New to X100 with tube rectifier. Tests and experience +mods coming

[MaciekP]

Hi,
some of my experiences to share:
http://diytriode.blogspot.com/2019/03/wzmacniacz-lampowy-fisher-x100-ca-1961.html

Right click on text in Chrome to translate...

 

[dcgillespie]

You would not want to pass a 10 kHz square wave through the tone section, as it does not have the necessary response (ideally flat to 100 kHz) to properly display the waveform. Instead, insert the 10 kHz square wave directly into the power amp section at the top of the volume control (with that control turned up full). That will then give you an accurate display of the power amplifier section transient response.

For the tone section, square waves of 2 kHz and 200 kHz are much more useful, as these waveforms will require flat response from 20 Hz to 20 kHz for proper display, and also allow you to properly center the controls for best flat performance as well.

Welcome to AK, and thanks for sharing!

Dave

 

[fred soop]

If tone controls are not centered, any square wave response will be a mess. The harmonics will be boosted or attenuated and have phase shift from the fundamental. Same for a loudness circuit.

 

[MaciekP]

You would not want to pass a 10 kHz square wave through the tone section, as it does not have the necessary response (ideally flat to 100 kHz) to properly display the waveform. Instead, insert the 10 kHz square wave directly into the power amp section at the top of the volume control (with that control turned up full). That will then give you an accurate display of the power amplifier section transient response.

For the tone section, square waves of 2 kHz and 200 kHz are much more useful, as these waveforms will require flat response from 20 Hz to 20 kHz for proper display, and also allow you to properly center the controls for best flat performance as well.

Welcome to AK, and thanks for sharing!

Dave

1kHz is a standard freqeuncy for measures.
Tone controls were on ZERO.
I will retest on monitor input which bypasses one triode.

At least "normally" via RCA socket input you would not bypass tone control. Monitor input is after high and low filter but before tone control:

 

[MaciekP]

I have added content regarding external bias control and distortions on 4V DAC output-X100 input.

 

[dcgillespie]

Maybe there was a problem with the translation. On my end, it indicated (I believe) that you were trying to pass a 10 kHz square wave through the tone control section, which it will not pass properly.

Dave

 

[MaciekP]

You can,t bypass tone control, but i have noticed that if you set treble to -1.5 square wave is almost perfect at 1khz. The other problem i noticed is with input voltages. Typical todays voltages are too high for this amp and cant be compansated with volume control as it is in the middle of signal path, so only monitor input with 500mV sensitibity is suitable for modern sources. I have repated the frequency plot for 400mV rms input where the previous one was done for 2V rms and was not very flat.