Author Topic: Reverse engineering a classic audio product?  (Read 737 times)

0 Members and 1 Guest are viewing this topic.

Offline cvancTopic starter

  • Frequent Contributor
  • **
  • Posts: 675
  • Country: us
Reverse engineering a classic audio product?
« on: February 21, 2020, 04:53:22 pm »
OK audio types, here's something you don't see every day...

Attached is the schematic for the Beveridge Electrostatic loudspeaker model 2SW-1.  Back in the day it was argued to be one of the finest speakers ever made.  Let's figure out how it works.

It has a built-in hybrid amplifier that uses tubes for the output stage.  The configuration is novel, allowing for transformerless drive to the transducer panels.

I would love to discuss how the output stage works.  Especially how does it bias the driver transistor pair, and how does the output node of the tubes stabilize at a quiescent state halfway between +HV and ground?  I am not visualizing it...

Thanks!
 

Offline duak

  • Super Contributor
  • ***
  • Posts: 1048
  • Country: ca
Re: Reverse engineering a classic audio product?
« Reply #1 on: February 21, 2020, 06:55:24 pm »
R1 & R3 look like feedback resistors to the driver stage.  A higher cathode voltage on V201 & V203 leads to more base current into Q108 & Q109 then Q110 & Q111 turning them on harder, pulling the grid voltages of V202 & V204 up causing their plate voltages to fall and bringing the cathode voltages back to nominal.  The actual voltage is a function of the voltage of the -60V rail and the values of the various resistors in the feedback circuit.

« Last Edit: February 21, 2020, 06:57:17 pm by duak »
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf