6V6 line preamp

[Salas]

23mA seems spot on, -30V seems weird. I would expect 113V on the grid stopper after Cinput and 123V on cathode, 10-11V across the 470R for 300V B+. Approximately.

 

[gtoro]

There Was a mistake on cathode are 120v and 90 on grid i go to measure again.....

 

[Salas]

That sounds much closer, as tube makes and vintages differ.

 

[gtoro]

Ok i changed multimeter non i have:

Anode 295v
On the grid stopper after Cin 88v
On cathode 120v
8v across 470r

Actually i'm listening good music with this parameters...

The resistors are from schema standard the supply is a CRCRCRC doubled in the last for the Teo channel

 

[Salas]

Its a good point at 295V. Originally it was for 330V but not far.

 

[stajo]

On the grid stopper after Cin 88v

This value is odd though. Probably measuring fault. It should be the difference between voltage over 470R and cathode.

 

[gtoro]

This value is odd though. Probably measuring fault. It should be the difference between voltage over 470R and cathode.

May be, but there is a 470k between 470r and junction of Cin and 1k grid stopper

 

[stajo]

I guess it says that there is a small grid current, Otherwise there should be no drop over the 470 k.

 

[gtoro]

I guess it says that there is a small grid current, Otherwise there should be no drop over the 470 k.

It is true... I go to measure again...

 

[stajo]

Here is your approximate loadline and operating point. Voltage over 470R should be like 11 V.

 

[Salas]

This value is odd though. Probably measuring fault. It should be the difference between voltage over 470R and cathode.

I guess it says that there is a small grid current, Otherwise there should be no drop over the 470 k.

It is true... I go to measure again...

Slightly leaky input cap could also change the expected grid to ground voltage measurement.

 

[stajo]

Did anyone try to build or sim this without cathode bypass cap?

 

[gtoro]

Some update: Not time to built a decent box, but I listen it (in wood-wine box) for a long time, with russian 6v6 and rca in metal case (6v6y) the first was definetively better: wide and loud at least IMHO and in my temporary realisation, absolutely silent, take a permanent place in my system.

 

[stajo]

Noone maybe. Some superlocal fb w less amplification , lower thd and unfortunately some higher Z-out is worth a try. Z is ok as is

 

[Salas]

You know the story. 6dB less gain, double the Zo, half the 2ndH with about the same 3rdH.

 

[fdegrove]

Hi,

Noone maybe. Some superlocal fb w less amplification , lower thd and unfortunately some higher Z-out is worth a try. Z is ok as is

If you can live with the lower gain and higher Zout it may be worth a try if only to judge the sonic impact of the decoupling cap.

I usually prefer the sound without the decoupling caps especially in a (phono) preamp. But then it's best to design with that in mind from the onset.

Another workaround would be to replace the cathode resistor with an appropriate LED if you don't mind the sand.

Ciao, 😉

 

[stajo]

I did listen a while and I liked the cf best but that is only because it fitted my other gear. Right now I have no preamp.

 

[stajo]

You know the story. 6dB less gain, double the Zo, half the 2ndH with about the same 3rdH.

I do know the story. Bringing it up again. Its a love story

 

[Zen Mod]

no Miss Piggy

SLCF , or without it

 

[stajo]

ZM likes first order, I do like second order. A matter of taste.