Cathode Bias and Fixed Bias

[ratherdashing]

Re: Cathode Bias and Fixed Bias

You don't have to run Mesa tubes in Mesa amps, only tubes that operate in the same range as Mesa tubes. I put JJs in my 2:90 and all I did was request tubes that were in the proper range for my amp.

Most tube marketing/selling businesses honor that request and it doesn't cost any extra.

Yup, exactly correct. Eurotubes, for instance, will sell you sets of tubes for Mesa amps that are within Mesa tolerances.

[bancika]

Re: Cathode Bias and Fixed Bias

this isn't going anywhere
Don't get me wrong, I love mesa amps and I'd like to own one (once I can afford it), but R.S is just not my favorite guy in amp making business.

To spice up the original theme of this post: another interesting bias method is with zener diodes, it sounds closer to fixed bias but cool thing about it is that you can mix it with regular cathode bias resistor to get anywhere between cathode bias compression and fixed bias tightness...
Another thing one can do is to bypass cathode bias resistor with a very large capacitor (like 2000uF), that should make the sound more tight and still not have to worry about biasing.

Cheers

[Pink Unicorn Horsey]

Re: Cathode Bias and Fixed Bias

So from a purely tonal standpoint, is one type of biasing generally considered more desirable than another?

- Keith

[bancika]

Re: Cathode Bias and Fixed Bias

really depends on the taste, if you need more compression and spongy feel you'll like cathode biased, if you like your tone to be precise and tight (like for palm muting) you'll want fixed bias.

[ratherdashing]

Re: Cathode Bias and Fixed Bias

this isn't going anywhere
Don't get me wrong, I love mesa amps and I'd like to own one (once I can afford it), but R.S is just not my favorite guy in amp making business.

Gee, really? I had no idea.

[Pink Unicorn Horsey]

Re: Cathode Bias and Fixed Bias

really depends on the taste, if you need more compression and spongy feel you'll like cathode biased, if you like your tone to be precise and tight (like for palm muting) you'll want fixed bias.

Good to know! I generally prefer the compressed and spongy vintage tones. Of course, I don't really do that with my Mesa, but I typically use that amp for modern stuff anyway.

- Keith

[jlm]

Re: Cathode Bias and Fixed Bias

"Since vacuum tubes are "normally on" devices, a trick can be used to bias them without having to supply a negative DC voltage source to the grid. If a resistor is placed between the cathode and ground, and the grid of the tube is referenced to ground (usually by connecting a large value resistor, such as a 1Meg, from grid to ground), the tube will try to conduct a large current from cathode to plate, since the grid and cathode are initially at ground potential. However, this cathode current flow will cause a voltage drop across the cathode resistor, making the cathode voltage positive with respect to the grid."

Not true. The reason cathode biasing works is because the cathode becomes somewhat positive in relation to the anode (plate). The grid then varies in potential regulating the flow of electrons from the cathode to the plate as is normal tube behavior.

[GoldenVulture]

Re: Cathode Bias and Fixed Bias

Er , you just posted to a thread that is 8 years dead.

[James Rock]

Re: Cathode Bias and Fixed Bias

Er , you just posted to a thread that is 8 years dead.

I didn't check the dates reading that and though I'd read it before.... And yup I read it 8 years ago...

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