Valve Itch phono

[Salas]

Not that crucial

 

[merlin el mago]

Could I use a couple for 5687 preamp in place of battery grid bias 3.3-3.6V?

YHPM

 

[Salas]

The infra Leds have very low impedance and low noise at little mA bias but they do need a current bias to produce voltage

 

[merlin el mago]

I want to use it between the cathode & ground?

 

[Salas]

As indirect bias through raising the cathode voltage it's ok

 

[merlin el mago]

Thank you Salas.

Salas can I use for Sic Cree C3D02060F in place of infrared LED? If yes 1 will be enough?

Attached data sheet of diode.

 

[Salas]

No, too big a diode to bias well with just mA. It will bring low Vf, much pF, and possibly unsteady. That's a part designed for working with Ampere level currents.

 

[merlin el mago]

Alex Moglia & Andy used for 01A & 26 preamps

 

[Salas]

It isn't something I would have an eye for in this use, but if used already by others it may have merit. Expect low Vf at mA bias though. Way below its nominal.

 

[merlin el mago]

Vf aprox. 0.8V each

 

[vgeorge]

Alex Moglia & Andy used for 01A & 26 preamps

The 26 has about 1 ampere in the cathode in filament bias, not mA.

 

[merlin el mago]

26 needs x12 diodes so each diodes passes 83mA

 

[vgeorge]

Are the diodes parallel???

 

[merlin el mago]

Are the diodes parallel???

 

[vgeorge]

Then do your math again.

 

[merlin el mago]

I'm not very good with maths

 

[vgeorge]

It would be 83mA if they were in parallel.
As they are in series every diode sees the same current as the filament.
Ohm' s law etc....

 

[merlin el mago]

26 runs 6mA, 1A is for heaters.

For Itch is cathode bias not filament bias.

Ale Moglia: The do operate well from low currents and impact on the increase of Rds is minimal. Running them at low currents (e.g 3-4mA for a 01a stage) provides no measurable additional distortion due to the lower operating point in the knee.

 

[vgeorge]

26 runs 6mA, 1A is for heaters.

For Itch is cathode bias not filament bias.

I give up

 

[merlin el mago]

I'm sorry if my ignorance disturbed you.