What a difference a few mVDC on bias can make

[NoOnesFang13]

I had my Egnater Tweaker 40 1x12 serviced a couple months ago and they replaced the power tubes and rebaised it, according to the receipt I got. Since then every time I plug in I just didn't feel connected with it. The low end seems less controlled, and the highs seems to be harder and more brittle. I didn't know what kind of tubes they put in, so I decided to take a look and see what I could do. It was a bit of a PITA to get to everything but I checked the tubes and they were Electro-Harmonix 6L6EH, so I went ahead and checked the bias it was sitting at around 72 mVDC. According to what ive read about the 6L6 this is pretty normal, but on the board of the amp it says to set it to 65mVDC which seems to be on the cold side from what ive read. But I figured I would set it as close as I could. So I got it to 64mVDC and tried it out. But the low end seemed more controlled and overall the amp seemed to open up a lot more. I have no idea how much of that is psychosomatic but now when I play I actually feel inspired, instead of constantly messing with stuff trying to get a good base tone.

 

[Jacew]

Re: What a difference a few mVDC on bias can make

I had my Egnater Tweaker 40 1x12 serviced a couple months ago and they replaced the power tubes and rebaised it, according to the receipt I got. Since then every time I plug in I just didn't feel connected with it. The low end seems less controlled, and the highs seems to be harder and more brittle. I didn't know what kind of tubes they put in, so I decided to take a look and see what I could do. It was a bit of a PITA to get to everything but I checked the tubes and they were Electro-Harmonix 6L6EH, so I went ahead and checked the bias it was sitting at around 72 mVDC. According to what ive read about the 6L6 this is pretty normal, but on the board of the amp it says to set it to 65mVDC which seems to be on the cold side from what ive read. But I figured I would set it as close as I could. So I got it to 64mVDC and tried it out. But the low end seemed more controlled and overall the amp seemed to open up a lot more. I have no idea how much of that is psychosomatic but now when I play I actually feel inspired, instead of constantly messing with stuff trying to get a good base tone.

I noticed the same tweaking the cathode bias resistor values in Orange TT couple of years back. Didn't measure the mA, but was really surprised how sensitive it was even to slight changes.

https://forum.seymourduncan.com/showthread.php?317737-Tiny-Terror-bias&hig

 

[Gtrjunior]

What a difference a few mVDC on bias can make

I too have noticed this with my Quickrod. It absolutely prefers to be biased a little cold.
Biased too hot and there just a strange “something” in the upper mids...a harshness or something.
Biased colder and the amp just RIPS.

 

[NoOnesFang13]

Re: What a difference a few mVDC on bias can make

I too have noticed this with my Quickrod. I absolutely prefers to be biased a little cold.
Biased too hot and there just a strange “something” in the upper mids...a harshness or something.
Biased colder and the amp just RIPS.

I think that's how I felt with my amp. Upper mids more than highs were harsh maybe. All I know is it sounds so much better now

 

[Gtrjunior]

Re: What a difference a few mVDC on bias can make

I think that's how I felt with my amp. Upper mids more than highs were harsh maybe. All I know is it sounds so much better now

Yeah, almost a grainy quality. It’s tough to describe.

 

[dystrust]

Re: What a difference a few mVDC on bias can make

It really depends on the amp.

The only one of mine where I've tinkered with bias a lot is the Jubilee 2555, because at the time I was too broke to have a tech do it. I found that I liked it best at roughly 36ma per EL-34; if it was set colder than 34 it would get brittle bright and lose a lot of low end. If it was set higher than 37, it'd be bassy and and extremely loud while losing a bunch of headroom.

 

[Gtrjunior]

Re: What a difference a few mVDC on bias can make

It really depends on the amp.

The only one of mine where I've tinkered with bias a lot is the Jubilee 2555, because at the time I was too broke to have a tech do it. I found that I liked it best at roughly 36ma per EL-34; if it was set colder than 34 it would get brittle bright and lose a lot of low end. If it was set higher than 37, it'd be bassy and and extremely loud while losing a bunch of headroom.

My JCM800 also likes to be biased slightly hot.

 

[Lake Placid Blues]

Re: What a difference a few mVDC on bias can make

That is one of the advantages of fixed (adjustable) bias. You can fine tune the amp to your liking.

 

[ehdwuld]

Re: What a difference a few mVDC on bias can make

My Belair came biased at 70
I tweaked it hotter to 78

It has a growl now

Much more personality

 

[dystrust]

Re: What a difference a few mVDC on bias can make

That is one of the advantages of fixed (adjustable) bias. You can fine tune the amp to your liking.

I'm not sure where the cathode bias on the Mini Jube is set, but thankfully it sounds great with the right tubes (did not like the factory Tung-Sols). I haven't tried a ton of different options, but I'm really digging JJ EL-34s which happen to also sound great in my 2555.

 

[Lake Placid Blues]

Re: What a difference a few mVDC on bias can make

I'm not sure where the cathode bias on the Mini Jube is set, but thankfully it sounds great with the right tubes (did not like the factory Tung-Sols). I haven't tried a ton of different options, but I'm really digging JJ EL-34s which happen to also sound great in my 2555.

I didn't like the Tung Sols in the mini either. They sound good in my 50 watt biased at around 68%, though. Right now I'm using EH 6CA7s in the mini. I have also used KT66s in it and they sounded great for more bluesy sounds. The cathode bias on the mini seems to work good with a diverse range of tube types.

 

[misterwhizzy]

Re: What a difference a few mVDC on bias can make

Just bought a pair of those EH 6CA7’s with Tube Depot’s recent sale. But I’ve been modding/repairing the amp so much recently that I don’t want to do any more tweaking for the near future, and the JJ’s it has now are fine. Do I have to surrender my forum membership now?