Rebiasing procedure for Rebel 20

[Retarius]

I have a new batch of 12AX&s, 6V6s, and EL-84s on the way from Dougs Tubes, and was looking for a rebias procedure for the Rebel 20? Couldn't find one on the Egnater site, in the User Manual, or here.

I haven't rebiased tubes before, so not exactly sure what to do. However, I am an electrical engineer and know my way around electronics and test equipment - so all is familiar once I know the procedure.

Thanks in advance,
Retarius

 

[jmgman69]

I have a new batch of 12AX&s, 6V6s, and EL-84s on the way from Dougs Tubes, and was looking for a rebias procedure for the Rebel 20? Couldn't find one on the Egnater site, in the User Manual, or here.

I haven't rebiased tubes before, so not exactly sure what to do. However, I am an electrical engineer and know my way around electronics and test equipment - so all is familiar once I know the procedure.

Thanks in advance,
Retarius

You have to take the chassis out of the head shell and there are 2 sets of biasing pots with little stands to put in a multimeter.and the milivolts are printed on the board next to it.I'll see if I still have pics.

 

[Retarius]

Stah,

Taking a look at it, I'm guessing this is the procedure:

1. Take amp out of case
2. Replace tube(s) - either 6V6s or EL-84s
3. Plug amp into AC
4. Hook up voltmeter - positive lead to proper test point, negative lead to chassis
5. Adjust pot until reading matches PCB silkscreen (45ma for 6V6, I think)

It looks like there are no test points, trimpots for the preamp 12AX7s, so guessing they don't need biasing>

Thanks,
retarius

 

[jmgman69]

Stah,

Taking a look at it, I'm guessing this is the procedure:

1. Take amp out of case
2. Replace tube(s) - either 6V6s or EL-84s
3. Plug amp into AC
4. Hook up voltmeter - positive lead to proper test point, negative lead to chassis
5. Adjust pot until reading matches PCB silkscreen (45ma for 6V6, I think)

It looks like there are no test points, trimpots for the preamp 12AX7s, so guessing they don't need biasing>

Thanks,
retarius

No bias for 12AX7s

 

[Retarius]

Thanks Stah!

 

[Audioholic]

do you really need to re-bias if you are replacing with the same type of power tubes?

 

[Buckeyedog]

do you really need to re-bias if you are replacing with the same type of power tubes?

Yes, most definitely. Some tubes are really hot, others not so much. You can't believe how much I have to turn my bias pot on my Mod 50 when swapping same type tubes.

 

[Audioholic]

do you really need to re-bias if you are replacing with the same type of power tubes?

Yes, most definitely. Some tubes are really hot, others not so much. You can't believe how much I have to turn my bias pot on my Mod 50 when swapping same type tubes.

makes sence, but you can order certain ratings of tubes correct? I have swapped power tubes (same type) and havn't rebiased without any adverse effects, so either I go lucky or just about the same matched tubes

 

[Buckeyedog]

Yes, you can use the Groove Tubes rating deal, but you need to make sure that whatever number you get is biased correctly from the start. Then you can just get "4"'s or whatever from then on out, but get that first set biased correctly.