then the Triode A470s are the best choice, as they are virtual "clones" of the original Dynacos, and will fit the chassis perfectly. The other OPTs are most likely somewhat larger and heavier, and won't fit onto the ST70 chassis.
The original A470s were 4300 ohms, CT, and that impedance is a good target, 3400 ohms may be a bit too low, though they may deliver a bit more power.
Using the 60 watt OPTs would be overkill, in this application, as the ST70 was 35 watts per channel.
The Triode PA060 has more current handling capability and will not run as hot as the vintage Dyna power trannies.
The ST70 driver board from DIYtube and the VTA-70 driver board are both excellent circuits, and the boards will fit onto th ST70 chassis perfectly. I'd also go with one of the SDS or C Chong cap boards, instead of the multi-section "can" cap.
The cap boards fit under the optput transformer, inside the chassis. Some of these also have the bias circuitry on them, and the VTA-70 driver board has the bias circuitry and four independent bias adjustment pots on board.
HTH
/ed B
Last edited by
EWBrown on Fri Mar 06, 2009 7:27 am, edited 1 time in total.
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