Here's a stupid question (maybe) about fixed bias

[Russ]

No

 

[disassembled]

Some peavey amps are (classic series, 5150, ultra) i am sure there are MANY more i just have not poked around inside of them. Peavey does offer adjustable Bias in some of their amps (especially their newer ones).

Why do you want to know?

Greg

 

[t0aj15]

The Traynor YCV series are self biasing amps, which means all you have to do is insert the correct type power tubes (they don't even have to be a matched pair)and the bias is set automatically. Very handy feature when only one tube goes bad.

 

[jbird]

Personally, whether an amp needs biasing or not will/has not had any affect on my search for a specific tone. :?

 

[Guitarzan]

Personally, whether an amp needs biasing or not will/has not had any affect on my search for a specific tone. :?

Agreed.

If this is for home use why not get like a Cube 30 or a Zoom Fire 36. If it's just for practice I'd go that route.

 

[dumeril7]

Are Mesa's the only amps out there (new or used) that are fixed bias?

A technical point, but "fixed bias" means something a little different than the way you're using it.

Fixed biasing means the tube is biased by a DC voltage applied to the tube grid and can be varied by changing the bias voltage. In Mesa's case, the bias voltage is "hard-wired" so that you can't change it. However, garden variety Fenders and Marshalls are also "fixed bias", but you can vary the bias voltage by way of a trim pot inside the chassis. Both are considered "fixed bias", but the Fender and Marshall approach is adjustable and the Mesa is not. I suppose a better term would be "adjustable bias".

The alternative to fixed bias is cathode bias, which effectively self-adjusts the bias to the tubes.

D7

 

[TheRazMeister]

Crate V series 5/15/30 watts (not sure about the 50 watter)
B52-60 and 100 watters

Are Mesa's the only amps out there (new or used) that are fixed bias?

 

[Dutchman]

Fenders are kinda fixed bias.


I've been using one of these for a while now to check the bias of my tubes., works great. You do not want to leave it in the circuit very long but for setting/checking the bias is OK.

http://cgi.ebay.com/Dual-Bias-Tool-probe-for-tube-amplifier-amp-biasing_W0QQitemZ250099826905QQcategoryZ43375QQtcZphotoQQcmdZViewItem

 

[TheRazMeister]

Fenders are NOT "kinda" fixed bias. You can buy tubes in the same tolerance range but the bias will change even if you set it manually. My friend checks his Hot Rod Deluxe every few weeks and it fluctuates.

Fenders are kinda fixed bias.


I've been using one of these for a while now to check the bias of my tubes., works great. You do not want to leave it in the circuit very long but for setting/checking the bias is OK.

http://cgi.ebay.com/Dual-Bias-Tool-probe-for-tube-amplifier-amp-biasing_W0QQitemZ250099826905QQcategoryZ43375QQtcZphotoQQcmdZViewItem

 

[Dutchman]

The older Blackface and Silverfaced Fenders had one side fixed. No adjustment to that side. The thought at the time was you would adjust the Bias pot until you had minimal noise. The Bias pot would only be adjusting the voltage on one tube. There was no concern as to what voltage the tubes where actually operating at. Most of the time it was far from balanced.

So I should have stated one side was fixed instead of "Kinda"

I have not been inside a Hot Rod Deluxe, but I would imagine it has an adjustable bias.

All tube amps fluctuate somewhat. No matter what the Bias control technique or device is. It's the nature of the beast....

 

[TheRazMeister]

Interesting about the HRD is that the gain tone ( and tube lifespan) will change dramatically with a hotter bias setting. You lose headroom but get a more usable gain stage. I didn't realize that about the older Fenders, I stand corrected. 8)

I have not been inside a Hot Rod Deluxe, but I would imagine it has an adjustable bias.

All tube amps fluctuate somewhat. No matter what the Bias control technique or device is. It's the nature of the beast....

 

[dumeril7]

Fenders are NOT "kinda" fixed bias. You can buy tubes in the same tolerance range but the bias will change even if you set it manually. My friend checks his Hot Rod Deluxe every few weeks and it fluctuates.

Fenders are kinda fixed bias.


I've been using one of these for a while now to check the bias of my tubes., works great. You do not want to leave it in the circuit very long but for setting/checking the bias is OK.

http://cgi.ebay.com/Dual-Bias-Tool-probe-for-tube-amplifier-amp-biasing_W0QQitemZ250099826905QQcategoryZ43375QQtcZphotoQQcmdZViewItem

Not all Fenders are the same!!! Champs are cathode-biased (i.e. self-biasing). Many of the classic dual 6L6 models are adjustable, fixed bias. (Like I said in a previous post, an amp can be "fixed bias" and still be adjustable.) And some of the newer models are non-adjustable fixed bias. And some of the silverface and later blackface had a terrible (IMO) bias balance system that never really worked right.

I guess the reason I'm making a point about what fixed bias really means is because if you go to a tech, he will consider, say, a Marshall 2203 "fixed bias" even though it can be adjusted and you'll be speaking different languages....

D7