Biasing EPJ

[Steven1281734009]

1. R14 =240R

2. Cathode Voltage=10.21V

3. Anode to Cathode Voltage 302.2V

4. Cathode Current .043A

5. 12.86W

6. 10% of Cathode Current 1.3

7. 11.56 Dissipation

 

This is what I got by following the directions at : http://www.diycustomamps.com/valvejunior.htm#vjbias

Did I do it correctly, and if I did, am is this good enough or can it be improved?

 

Thanks,

 

Steven

[tunghaichuan]

Looks fine to me. The only caveat is that if your line voltage fluctuates, it might push the tube over the 12W dissipation limit. Personally, I like to have my amps biased a little bit lower than the max just in case my line voltage goes up.

 

tung

 

 

1. R14 =240R

2. Cathode Voltage=10.21V

3. Anode to Cathode Voltage 302.2V

4. Cathode Current .043A

5. 12.86W

6. 10% of Cathode Current 1.3

7. 11.56 Dissipation

 

This is what I got by following the directions at : http://www.diycustomamps.com/valvejunior.htm#vjbias

Did I do it correctly' date=' and if I did, am is this good enough or can it be improved?

 

Thanks,

 

Steven

[/quote']

[Steven1281734009]

To make it a little lower would a 250R do the trick? I am not sure if the line voltage fluctuates but it is a little high at about 123v. Would a power conditioner or variac work too? I know it certainly sounds better now that I changed R14 from 220R to 240R. I also seen on the S2 website that a 20 Ohm 20W power resistor on one of the primaries was used. Can this help improve things? What does it do?

 

Thanks

 

 

Steve

[tunghaichuan]

I usually use a 270 ohm, 3W metal oxide resitor in my VJ amps. The only place that I've found that has 250R resistors is Antique Electronics Supply. My amp biases to about 10.5-11w depending on what my line voltage is. Close enough for me. OTOH, don't make yourself crazy over this. EL84s are fairly inexpensive.

 

The 20 ohm, 20W power resistor knocks down the line voltage going into the PT. Since the PT is spec'd for 115 operation, and the line voltage is 120v+ in most of North America, it might not be a bad idea to put one in. The real advantage would be lowering the voltage to your filaments. The farther away the voltage is from 6.3v, the shorter the life of the tube. Although, the spec is + or - 10%.

 

tung

 

 

To make it a little lower would a 250R do the trick? I am not sure if the line voltage fluctuates but it is a little high at about 123v. Would a power conditioner or variac work too? I know it certainly sounds better now that I changed R14 from 220R to 240R. I also seen on the S2 website that a 20 Ohm 20W power resistor on one of the primaries was used. Can this help improve things? What does it do?

 

Thanks

 

 

Steve

[Steven1281734009]

I was not too worried about the cost of the tubes but was wondering if it would sound better if I lowered the bias even more. If I use the 20R, 20 watt power resistor on the primary, would it change the bias just like changing R14? and would it lower the voltage on the filaments?

[tunghaichuan]

To tell the truth, I don't know if I could detect a VJ operating at 10w vs 11w. I don't know that it would sound different at all. I view it as mainly a reliability thing.

 

Anytime you change the the overall voltage levels in your amp, the bias changes. At the very least you should check it. Adding the 20 ohm, 20w resistor should drop your filament voltage levels. How much depends on how much voltage drop occurs across the resistor.

 

tung

 

 

I was not too worried about the cost of the tubes but was wondering if it would sound better if I lowered the bias even more. If I use the 20R' date=' 20 watt power resistor on the primary, would it change the bias just like changing R14? and would it lower the voltage on the filaments?[/quote']