Opto to bias triode?

[jackinnj]

LED's are great, but come in limited VF/

Again, picking up on Scott's G=1,000 amplifier which uses the Vishay VO1263 optocoupler, one could use two to match the triode halves. VO1263 transfer function is around 1/1000

 

[BinaryMike]

VO1263 output tolerance seems to make it unusable for grid biasing unassisted. One might consider using the difference voltage between two Zener diodes, but I worry about noise and insufficient bias current in those Zeners.

 

[jcx]

why not run the LED at higher current?

few mA wouldn't give too much ageing, higher output current gives less noise, less effect from leakages in C, board

and using the PV diode output current to bias a LED as shunt ref will give some regulation

 

[BinaryMike]

With a maximum of maybe 30uA guaranteed output current, I dunno about stabilizing bias with LEDs. The good ol' LM385-ADJ voltage reference works down to 10uA and could be noise-filtered easily, so maybe that's a good option.

 

[6A3sUMMER]

What are you trying to build, a matched gain 2 channel preamp?

What signal source will you use, phono cartridge, CD player, etc.?
(How much input signal voltage do you have?)

How much output voltage do you need?

The above schematic is a mystery to me.
Also, a reference to Scott's G=1000 amplifier does not include a link to it.

 

[Wavebourn]

Use LEDS of optocouplers in cathode, may be you can get even better results. ;-)

 

[KSTR]

http://www.diyaudio.com/forums/grou...1000-low-noise-measurement-amp-ikoflexer.html
The control loop idea is brilliant but won't work without major redesign, for triode.

 

[jcx]

why not?

at least for this tube it looks like O 100 nA grid leakage at typical ~-1 Vbias given the graphs with 10 Meg grid leak bias

so the "opto diff amp" servo Scott shows would have enough "authority" if you wanted ~ 1 mA in the tube, would then have ~ 1 uA in the opto PV

 

[jackinnj]

Build it and see.

 

[jcx]

I just want to know the reasoning - I have no intention of building with tubz

 

[stocktrader200]

Jcx , you cannot get the sound of tubes without tubes, I am a SS guy first and foremost.
I designed a 3 transistor 3 tube amplifier that can't be beat by Silicon alone.
I gave up and and now have 6922 tubes in my equipment. I won't be going back to SS alone.
The band sounds like it's in the room. By the way a 6922 tube can be had for less then $10