Complications of using 2c22/7193's on ST-70 Driver Board?

[primosounds]

Ehm, I didn't say I'm looking for something with objectively superior output and measurements, nor did I imply as much. To say " something rethought entirely to sound far better than the original " is exactly what it sounds like, a design that the creator had invented with the purpose of creating something that sounds better. If I myself claimed it to sound better that's one thing, but in this context there was no such implication. I only observed that the action of using a modification created with the mindset of a better sounding driver board would be perhaps worth a shot before a substitution for the original.

If you want to try something different, that many dynaco afficionados are not familiar with, check out the K&K Audio mod which involves using Lundahl splitter transformer instead of a tube phase splitter. Here is the link for your perusal. Per requirements, i am not affiliated with K&K audio , blah blah blah, yada yada yada.
http://www.kandkaudio.com/power-amplifier/
But, if i were trying to achieve something different with a Dynaco ST70 and did not want a circuit board or spending a lot of money on a kit, the K&K costs more than most if not all of the Dynaco mods sold commercially, I would rather build a different driver/splitter circuit. One such is the EICO HF87 / 89. It uses the 'long tailed pair' phase splitter employing a 12ax7 input and 6sn7 or 6cg7 as the splitter tube. Since the input tube is directly coupled to the 6sn7 there is no inter stage coupling cap which has audio benefits. IMO, and many tube fanatics too, the sound quality of the EICO HF87 in stock form betters the Dynaco on its best day. Part of that is because of the front end circuit. I don't know if any of the Dynaco circuit board suppliers do that type of front end but that might also be worth checking out. cheers.

 

[gadget73]

The LTP with a single triode driving it is basically the Mullard circuit. Pretty sure thats what the 3 12AU7 board gives you. One triode in the center tube per channel as a voltage amp, both triodes in the outboard tubes working as the LTP inverter. You can get the same thing done with 6SN7, 6CG7, or really any combo that yields up 3 triodes per channel. If it mentions something about a constant current source, or CCS, thats almost surely a long tail pair inverter.

The original Mullard circuit actually ran an EF86 pentode as the voltage amp, and usually a 12AX7 as the inverter but the basic concept is the same. If you don't need the gain that the EF86 offers a triode does fine. I have actually triode strapped an EF86 to knock down gain before when removing tone controls from a Mullard 5-10 amp.