Jump to content
aberdeen-music
Sign in to follow this  
fatboy

tube grade

Recommended Posts

needing some advice peeps

got a set of valves for my birthday from my dad, he ordered them online so didn't choose them myself

i think they're these ones but could be mistaken 6L6SVT WINGED 'C'

have a look at actual pictures to be sure?(

154688_459980189479_564969479_5467165_5585352_n.jpg

77123_459981429479_564969479_5467205_1399838_n.jpg

as you can see they base of the valves has "pc 70" and "tc 6" on them and on the box, they are quad matched and each box has an orange sticker

now according to the bugera biasing instructions (see below) the voltage bias needs be set to the grade of tubes that is installed

149256_461438674479_564969479_5484600_7896618_n.jpg

what are the grade of tubes i have bought so i can properly bias my amp

does the "winged C's" mean that the grade of the tube is C???

please help thankenyoumuchly :)

Share this post


Link to post
Share on other sites

You can bias your amp as you please. It doesn't have to be exactly as they say. My Peavey is biased a lot colder than the tubes should be biased at. The ones in my Marshall are probably the same.

Nice choice of tube, I put them in my Marshall. Best thing I did :)

Share this post


Link to post
Share on other sites

Can you explain what biasing actually means at what benefits you get if you bias it colder, warmer, if you can or cant do this on some amps? I have a H&K switchblade which just self-biases apparently, having not ahd to change the valves myself yet i've not had to do it but as far as i know you just pop them in and out on mine and your good to go. But i'm still interested to know what biasing actually means and different stuff you can do.

Share this post


Link to post
Share on other sites

Biasing basically means altering the voltage across the valves in your amp. Each amp will have a specific biasing range, e.g. my 50W Vintage Modern likes its valves between 44 to 48 mV.

Biasing an amp "hot" means increasing the voltage above the recommended range. I think this means that the sound will break up (distort) quicker but the side effect of this is your valves will also die quicker.

Biasing the amp "cold" means decreasing the voltage below the recommended range. As the inverse of hot, this will smooth out your sound and make valves last longer.

Perhaps obviously, too hot or too cold will make your amp sound like arse... Although, some [strange] people quite like this!

I believe the grading above describes the break up of the tube. I can't remember whether A grade break up first or last but I'm pretty sure that's what the spectrum illustrates.

Share this post


Link to post
Share on other sites

Biasing your amp cold will make your output tubes last longer. This isn't a bad thing, especially if you're running your amp very loud a lot of the time. If you bias your tubes hotter and use the amp loud a lot, the life of your tubes will decrease quicker. If you bias your amp hotter, you'll also get saturation earlier than if you bias them cold.

Pretty much every amp company put their amps out biased very cold, mainly to make the tubes last longer. With your Bugera, I wouldn't worry about it being biased hot. It'll work quite well biased on the cold side.

Share this post


Link to post
Share on other sites
Biasing an amp "hot" means increasing the voltage above the recommended range. I think this means that the sound will break up (distort) quicker but the side effect of this is your valves will also die quicker.

Biasing the amp "cold" means decreasing the voltage below the recommended range. As the inverse of hot, this will smooth out your sound and make valves last longer.

I think that might be the wrong way round in part. My understanding is that higher voltage means they can run with greater volume and clarity before breaking up and lower voltage means they break up sooner.

"Apart from this safety/valve survival issue, bias adjustment becomes a matter of taste. High current gives you power/volume, clarity, good top end. If the idle current is set too high (under bias) then the valves will run too hot and the life of the valves will be reduced significantly. Less current gives you earlier break-up, with less volume, less clarity and top end. If the current is set too low (over bias) the tone of the amp may be thin and lacking volume."

How to bias a valve amplifier, valve amplifier biasing, biasing valves, from hifiandaudio.com, Review Hifiandaudio.com, about hifiandaudio.com

"Don't be confused with terms like "raising the bias". This is a bit confusing because raising the bias voltage, I.E. making the bias voltage bigger by going from -40vdc to -50vdc will cause the tube dissipation to be reduced. Or it could mean to make the bias voltage more positive by going from -50vdc to -40vdc causing the tube to dissipate more power."

Types of Tube - Valve Bias Information HTML Page

Share this post


Link to post
Share on other sites
I think that might be the wrong way round in part. My understanding is that higher voltage means they can run with greater volume and clarity before breaking up and lower voltage means they break up sooner.

"Apart from this safety/valve survival issue, bias adjustment becomes a matter of taste. High current gives you power/volume, clarity, good top end. If the idle current is set too high (under bias) then the valves will run too hot and the life of the valves will be reduced significantly. Less current gives you earlier break-up, with less volume, less clarity and top end. If the current is set too low (over bias) the tone of the amp may be thin and lacking volume."

How to bias a valve amplifier, valve amplifier biasing, biasing valves, from hifiandaudio.com, Review Hifiandaudio.com, about hifiandaudio.com

"Don't be confused with terms like "raising the bias". This is a bit confusing because raising the bias voltage, I.E. making the bias voltage bigger by going from -40vdc to -50vdc will cause the tube dissipation to be reduced. Or it could mean to make the bias voltage more positive by going from -50vdc to -40vdc causing the tube to dissipate more power."

Types of Tube - Valve Bias Information HTML Page

I think you're confusing voltage and current.

Your first example mentions "high current" which implicitly means "low voltage" (P = IV), i.e. cold biased or reducing the voltage across the valves.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

Sign in to follow this  

×