The 1ohm Resistor Method for Biasing

[desertmouth90]

Does anyone have any diagrams for adding 1 ohm resistors for 4x6L6GCs on an Overdrive Special or something similar?

Also do I have to remove the original grounds pin 8 too?

thanks

[xtian]

You place 1R resistors between the power tube socket's pin 8 and ground. So yes, if pin 8 is currently connected to ground, you have to break this connection, and solder in the resistor instead.

[desertmouth90]

You place 1R resistors between the power tube socket's pin 8 and ground. So yes, if pin 8 is currently connected to ground, you have to break this connection, and solder in the resistor instead.

what if two of my 6L6s A and B are linked with a wire to pins 8?

[maxkracht]

If you want to measure your tubes in pairs, you can keep the link and use one resistor to ground per pair of tubes. If you want to measure individual tubes, which I would recommend, you need to one resistor per tube and no connections between them on pin 8.

[desertmouth90]

I used this, now it’s drawing too much current! And the bias isn’t normal on the output of the pot! Really weird

[xtian]

Adding the resistors will not change the existing bias. Post photos of your work.

[sluckey]

I used this, now it’s drawing too much current!

What's drawing too much current? Adding 1Ω resistors as shown will not affect tube current.

And the bias isn’t normal on the output of the pot! Really weird

What does this mean? Numbers please. The 1Ω resistors have nothing to do with the bias voltage.

[desertmouth90]

I used this, now it’s drawing too much current!

What's drawing too much current? Adding 1Ω resistors as shown will not affect tube current.

And the bias isn’t normal on the output of the pot! Really weird

What does this mean? Numbers please. The 1Ω resistors have nothing to do with the bias voltage.

I think I wired up the bias pot wrong


Before and after attached.

[desertmouth90]

Probes on the Ground and across the 1ohm resistors aren’t showing anything…

[B Ingram]

I used this, now it’s drawing too much current!

Before and after attached.

It looks like you're using Pin 1 as a mounting point to hold the grid stopper resistors running to Pin 5.

Your diagram here shows the grid stopper resistors going straight to Pin 5, with no connection to Pin 1. You must do it that way, or you ground your Bias Voltage, put 0vdc on the control grids, and send the output tubes into meltdown.

[desertmouth90]

I thought on a 6L6 pin 1 doesn’t do anything?

Since I reversed the 27k resister and -ve bias voltage lugs there is no buzz.

[sluckey]

It's OK to use pin 1 as a tie point for the 1.5K grid resistor. Thousands of Fender amps can attest to that. BUT!!! Pin 1 cannot also be connected to pin 8! Remove any jumper between pin 1 and pin 8. And connect the 1Ω resistor directly to pin 8.

Looks like you forgot to solder the grid resistor to pin 5. And every solder joint in the pic looks terrible. Not gonna be reliable if all your solder connections look like this.

[sluckey]

I thought on a 6L6 pin 1 doesn’t do anything?

It doesn't. but your little layout shows pin 1 jumpered to pin 8! YOU CANNOT CONNECT PIN 1 TO PIN 8 AND ALSO USE PIN 1 TO MOUNT THAT 1.5k GRID RESISTOR!

Depending on how long your amp was turned on you may have destroyed the output tubes and output transformer. 10 seconds may be a killer.

[desertmouth90]

I thought on a 6L6 pin 1 doesn’t do anything?

It doesn't. but your little layout shows pin 1 jumpered to pin 8! YOU CANNOT CONNECT PIN 1 TO PIN 8 AND ALSO USE PIN 1 TO MOUNT THAT 1.5k GRID RESISTOR!

Depending on how long your amp was turned on you may have destroyed the output tubes and output transformer. 10 seconds may be a killer.

I didn’t do that jumper… I kept them separate.

[desertmouth90]

It's OK to use pin 1 as a tie point for the 1.5K grid resistor. Thousands of Fender amps can attest to that. BUT!!! Pin 1 cannot also be connected to pin 8! Remove any jumper between pin 1 and pin 8. And connect the 1Ω resistor directly to pin 8.

Looks like you forgot to solder the grid resistor to pin 5. And every solder joint in the pic looks terrible. Not gonna be reliable if all your solder connections look like this.

It’s a fair point, I used awful solder on this project. But however I will be rebuilding it at some stage. The idea is to get it working first