Greetings!

807SE2

A Versatile SE 807 Amplifier
by Jeffery Larson
abraxasaudio


Index

8/2005


This, my second SE 807 amplifier represents my continued interest in Loftin-White type circuits and the marvelous sound they can make.





This particular amp was commissioned by Kevin. It is a quasi Loftin White in that the plate of the input tube is capacitively coupled to the output tube grid. I did this to save on power supply requirements. The input tube still receives its stabilizing voltage from the current running in the output tube cathode circuit. I hope soon to post the result of my extensive research into the Loftin-White design which includes information about the circuit, and explains why some amps that call themselves "Loftin-White" are not so.


I have to be brief in the description of this one as I have little time these days for my pages.

This amp has two mode of operation, both triode and pentode. In addition, there are two modes of input tube operation that give different tonalities. On the back there is a speaker impedance selector that allows the user to select the correct impedance for the operational mode and/or make adjustments allowing for a certain range of speaker impedances.

These switches and the associated circuitry make the amp's simple design appear complex when viewed from below.




The tube compliment is a 5U4, two 807's and a pair of 6EV5. The 6EV5 is a true tetrode and receives its screen voltage from the cathode of the the 807. It's two modes of operation are:
  • Linear, in which I keep the tube in its linear region and let the way it drives the output fall where it may.
  • Compensated, where I run the tube so as to help compensate in anti-fashoin, the output characteristic of the 807.

    Only high-performance caps are used throughout, and the coupling caps are a matched pair of vintage paper-in-oil types.

    The rest is just pictures for now.





    • Thanks for looking.
    Be sure to visit my other pages (see index above).

    Your comments are welcome.
    Critisms gracefully accepted.
    All questions courteously answered.
    Email to: abraxasaudio at att dot net
    (this avoids the address scanners)

    May I build one for YOU?
    jef