• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Wanted Radford MA-15

EC8010

diyAudio Moderator Emeritus
2003-01-18 7:57 am
Near London. UK
That's a pity about Woodside. You're right, a stereo amplifier with identical components in each channel has a much better chance with your LS3/5a. If I remember correctly, the STA15 was cathode bias, and the STA25 was grid bias. My LS3/5a appreciate a grid bias amplifier - it cleans up the bass.
 
EC8010
Just found your thread - interesting...

I have two Woodside MA100's.
The bias (grid adjusted) is set for 120ma across a 1.2R (2.5W) cathode resistor, which equates to -59v on the grids. If I grounded the cathodes and brought back the grids to -59v, am I likely to improve the bass resolution, or am I missing something?

Regards
 

kevinkr

Administrator
Paid Member
m1ke said:
EC8010
Just found your thread - interesting...

I have two Woodside MA100's.
The bias (grid adjusted) is set for 120ma across a 1.2R (2.5W) cathode resistor, which equates to -59v on the grids. If I grounded the cathodes and brought back the grids to -59v, am I likely to improve the bass resolution, or am I missing something?

Regards

This resistor is just a current sampling resistor, cathode bias's big shortcoming is the cathode bypass capacitor and a tendency to head towards class b operation when pushed hard. Neither of these issues are a problem with a 1.2 ohm resistor and your fixed (grid) biased amplifiers. I'd leave them alone as it is a convenient way to measure and set the bias and its value is low enough that it is extremely unlikely to have an audible effect.