Updated: 24-Jan-01
The (optional) Tube stage, which adds gain and low Output impedance to drive Main Amps

It is recommended to download first the PDF Document DDDAC1.pdf with the schematics.
For pictures of all the parts please see the Technical Backgrounds Section and Picture Galery

picbks24.jpg (5327 bytes)
The MU Tube stage built on a Eurocard PCB, hardwired

FIRST OF ALL: At this point I like to thank Dick van der Merwe, who supported me on application and development of the so called MU stage.. Dick is a Tube wizard and his work can be found on www.triodedick.com   Please visit him and get as enthusiastic as I became!!!! Without people like Dick, Tube life hasn't been half as exiting as it is now.....

Basically the MU stage is a great line stage or driver stage because of the following "features"

  1. Full mu gain, because the Triode sees a virtually infinite Plate resistor, the Triode swings complete un constrained at constant current
  2. Very low output impedance, capable of driving difficult and or long cables
  3. "High" current output capability coming from the current amplifying Penthode, resulting in higher bandwidth and no slew rate problems
  4. Extremely stable auto adjusting circuitry. The MU finds its own working point very easily. As tubelife goes one, no problems to expect

Actually, you can build a MU stage with every triode for voltage gain, but here you can make actually unlimited use of the extreme nice linear voltage transfer characteristics of the "older" triodes, like 30, 27, 57, 76, 227 etc. Normally these triodes are difficult to use because of low mu and high plate resistance and low transconductance. But looking at the above, you now can, so why use the little tubes, like ECC stuff, which are absolutely less linear and have more uneven harmonic distortion (therefore they sound more like transistors compared with the old fashioned triodes

All values in the schematics are real measured values. Even when I change the tubes to new ones (unfortunately I started with "used" tubes, which had quite some hummmmm), the values stayed just the same (!!!) Also important with he direct heating is, the floating supply. I used a constant current source here, for optimal performance. With the potentiometer you can adjust at 2.00 Volt. The filament can also be fed by an battery, but this is always more complicated with the charger etc. The choice is free.....



IMPORTANT: The information provided on this page is intended as guide for DIY activities and therefore free to copy and or publish. If any one wishes to use any of the information from my WEB site, please make sure to refer and footnote to my URL Link as source! Doede Douma