Rig-Talk

So I bought a new Rebel 30 head. The tone lacks definition. Notes are buzzy, muddy and have no clarity. Following a thread on this forum, I replaced all the tubes and have attempted to do the bias myself.

The bias pots had a huge glob of white putty around them, securing them to the board (what I took to be the factory setting). I've never seen anything like that. Is this normal? Not being able to get through to support, I decided to carefully scrape that away and proceed (took a while).

I plugged in a speaker, turned it on (warmed up 10 min), set to play, and set the tube mix knob to full EL84. I placed the multimeter probes in TP1 (black) and TP2 (red) and got a reading of .036. I turned TP2 just a little and got no change in the reading. I turn it more. Still no change. I eventually turn it (with ease mind you) more than 360 degrees. Still no change. Same thing with the 6V6s, except they are stuck at .037.

I had the same problem setting the bias on the original tubes. They were off a little, but I couldn't get the setting to change, no matter how much I turned the pots.

How much do these pots need to be turned to see a change? I've spun them 5 full revolutions...Nothing! Any ideas?

Any help is appreciated.

First, curious what your issue getting through to our service was? Just message me that info, and I'll pass it on to the right place. Second, I can walk you through the bias process, but I believe the bias pot may now be broken, as it is only designed to turn one full turn. I have attached a pdf of the Rebel 30 bias process to this post, so I'll refer to that. Turning the tube mix knob will do nothing when adjusting the bias. Make sure when the amp is in play, that all the knobs on the amp are turned completely down first. The next few steps are on the drawing I attached, but basically you want to put the negative(black) meter lead in TP2, and the positive(red) meter lead in TP1. You will use the VRB1 adjustment pot when you are using TP1 and TP2 test points. You will then switch the positive meter lead to TP3 and use the VRB2 adjustment pot. You want the settings to read .040Vdc, +/- .004Vdc. If this still does not change your bias readings, then it is likely the adjustment knobs are overturned and possibly broken. You can message me if you have any more questions. Hopefully this all helps.

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Ian,

I can't ding your support, since I didn't leave a call back number.

Thanks for the PDF and the quick response. Consider this issue closed. I'm an idiot. I was turning the TP2 and TP3 test point plastic sleeves! They turned easy, so there is no damage. VRB1 and VRB2 work as specified.

Regards

Ian thanks for the pdf!

This is a first, but this is how some learn,but be careful,this thing can light you off like Fourth of July brother!!!!

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(Muy Guapo)
(Jason)aka UB thanks Kevin

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Ian, nice response and fast. It is really nice to see the first response to a problem thread be a rep of the Eganater brand. Good going dude. We appreciate that around here.

Dovetailing off of this discussion...I'm kind of green when it comes to biasing an amp.

Why is it done in the first place?

What is the Rebel 30 typically biased at, and how would changing it affect the tone?

Thanks!

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It adjusts the tubes voltage level.
Typically running volts low will increase tube life, but may make the amp sound dull or harsh.
Running tubes slightly hot might make the amp break up sooner and sound smoother, but can decrease tube life.
It really all depends on the tubes and the amp.
Personally I've found the Rebel 30 sounds best at the recommended voltage of 40mv.
You need a multimeter that can measure down to Milli-volts.
The amp has test points set up for easy access but be careful, you could get hurt or damage the amp if you touch anything besides the test points.

Check out this thread viewtopic.php?f=26&t=56736&p=782772&hilit=Rebel+30+Bias#p782772

It really is just related to tube life. Sounding better or worse at different voltages is up to the user's ears. Running tubes hotter could indeed decrease your tube life, and the recommended settings we supply are what we feel offers the best balance for tube life and tone. I'll be honest though, if you have never biased an amp, then I would consult someone who is comfortable to help you through it the first time. Biasing is easy, but touching the wrong thing in there could give you quite a nice shock.

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http://www.egnateramps.com