electronic industries

Tube stereo power amplifier.

The Electronic Industries ST-70 C2 was the second amplifier on the Dynaco ST-70 modification series. It was manufactured by Electronic Industries at 2451 Hennepin Avenue S in Minneapolis, Minnesota. The Electronic Industries ST-70 C2 took the original Electronic Industries ST-70 C1 and made improvements which resulted in better performance. Some of the improvements included:

  1. Added a heavy duty speaker terminal connection.
  2. Replaced the octal plug on the front panel with a filler plug. The octal plug was entirely removed from the chassis.
  3. Upgraded some of the parts on the Electronic Industries PCB-14 mother circuit board. This circuit board was used in all three versions of the Electronic Industries ST-70.
  4. Upgraded parts and capacitors inside the chassis.
  5. Added black plastic labels to identify the amplifier. This labeling system was also used in other early Electronic Industries designs like the Dual 50 and Dual 100 amplifiers.
  6. Upgraded the volume pots on the independent left and right volume controls on the back of the amplifier.

The amplifier came from the factory with high quality Mullard EL-34 output tubes and Telefunken and RCA input tubes. These amplifiers were produced in very limited quantities; more than likely less than 100 amplifiers were produced. The amplifier was available direct from the factory; no kits were sold to the public. Historically, this was the first revision that was ever offered to the public for an Electronic Industries product. An owner of the Electronic Industries C1 amplifier could have their amplifier upgraded to the C2 status for a marginal fee. William Z Johnson built or upgraded most of the Electronic Industries ST-70 C2 amplifiers himself.





MSRP (US new retail)


Power output  
Power bandwidth  
Frequency response  
Input sensitivity  
Input impedance  
Output taps  
Output regulation  
Overall negative feedback  
Damping factor  
Slew rate  
Rise time  
Hum & noise  
Power supply energy storage  
Power requirements  
Tube complement (2) OA2, (2) ECC-83, (4) 6FQ7 or 6CG7, (4) EL-34, (1) 5AR4 or GZ34