Adjusting the sensitivity on a 6e2 magic eye tube

bbbing · 15th October 2009, 11:04 AM

Hi there

I have a yaqin 5881 tube amp (schematics attached). I have done a few mods ie change the coupling caps and re-wire the output to triode. Does anybody know how to mod the magic eye tube / circuit so the peak level indicator displays at lower volumes?

I have tried shorting the 10k resistor from the 8ohm output tap. That increases the sensitivity a little however the volume still needs to be quite loud for the indicator to move. Any suggestions would be appreciated.

HollowState · 15th October 2009, 02:54 PM

Perhaps replacing that standard 1N4148 silicone diode with a more sensitive type like a schottky or even a germanium would help. Reducing or removing the .1ufd cap after the diode could also help. It's there to smooth out the rapid fluctuations of the signal and give a more stable indication. Of course you'll loose the intended purpose of a peak indicator.

kevinkr · 15th October 2009, 04:12 PM

Another possibility would be to take the drive for the 6E2 from one of the output tube plates and capacitively couple it and pad it down substantially. You could use a 100K resistor and 10K pot and this would give you a substantial adjustment range. Use a 2W resistor, and 1kV film or ceramic cap of about 0.022uF - 0.047uF or so.. And be careful as the ac + dc voltage components present with signal applied could be 700V - 1kV at full power depending on supply voltage. (Figure up to 2X the supply voltage at the CT of your OPT and you get the picture.)

Wavebourn · 15th October 2009, 04:31 PM

Use 2 small Shottky diodes as a voltage doubler.

JimTube · 21st May 2010, 07:28 PM

Quote:

Originally Posted by bbbing

Hi there

I have a yaqin 5881 tube amp (schematics attached). I have done a few mods ie change the coupling caps and re-wire the output to triode. Does anybody know how to mod the magic eye tube / circuit so the peak level indicator displays at lower volumes?

I have tried shorting the 10k resistor from the 8ohm output tap. That increases the sensitivity a little however the volume still needs to be quite loud for the indicator to move. Any suggestions would be appreciated.

Hi bbbing,

did you get any good results increasing the sensitivity of the 6E2 tubes. I have the same amp and i tried a lot to make the bars gone @ normal volume settings. I hope you have found a way :-)

Regards ... Jim

15th October 2009, 02:54 PM	#2
HollowState diyAudio Member Join Date: Aug 2006 Location: Taxland, New Jersey	Perhaps replacing that standard 1N4148 silicone diode with a more sensitive type like a schottky or even a germanium would help. Reducing or removing the .1ufd cap after the diode could also help. It's there to smooth out the rapid fluctuations of the signal and give a more stable indication. Of course you'll loose the intended purpose of a peak indicator. __________________ "The supercomputer is technologically impossible. It would take all of the water that flows over Niagara Falls to cool the heat generated by the number of vacuum tubes required." ~ Professor of Electrical Engineering, New York University

15th October 2009, 04:12 PM	#3
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	Another possibility would be to take the drive for the 6E2 from one of the output tube plates and capacitively couple it and pad it down substantially. You could use a 100K resistor and 10K pot and this would give you a substantial adjustment range. Use a 2W resistor, and 1kV film or ceramic cap of about 0.022uF - 0.047uF or so.. And be careful as the ac + dc voltage components present with signal applied could be 700V - 1kV at full power depending on supply voltage. (Figure up to 2X the supply voltage at the CT of your OPT and you get the picture.) __________________ www.kta-hifi.net

15th October 2009, 04:31 PM	#4
Wavebourn diyAudio Member Join Date: Sep 2006 Location: Pleasant Hill, CA	Use 2 small Shottky diodes as a voltage doubler. __________________ The devil is not so terrible as his mathematical model! Wavebourn: We Create Creativity!

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