#1
Hi.

1. What does it mean to "bias" an amplifier?

2. What are symptoms of busted tubes (preamp or poweramp tubes)?

3. What can possibly go wrong if impedance is not set right?


Thanks in advance.
Har nånn egentli vorri langt sjøl om bestemt sæ for å bruk t å me gå å vill å gjør sjå mer lik?
#2
1. What does it mean to "bias" an amplifier?
Optimizing the plate dissipation for tube life and tone.
2. What are symptoms of busted tubes (preamp or poweramp tubes)?
Extra noise, less volume than usual, no sound at all.
3. What can possibly go wrong if impedance is not set right?
You can blow up your output transformer and/or your power tubes.
#3
Bump as americans start to wake up.
Har nånn egentli vorri langt sjøl om bestemt sæ for å bruk t å me gå å vill å gjør sjå mer lik?
#4
Quote by perkristian876
Bump as americans start to wake up.

Why? Colin answered everything. If you want to read it twice, check out the stickeyed tube thread.
#5
Quote by perkristian876
Bump as americans start to wake up.

lulz, at 3pm here. I got up 9 hours ago, went to work, came back, and answered your question. You should bump for the australian crowd though.
#6
Quote by the.spine.surfs
Why? Colin answered everything. If you want to read it twice, check out the stickeyed tube thread.



Yeah, okay... I guess he did.

But need a more detailet answer on the Bias question.


EDIT: Heard biasing is something you should do if you switch out all you're tubes to make the voltage right or something.

EDIT: roc, thanks for the answer. I am not ungrateful
Har nånn egentli vorri langt sjøl om bestemt sæ for å bruk t å me gå å vill å gjør sjå mer lik?
#7
Quote by perkristian876
Yeah, okay... I guess he did.

But need a more detailet answer on the Bias question.

Ask and ye shall receive.
Biasing means that you're changing the negative grid voltage of your tubes so that they run at the proper current. A dumb analogy is: You want to paint the top story of your house, but you're too short. So you get a ladder. The ladder in this case is the bias- it allows you to work at the proper level. If you need to paint the bottom story, you get off the ladder.

Technical guru and ampmaker Randall Aiken on the subject:
http://www.aikenamps.com/WhatIsBiasing.htm

EDIT: Heard biasing is something you should do if you switch out all you're tubes to make the voltage right or something.
Yes, that's correct. You need to set the bias every time you change power tubes because the tubes themselves are not exactly the same electrically (even the same tube from the same company), and the bias helps them run exactly as they were designed to.
#8
Quote by Roc8995
Ask and ye shall receive.
Biasing means that you're changing the negative grid voltage of your tubes so that they run at the proper current. A dumb analogy is: You want to paint the top story of your house, but you're too short. So you get a ladder. The ladder in this case is the bias- it allows you to work at the proper level. If you need to paint the bottom story, you get off the ladder.

Technical guru and ampmaker Randall Aiken on the subject:
http://www.aikenamps.com/WhatIsBiasing.htm

EDIT: Heard biasing is something you should do if you switch out all you're tubes to make the voltage right or something.
Yes, that's correct. You need to set the bias every time you change power tubes because the tubes themselves are not exactly the same electrically (even the same tube from the same company), and the bias helps them run exactly as they were designed to.


Thanks Great one


But is Bias a thing? You mention the bias :p How do you Bias an amplifier?

EDIT: I am built this way: If i don't know how something work or why a algebra piece is correct, i freak out!
Har nånn egentli vorri langt sjøl om bestemt sæ for å bruk t å me gå å vill å gjør sjå mer lik?
Last edited by perkristian876 at Apr 7, 2008,
#9
Quote by Roc8995
Yes, that's correct. You need to set the bias every time you change power tubes because the tubes themselves are not exactly the same electrically (even the same tube from the same company), and the bias helps them run exactly as they were designed to.



Sorry for hijacking, but do you still have to get your amp biased even if your amp is cathode bias?
#11
Quote by esp1234
Sorry for hijacking, but do you still have to get your amp biased even if your amp is cathode bias?

Not generally. You won't have to bias from one 6L6 to another, but you might have to bias if you try to jam some EL34's in there. Mabye not. My Champ 600 was cathode biased, and ran with both a 6V6 and 6L6.
#12
^
Ah well, I'm just going to use El84's and and 12ax7's like the amp originally had, just different brands (JJ)
#13
Quote by esp1234
^
Ah well, I'm just going to use El84's and and 12ax7's like the amp originally had, just different brands (JJ)

You're good. Just makes sure the 84's are matched.
#14
Quote by the.spine.surfs
You're good. Just makes sure the 84's are matched.


Damn, I seem to be hanging on you for advice of late . Do you know if the ValveKing is cathode bias?

P.S - You are godly.

P.P.S - Feel free to sig lol.
...
#16
Fixed it is. Rather annoying. You should be fine with any matched pair of 84's anyway.

No thanks, I prefer to sig people who hate me.
#17
Quote by esp1234
^
Valveking is fixed bias.


Bastards. Why can't every amp be cathode bias?! It would simplify things a LOT.
...
#18
Quote by bartdevil_metal
Bastards. Why can't every amp be cathode bias?! It would simplify things a LOT.

It's not terribbly efficient, or toneful or something. Colin would know.
#19
Quote by the.spine.surfs
It's not terribbly efficient, or toneful or something. Colin would know.

It's very toneful! A lot of the traits people mistake for "Class A" characteristics are actually due to the cathode bias (The AC30 is of course the classic example). It's a very open, vocal overdrive. The touch-sensitivity is due to extra clean sustain which blurs the transition from clean to OD- an interesting phenomenon that some amp makers exploit very well. Think of Brian May- he's got an AC30 (bright amp) turned all the way up with a treble booster, and it sounds very cool, swirly, thick, whatever you want to call it. The same setup with a Marshall- think Ritchie Blackmore- is a much "harder," colder OD- very good for early metal.

aaanyway, Cathode bias isn't used in a lot of amps because:
You lose some power
It has a more "vintage" OD that doesn't suit more modern styles
It's harder to change tube types
etc etc.
You can bias a cathode bias amp, but it's not usually necessary unless you're changing the rectifier tube type or the amp is rather old.