6V6 line preamp

[Salas]

I have 9VAC dual secondaries in my build, so its enough

 

[Salas]

I see 3.3R // 22R // 100R for Rset in mine, so 2.79R fine tune. You could put 2.8R 5W or your 3R high power rheostat. But is it connected as it should, and is its wiper OK?

 

[Salas]

The power tx is very hot

Weird

 

[merlin el mago]

What's the total power of your tx?

 

[Salas]

150VA if I remember correctly. Has 5V rectifier tube heater winding, dual 9V main tubes heaters wiring and 305+305V HV secondaries with mid point. Custom ordered locally.

 

[merlin el mago]

I see 3.3R // 22R // 100R for Rset in mine, so 2.79R fine tune. You could put 2.8R 5W or your 3R high power rheostat. But is it connected as it should, and is its wiper OK?

View attachment 1129838

Yes

 

[merlin el mago]

150VA if I remember correctly. Has 5V rectifier tube heater winding, dual 9V main tubes heaters wiring and 305+305V HV secondaries with mid point. Custom ordered locally.

Mine is a dual secondary 9VAC total 30VA so 15VA each secondary

 

[Salas]

Mine has 200mA HV. 3A rectifier heat, and 1A for each 6V6 heat. So 9VA each for 6V6. Weaker than yours for heaters only.

 

[Salas]

Do you have DC clamp meter to quickly check what kind of current runs in the wires?

 

[Lingwendil]

Silly question, but does your meter have a fresh battery in it? I was getting weird numbers a while back and a fresh battery made all well again. 😕

 

[merlin el mago]

No reason to not work like that. Unless there's a weird reason like an oscillation. For ease of mind put 0.1uF decoupling cap across DCin very near to LM317 pins

Could use 150nF? one pin to LM317 pin 3 DCin an the other to gnd right?

 

[Salas]

Of course. Not value critical. Yes, across DCin to GND.

 

[merlin el mago]

Silly question, but does your meter have a fresh battery in it? I was getting weird numbers a while back and a fresh battery made all well again. 😕

Replaced with a new one, but same measurements, BTW if battery low an indicator is displayed. Thanks.

 

[merlin el mago]

Setup pic

 

[merlin el mago]

It seems still oscillates

 

[merlin el mago]

Now all 30VA 9VAC to one LM317T

 

[merlin el mago]

Do you have DC clamp meter to quickly check what kind of current runs in the wires?

No

 

[Salas]

It looks like basically working. What voltage drop it now has across the rheostat pot? Maybe bcs of test leads being long, creating voltage drops messing with Vref, so it goes erratic. Try tight normal wiring.

 

[merlin el mago]

But as you can see at the rheostat the resistor value is very very low 0R1 máx 0R2, nothing similar to yours 2R7

 

[Salas]

That is not normal