Wanting to do some DIY and remember my old Dyna ST-70 that had octal sockets on the front of the chassis. To set the bias you would fire it up, set it at 1.56 volts if I remember, and after it was good and warmed up, check it again and correct. There was a pot with a shaft made for using a flat headed screwdriver on to change the bias setting.
What I want to do it to mount some meters so I know what the bias is all the time. I plan on using 6V 2A3 types and would like to know the bias setting so I can look for the correct type of meters and pots.

Thatch

What is 6V 2A3?

The first thing is if your going to use 6A3's the B+ is way too high , it should be around 300 volts and the ST 70 more like 480 to 500 volts . If you use Russian 6B4G's it could get away with 400 volts . The bias volage sould be around -61 volts for 80 MA iddle current or 470 ohm for a shared cathode resistor . The output transformers are 4.2K ct in the ST70 so you will get about 8 to 10 watts output with fixed bias and 5 to 8 watts with a cathode resistor

Not sure if the OP is going to install the 6V 2A3 type tubes in the ST-70 or if the OP is goping to DIY an amp based around this tube and used the ST-70 as an example of the bias setup.

If the OP is going to use an actual ST-70 I recommend using the output tubes that the ST-70 was designed for.

Here is what looks like an easy digital VDC LED meter solution for monitoring the bias. https://www.youtube.com/watch?v=GBkL4FzArR8