#1
Hi all! I'm very new to tube amplifiers. I haven't bought one yet, but I've been reading about them a lot. I've been wanting a tube amplifier and I've been looking into this one and playing it a bit at Guitar Center.

http://guitars.musiciansfriend.com/product/Peavey-6505-112-60W-1x12-Tube-Combo-Guitar-Amp?sku=582106

One thing I'm not sure about is replacing the tubes themselves and adjusting the bias on the tubes. I've read that the Peavey amp's tubes run "cold" but I'm not sure if or how the bias can be adjusted on these amps. I'm sure it's not hard to replace the tubes, but adjusting anything else seems like something I wouldn't really want to do.
I was wondering if adjusting the bias is ABSOLUTELY necessary. Since the amp already uses 12AX7's and 6L6GC's, when the time comes to replace them, could I just put in new tubes of that those types without adjusting anything? I was looking at the Electro-Harmonix 12AX7EH's and the 6L6EH's.
Any useful tips or advice?
#2
You won't have to worry about changing the tubes for a very long time. 2 years minimum under normal use. Longer for the preamp tubes. You don't have to bias unless the power tubes are redplating. I'm not sure if there's even a bias trimmer in the Peavey though.
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#3
Biasing just seems to best way to get the most out of your amp, However you may like the tone of a colder bias, or a hotter bias, but it does have a affect on the time the tubes will last
#4
A good reading on the bias test points is - 46 volts. As you reduce the grid voltage, the tubes will run hotter, so for tone purposes I don't adjust it to anything more positive than - 43 because the tone starts to mush out, and that's not a very desirable thing with the 6505's.

All that being said, I wouldn't worry about damaging the tubes in a stock 6505, even the new ones. Peavey has seen to it to install a limiting resistor across the bias trim pot that keeps one from lowering the grid voltage too much and burning up the power tubes.
Tastes like chicken, if chicken was a candy.
#5
The bias on a 6505 is not adjustable (unless you mod it), so don't worry about that.

So you'd just put new ones in and that's it.


EDIT: ^Huh? I thought they didn't even have a trimpot?
Last edited by TheQuailman at Aug 26, 2010,
#6
Quote by TheQuailman
The bias on a 6505 is not adjustable (unless you mod it), so don't worry about that.

So you'd just put new ones in and that's it.


EDIT: ^Huh? I thought they didn't even have a trimpot?


Sorry, should have been specific. the 6505+ is the only of the two models that has a bias trim pot. I was referring to those, since the OP posted a link to the +.
Tastes like chicken, if chicken was a candy.
Last edited by ConfederateAxe at Aug 26, 2010,
#8
So basically, if i'm content with the tone, I don't have have to worry about adjusting the bias of the tubes?
#9
Quote by IbanezAsbo
So basically, if i'm content with the tone, I don't have have to worry about adjusting the bias of the tubes?



Exactly.
Tastes like chicken, if chicken was a candy.
#11
For trivia, if an amp has that it is 'Fixed biased' or 'Cathode biased' (Same thing), means that you simply order a matched set of Power Tubes, and your golden.
There will be no need to have the amp re-biased.
#12
Quote by BurstBucker Pro
For trivia, if an amp has that it is 'Fixed biased' or 'Cathode biased' (Same thing), means that you simply order a matched set of Power Tubes, and your golden.
There will be no need to have the amp re-biased.


Cathode bias and fixed bias are definitely not the same thing. I suggest a bit of reading on the technical aspects of amps before making that claim.
E-peen:
Rhodes Gemini
Fryette Ultra Lead
Peavey 6505
THD Flexi 50

Gibson R0 Prototype
EBMM JP13 Rosewood
Fender CS Mary Kaye

WTLT

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#13
Quote by mmolteratx
Cathode bias and fixed bias are definitely not the same thing. I suggest a bit of reading on the technical aspects of amps before making that claim.


Good call...
http://thetubestore.com/powertubeinfo.html

"Fixed bias amplifiers CAN'T be bias adjusted".

"Cathode bias amplifiers shouldn't require any adjustments and will work with a wide range of tube plate currents, as the circuit is "self adjusting".


"There will be no need to have the amp re-biased". Still true.
#14
lol

Even the Tube Store doesn't know what they're talking about. Fixed bias doesn't refer to the adjustability of bias. It refers to a negative voltage applied to the grid with respect to the cathode. There's adjustable fixed bias and there's non adjustable fixed bias. You can convert a non adjustable to adjustable by simply clipping the bias resistor and wiring in a pot as a variable resistor in its place.
E-peen:
Rhodes Gemini
Fryette Ultra Lead
Peavey 6505
THD Flexi 50

Gibson R0 Prototype
EBMM JP13 Rosewood
Fender CS Mary Kaye

WTLT

(512) Audio Engineering - Custom Pedal Builds, Mods and Repairs
#15
Quote by BurstBucker Pro
Good call...
http://thetubestore.com/powertubeinfo.html

"Fixed bias amplifiers CAN'T be bias adjusted".

"Cathode bias amplifiers shouldn't require any adjustments and will work with a wide range of tube plate currents, as the circuit is "self adjusting".


"There will be no need to have the amp re-biased". Still true.



^I don't think that is accurate either

Fixed bias amps CAN be biased. I just did mine. Fixed bias means YOU FIX the amp bias to what sounds best and what is recommended by the manufacturer.

Non-adjustable Fixed though would fit that description of 'CAN'T be bias adjusted' unless it is modded as Matt said.
Last edited by 311ZOSOVHJH at Aug 27, 2010,