Dynaco Upgrades Blackburn Audio ST-70 Upgrades
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This is an all octal based board with cascoded 6SN7GT's directly coupled to a 6SN7GT Split-Load phase inverter. The sound is phenomenal, more punch than you have ever heard in a Dynaco.
Features:
- High quality 0.062 Blue FR4 PCB with 2oz copper -Dale mil-spec resistors (RN-65 series)
- Solen metallized polypropylene coupling capacitor
- Extra pads to mount large coupling capacitors
- Can easily install 2W to 5W resistors for the PI making use of the 6BX7 or 6BL7 possible (Not without a separate filament transformer though, 1.5A ouch!)
- Huge octal sound
Okay so whats the catch? Well your right all this does sound a little to good to be true, the driver board will not work in a Dynaco ST-70 amplifier that still has the original power transformer. If this is an issue for you then please see our 12AU7 Cascode boards below which will drop into any Dynaco ST-70 without a problem. 6SN7's draw 600mA of filament current each so three of them totals out to 1.8A of filament current which the stock power transformer simply can't handle. If your using one of the Triode Electronics or DynaKit Parts replacements then your fine. Actually the original ST-70 specified 1A of available filament current per winding for the PAS preamp that connected to the front socket jacks. If this was true would make this board usable in a stock amplifier, however they were a little ambitious with these specs so don't try it. Don't say I didn't warn you. If you really want to use the board and don't want to upgrade your power transformer there are still options. You could install a separate filament transformer to run the board's filament supply. Hammond has some nice 6.3VAC @ 2A filament transformer that you can pick up for about $15. In fact if you don't use the power take off sockets (most people don't) then you could easily make a separate unit to house the 6V transformer and rewire the power takeoff sockets on the amplifier to accept power from the external unit. Triode Electronics sells the 78S8 and 86CP8 octal plug and sockets you would need to make the connector cable.
