6V6 line preamp

[Salas]

Can be calculated from Vout pin - Vh but that's including cable voltage drop. Anyway what you aim at is correct Vh.

 

[merlin el mago]

-7.64V

 

[Salas]

What voltage between LM317 pins 1-2 directly?

 

[merlin el mago]

Oooops sorry Salas correct VRef is 1.2417V

 

[merlin el mago]

Now with the same reg. I will test the other tube filaments

 

[merlin el mago]

The other tube 6.375V

 

[Salas]

Perfectly OK for both tubes we can say. Takes ~45sec to light up fully?

 

[merlin el mago]

I didn't measured the time but I think more.

 

[merlin el mago]

I'm goig to see if I have 3.3 ohms parallelled with 16 Ohms at only -0.16 % out.

 

[Salas]

Oooops sorry Salas correct VRef is 1.2417V

You may find closest Vref match between your LM317s if to keep measured resistors exactly the same value between dual heater psus or you will match tolerances between LM317 sample and Rset. If you care to have close Vh between certain tubes which is not very necessary.

 

[Salas]

I didn't measured the time but I think more.

Probably a minute

 

[merlin el mago]

I have 5W each

 

[merlin el mago]

Probably a minute

More or less

 

[Salas]

During this time you don't have the power amp on because the 6V6 stage is stabilizing. And you turn off the power amp first during system shut down. Alternatively you use 1 minute or more on time delay / fast off 6V6 line signal output relay system.

 

[merlin el mago]

Schematic pls? How to implement?

 

[merlin el mago]

I always power the system starting first the source & final the power amp and turn off inversely.

 

[Salas]

Schematic pls? How to implement?

I don't have my schematic. Must design if I ever need. Simplest would be copy from dcg3 and make big value R for RC. I just power on & off in the sequence you described. There are 555 chip based solutions with variable timing etc. Just Google and you will find.

 

[merlin el mago]

OK, just remembered Erno Borbely used in his pre-amp.

 

[merlin el mago]

It seems isn't enough with 3R3 paralleled with 16R, I have to reduce still more the resistance.

1.2417VRef / 2R74 = 0.453A

 

[Salas]

Six Volt DC is good for longevity. In my original schematic I had 3.3R parallel to 15R. Possibly for 6.1V. Can't remember.