New Rebel 30 tubes

flakeygeek2000

New member
I wanted to check the bias on my Rebel 30 Head.

The photos showing the bias test points and trimpots on the combo are super helpful.

To access these on the head, do I have to slide the amp chassis out?

I'm guessing that it the four screws on the bottom that I need to remove to do that, right?

Alan
 

3 Mile Stone

New member
flakeygeek2000":2zy4hk1c said:
I wanted to check the bias on my Rebel 30 Head.

The photos showing the bias test points and trimpots on the combo are super helpful.

To access these on the head, do I have to slide the amp chassis out?

I'm guessing that it the four screws on the bottom that I need to remove to do that, right?

Alan


Correct Alan. That's how you do it.
 

jdsjw13

New member
Thanks for the advice guys. I was actually saying that the volume is quieter on the "full on" 6V6 side than it is on the "full on" EL84 side....and yes, it is loudest at 12:00. It's not a huge volume drop off, in fact it is slight....it's just kind of annoying. When you turn up the volume on the 6V6 side the amp sounds great so I don't think that it is a problem with the actual tubes. That is why I thought that maybe they were just not biased the same or something.

Like I said, this is my first tube amp and I'm really interested in learning as much as I can. Do you guys have any links or resources to help me learn to check bias, re-bias, etc (other than the previous posts on this topic of course). It seems fairly simple once you know what you're doing. I just don't want to screw anything up with the amp or electrocute myself!! Thanks again
 

WIRED

New member
This looks so simple, I'd like to try doing it myself for my R30 head. My question is: I'm freaked out about all the "high voltage" warnings as far as removing the chassis. Which components in the chassis do I need to avoid touching to be safe? Is there anything exposed in there that will shock/kill me if I touch it accidentally?

This may seem like a dumb question to many of you, but I'm being serious. I'd really like to do this simple maintenance myself, but I want to be safe above all else.

Thanks for any help you can provide.
 

Len Rabinowitz

New member
To be safe, all you need to do is unplug the amp from the wall and then let it sit about 30 minutes. That will make sure that all residual power is gone from it. You can touch anything at that point.

:rock:
 

danelectro

New member
Leave the amp in the "on" position rather than "standby" and turn of the power switch on the backside of the amp. This should cause the caps to drain. Unplug the amp and if you want to play it safe, let it sit for 30 minutes
 

briguy73

New member
Really dumb question but I'm asking anyway...when you're biasing a Rebel 20 or 30, you do it with the power on, speaker(s) plugged in, guitar plugged in right? Or can you bias it while on standby? Or while it's off for that matter?
 

WIRED

New member
briguy73":3boy70j4 said:
Really dumb question but I'm asking anyway...when you're biasing a Rebel 20 or 30, you do it with the power on, speaker(s) plugged in, guitar plugged in right? Or can you bias it while on standby? Or while it's off for that matter?

From what I've seen/read, the amp has to be on (not on standby), & must be plugged into a speaker. No instrument needs to be plugged in. Let the amp warm up for at least 5 minutes to get accurate readings. I've also read that channel volumes should be at zero, but not sure how important that is.
 

briguy73

New member
For the benefit of those who are a little gunshy opening up they're Rebel 30, biasing my Rebel 20 was a cakewalk. I'm not a techy gearhead by any stretch (just don't go pokin' around ANYWHERE other than the testpoints and you won't end up with hair like Rod Stewart) Went to the shack and picked up a digital multimeter for 20 bucks. Owned my Rebel 20 for about a year. Haven't swapped any tubes, still has stock JJ's in the power and soveteks in pre. Interestingly, when I checked the bias, BOTH the 84's and the 6V6's were a tad on the cool side...about about 36mv on the 84's and about 40 on the 6V6's. Makes me wonder if power tubes have a bit of a break-in period. Made the adjustment in a matter of moments and a great amp sounds even a little better. Thanks for this thread and all the help. Egnater rules!
 

gregrjones

New member
Is there any significant danger of getting electrocuted if I try to set the bias when swapping out power tubes?

Are there any extra precautions I should take?
 

Ian Egnater

New member
gregrjones":2vbh8j60 said:
Is there any significant danger of getting electrocuted if I try to set the bias when swapping out power tubes?

Are there any extra precautions I should take?


There is always significant danger when you put your hands in a live amp. My honest recommendation is that if you don't know exactly what you are doing, then have someone knowledgeable help you out.
 

Len Rabinowitz

New member
You drain the voltage to swap the tubes and not kill yourself at the same time. Obviously, the amp has to be on to bias the tubes once they are in.

:rock:
 

gregrjones

New member
Len, forgive me for being a little slow but I think you're saying turn off the amp, drain the voltage, swap the tubes, then turn on the amp to check the bias. Correct?

If so, then I guess I this means that if you turn on the amp and the bias is off, this won't damage the amp?
 

Len Rabinowitz

New member
I am not an electrician, but yes that is what I am saying. I don't think the bias is ever "off." Do the power drain and tube swapping first. Turn the amp back on. Re-bias according to the instructions in the manual. There is no reason why a properly done re-biasing should damage an amp. It is a good thing to do every now and again even if you don't swap the the tubes because the bias can drift over time.
 

Razsan

New member
Hi guys...resurrecting an old thread. I'm a noob to biasing and just wanted some clarification.
Is this correct?
1 - Amp is on, no guitar plugged in
2 - touch middle TP1 with negative and either TP2 or TP3 with positive multimeter posts
(wasn't sure if this was the other way around)
3 - Adjust either TP2 or TP3 pot to 40V
The question is how do you adjust? do you turn by hand or use a flathead screwdriver in the middle of the Pot?
Thanks
 

Len Rabinowitz

New member
Flat head screwdriver. Check the manual because you often have to have the knobs set certain ways since they can influence the bias readings.
 

Razsan

New member
Len Rabinowitz":al1rphfz said:
Flat head screwdriver. Check the manual because you often have to have the knobs set certain ways since they can influence the bias readings.
Thanks Len...I appreciate the response!
 
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