explanation cathode vs fixed

[tsutt]

Bias. Why one over the other advantages either way.

[Milkmansound]

http://www.aikenamps.com/Biasing.html

[tsutt]

Thanks but not what im after. my question is why do you build one way or other and for what reasons. is there characteristic of one that is better than the other? is there tonal consideration ect.

[xtian]

Cathode bias allows the current to fluctuate thru the cathode in response to signal amplitude, reducing power, and contributing to sag. See Fender Tweed.

Fixed bias does not allow this sag, and allows for greater power dissipation. See Marshall JCM 800 or the like.

I think Milkman meant to point to this page:

http://www.aikenamps.com/WhatIsBiasing.htm

[Phil_S]

In general, you'd probably use cathode bias in a lower power amp and almost always in a single ended amp. For a higher power push pull amp (more than maybe 30-35W) you will have a tough time getting the power with cathode bias. Your typical 50W and over amp will need fixed bias.

Also, there can be technical considerations. For example, the tremolo won't work on a Vibro Champ if you operate it in fixed bias because of the circuit design. You'd have to go for a different design to put tremolo into a SE amp.

We could always get into a discussion about class of operation (Class A vs. AB) but that tends to get muddy and contentious very quickly as people tend to be rather opinionated about it. I'd urge avoiding that whole area of discussion as it tends to be rather technical and difficult for an amateur to absorb.

[LeftyStrat]

There's also the issue of what happens when a power tube shorts. In cathode bias it will fry the cathode resistor, in fixed bias it can take out the OT.

[Reeltarded]

And that is why I started using solid copper staples instead of tubes.

No, I didn't.

[tsutt]

ok thats better. I'll leave it at that for now. i could ask constant questions. As because has never worked for me. So the next one would why wouldn't i be able to get power with a cathode bias, whats happening that it limits it. see where this could go. i'll let it sit. dont want to be a nuisance. This is how i learn best unfortunately. me and books are like oil and water. reference only. unless it a really good novel.

[Reeltarded]

Use Google buddy. Try searching with

site:ampgarage.com (search string)

Then be as Wordy McPosterson as you need to be.

[tsutt]

Just read the aiken page. will have to read it a few more times. The search function is way to broad dont like it at all.

[Reeltarded]

The internal one is but Google can almost read your mind.

[tsutt]

Thats because they have behavior analysis software attached to every move you make so they know what your going to do next. Big bro is looking out for you.

[Reeltarded]

I am big brother.

[Cygnus X1]

For a higher power push pull amp (more than maybe 30-35W) you will have a tough time getting the power with cathode bias. Your typical 50W and over amp will need fixed bias.

I have a Conn organ amp that I've been using as a stereo power amp for the garage.
It is (4) 6L6GC's running in two pairs, cathode biased.
(Yes I had to add another output transformer).

Never measured the power output on it but generally what should I expect?
70 watts?

[JoeCon]

Cygnus

2 6L6 at max dissapation would be 50 watts. Biased at 70% would be 35 watts a channel. So 70 watts stereo is a good guess.

How does it sound as a stero amp for palyback rather than organ?
I'd love a nice tube stereo amp, maybe another build for the list...

See ya!