Poweramp tubes recomendation/biasing

Jevil

Jevil

Pro Evolution Fucker
Apr 18, 2006
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I've got a Peavey Classic 50/50 Stereo Poweramp. The tubes were changed more than 9 years ago or perhaps never.
It is built with (8)EL84, (2)12AX7, (2)12AT7.

Any model/brand recommended?
It is for use with a Triaxis.

Another question, Peavey 50/50 is Fixed Bias, so i guess that I can change the tubes myself like if it were a preamp? No NASA engineering needed?
 
I have a peavey classic 60/60 and I've add a pot to set the bias level.
I've found a guide on the net to do that.
Try to search something similar for the 50/50

Good Luck
 
Yes the bias is important. Every set of tubes will have a different internal resistance which results in the amount of current drawn (and as a result output power). The output power dictates a large part of the sound. The idea behind biasing is that you are matching the same current from the previous tubes (which is set by the tone that you prefer)
 
matched just measn both tubes pull the same current to the same voltage, but does not mean the current will be correct at the amps rated voltage so that's where the biasing mod/trim contol comes into play, as it allows you to control that current to achieve the correct total output power. Which will affect tone and tube life, depending on which one you prefere over the other. Besides the 5150, peavey's generally come under biased and that makes a specific tone, if you are after that, but if you want a hotter sound, only a bias mid will do that. If you have a fixed bias your at the mercy of the output power dictated by the tubes, and each matched set will never have the same current/power, thats where biasing comes in, to fine tune so that each new set you put it sounds exactly like the previous ones.

However if you like the tone on your amp and really don't feel the need to bias its cool, but its a simple 10 dollar mod that takes 30 minutes to do or a few hours and about 70-80 if you have it done by a tech and like i said it helps tube consistency and the available amount of tube tone and total tube life. but still there is no wrong way of going about it, it is all preferance.
 
Yes it's important that the tubes are matched, otherwise you have to set the plate current for every tube, while if are matched all tube work at the same operating point.
But if the bias it's set low the tubes start to saturate later otherwise if bias it's set to loud the tubes start to saturate earlier.
If you are satisfied of the sound you can leave as is.
 
not only do the tubes saturate earlier at lower biasing, but they also sound thinner and more mid scooped, the higher bias sounds more thicker and sound darker, the mids will be more present.

again its still all preference, but its cool to know how the bias effects the tone.
 
again its still all preference, but its cool to know how the bias effects the tone.
Click to expand...

Yes in fact I've modded my peavey for this reason.
It also true that the various type of tube (6L6 or EL84) have their optimal level of current to work well.
 
I've read that Mesa and Peavey poweramps have fixed bias with low bias so they pass the 1st year of warranty.

So I've got 2 options, change the tubes myself without any mod and leave it low biased, or taking the poweramp to a tech to do the mod and tube changing 'cause I have no idea how to bias nor modding my poweramp (if you have a manual I would apreciate)

As far as i know high biasing may be harmful for the tubes and may not last for too long.
 
Mesa have the fixed bias beacause the rebranded mesa tubes have a specific number, when you have to replace tube you can buy the mesa tube with the same number and you don't need change the bias.
 
If you find the peavey selected tube, I think that you don't need to change bias, but the tone it's the same, but if you want to experiment with other types of tube and try different tone I suggest to add a pot for change the bias level.
 
Jevil said:
As far as i know high biasing may be harmful for the tubes and may not last for too long.
Click to expand...

biasing below the tubes rated power is not harmful, just shortens the tube life. Most people like the bias their tubes to 70% since there isn't much of a different in tone between 70 and 100%, just shorter tube life. Most Peavey's are biased at like 50 and the 5150 is around 10%.

The Bias low has nothing to do with warranty but it allows the tubes to last over the year so they don't have to give free tube replacements during that warranty. Its most brands cheep way from needing to do free normal wear and tear work that the owner should pay to have done in the first place. I don't think tubes should be warranted because they go out so easily and are not a part of the amp. High biasing will not hurt the amp's internals, just shorten tube life. However if you bias over 100% at high volumes you can burn the plate and that is known because the plate in the tube glow red. Once that happens, the tubes are fucked, but that won't happen unless so you bias well over 100%.

if you are really itching to have a different tone from your tubes have it sent to a tech to do it, if not, then keep it the way it is. Hotter tubes sound thicker, but not everyone likes that, you will have to judge if that tone is worth it
 
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