Was converting a amplifier to pentode operation from ultralinear. I removed the ultralinear taps, hooked up a resistor value of 1k to each g2 of the el34. Hooked those resistors to my first point of voltage in the amplifier after the power transformer. It makes sound and sounds okay. Except the tube is only drawing 15 ma of current. What should I do? Would it help to lower the g2 resistor? Since plate current and g2 current are related I believe

 

I'm sure it's a resistor value issue. I should make sure that g2 is within spec. What would be the proper way to calculate screen current?

 

What would be the proper way to calculate screen current?

Measure the voltage across the 1K resistor under "no signal" conditions.

I have found that copying Other Peoples' resistor value doesn't work because there will always be something different about my circuit. The only way to get it right is try something and measure the results, then do it over until you get it right.

 

Measure the voltage across the 1K resistor under "no signal" conditions.

I have found that copying Other Peoples' resistor value doesn't work because there will always be something different about my circuit. The only way to get it right is try something and measure the results, then do it over until you get it right.

Just did. 0 volts. This doesn't make sense. So. At the capacitor, I measure about 490 volts. I ran a wire from that cap to a terminal where I put bridged 2 500 ohm resistors. It's sloppy right now excuse that please. Follow the white wire.i just don't get how I have 0 volts. I am new so I probably probably made a stupid mistake. After all you have helped lotS.

 

Looks like your 1K is on pin 3, but I forgot which tube you're using.

It looks like your white wire is connected to the negative end of that capacitor...which should be ground!

Wait...a pair of 470's on pin 2. Without a tube number, I am getting lost, fast.

If I'm numbering the pins backwards, I will figure that out right after I know the tube number.

 

Looks like your 1K is on pin 3, but I forgot which tube you're using.

It looks like your white wire is connected to the negative end of that capacitor...which should be ground!

Wait...a pair of 470's on pin 2. Without a tube number, I am getting lost, fast.

If I'm numbering the pins backwards, I will figure that out right after I know the tube number.

El34. plate wire is right below it. And the end of the capacitor with the ridge is the Positive side. Arrows point to negative do they not. The resistors are all on pin 4 I just checked

 

It's just so difficult to see the pin labels in that photo.
Oh! It's an axial capacitor.

The resistors are all on pin 4 I just checked

It sure doesn't look that way. It looks like the (2) 470's and the 1k are on consecutive pins.

9 pin miniature, counted clockwise from the bottom, starting at a missing pin. Where's the missing pin?

 

It's just so difficult to see the pin labels in that photo.
Oh! It's an axial capacitor.

It sure doesn't look that way. It looks like the (2) 470's and the 1k are on consecutive pins.

I checked aha. Pin 4. Pin 3 is plate and the plate wire is going there. Where do I go from here. Why 0 voltage?

 

It just makes no sense why I'd have 0 volts. Except. When I measure from g2 to ground I get 490v

 

This Thread is turning into scrambled eggs. Take a 5 minute break. Sit down. Shut up. Trace everything, and catch any solder blobs while you're in there. The only way to break this is hard work and tight focus on the wiring.

 

This Thread is turning into scrambled eggs. Take a 5 minute break. Sit down. Shut up. Trace everything, and catch any solder blobs while you're in there. The only way to break this is hard work and tight focus on the wiring.

Okay. I checked all connections and they are good. I have 495 volts across the capacitor. Any wire running off the positive side get 0 volts. I am measuring I think by putting my leads on the positive side of the capacitor and the other end of the wire connected to the positive side. However this is true for all other capacitors also. I feel like I am measuring incorrectly. The issue is between the capacitor and the point at which I hooked it up to the resistors. Which is only a wire so I am not sure where to go from here. I am doing something incorrect I am sure.

 

Just did. 0 volts. This doesn't make sense. So.

If the screen grid is at 400vdc or less (with a >500 B+) there should be no or very little screen current at the quiescent signal position (increasing signals means increasing screen currents), no current flow means no voltage drop across the screen resistor. The resistor is there to limit screen current at full power.

 

I am measuring I think by putting my leads on the positive side of the capacitor and the other end of the wire connected to the positive side.

There is not supposed to be any voltage from one end of a wire to the other end. The voltage is compared to ground. Put the black probe on a ground point.

 

If the screen grid is at 400vdc or less (with a >500 B+) there should be no or very little screen current at the quiescent signal position (increasing signals means increasing screen currents), no current flow means no voltage drop across the screen resistor. The resistor is there to limit screen current at full power.

There is not supposed to be any voltage from one end of a wire to the other end. The voltage is compared to ground. Put the black probe on a ground point.

Okay, so it is normal for that to be happening. Sorry, still learning. since g2 and plate are tied and the plate is only drawing 15ma, how can I calculate the proper g2 resistor value

 

Okay, so it is normal for that to be happening. Sorry, still learning. since g2 and plate are tied and the plate is only drawing 15ma, how can I calculate the proper g2 resistor value

First it needs to be connected to a well regulated voltage source of usually less than the no signal plate voltage (or directly tied for triode operation) but not more than the rated screen voltage for the tube type. The actual resistance is not that important, 470 ohm to 1K ohm is typical. Higher values cause more voltage drop at full power with added gain for a compression effect because the screen voltage controls gain while unstable screen voltages cause intermodulation distortion.

I think that right as it 's been a long time since I've worked on tube audio amps.

 

First it needs to be connected to a well regulated voltage source of usually less than the no signal plate voltage (or directly tied for triode operation) but not more than the rated screen voltage for the tube type. The actual resistance is not that important, 470 ohm to 1K ohm is typical. Higher values cause more voltage drop at full power with added gain for a compression effect because the screen voltage controls gain while unstable screen voltages cause intermodulation distortion.

I think that right as it 's been a long time since I've worked on tube audio amps.

What could be the reason for the sudden drop in current pull from the output tubes. I have a new output transformer and even with the bias pot on full, I'm only drawing 11ma when I should be at about 37ma. plate voltage about 500v. Even more odd, the v drop from the center tap to plate is 70mv on one tube and 190v on the other

 

I don't feel like it could be the rectifier tube. Any thoughts?

 

Bump. What causes issues with b+ current? Rectifier? It's really the only component I could think of replacing in the b+.

 

Bump. What causes issues with b+ current? Rectifier? It's really the only component I could think of replacing in the b+.

I've got 590 v on each tube but one is drawing twice as much current. Doesn't make sense. Current is still too low