Trace, can you explain the Bias #s and the tube relationship

[Laars]

Hi Trace,
I've been using only Groove tubes since the early 80s and I'm trying to understand the numbers written on the tubes and how it relates to the amps bias you put on the back of my amps.

My Voodoo V-plex's have stickers on the back from when you biased the amps. Its got the date, and then it says "amps bias : 30 Ma" . They are Svetlana EL34s.

My question is, I need to bring spare tubes with me, so I'd like to get tubes as close as possible. I've seen where tubes other then groove tubes have these numbers on them.

B+ voltage is 400 V DC
Plate current is 29.5 (almost 30)
GM 5100

What do these numbers on the tubes tell me, and how does it help me pick out tubes for my amps that will work?

Does the bias number on my amp (30 Ma) mean the same as the plate current I see on the tubes? Can I just get backup tubes like the ones shown above?

Is the B+ voltage in the Vplex's set to a certain number and if so what is it.

I guess I'm asking how can I get a backup set of tubes for my V-plex that has Svetlana El34s in them, that you biased the amp to 30 mA.

What other numbers on the tubes do I need to match?

I'm really starting to think that just putting Groove tubes in the amp sure does make all this easier.

 

[voodooamps]

Hi Trace,
I've been using only Groove tubes since the early 80s and I'm trying to understand the numbers written on the tubes and how it relates to the amps bias you put on the back of my amps. My Voodoo V-plex's have stickers on the back from when you biased the amps. Its got the date, and then it says "amps bias : 30 Ma" . They are Svetlana EL34s.

We do not place stickers with bias readings on amps, I presume that these stickers were put on by a prior owner.

My question is, I need to bring spare tubes with me, so I'd like to get tubes as close as possible. I've seen where tubes other then groove tubes have these numbers on them.

B+ voltage is 400 V DC
Plate current is 29.5 (almost 30)
GM 5100

I am honestly not certain how one tube company's readings translate to another tube companies readings, as readings vary when using various different testers. What I can tell you is that we burn in all of our tubes for 72 hours, then test/select and match tubes at real world voltages. IE: When tube companies match tubes at 400VDC they are not matched when you put them in an amp that runs 450V or higher. 450V to 475V are normal operating voltages on the majority of most modern production tube amplifiers.

In short; I would recommend purchasing a Bias Meter/Tool such as a Weber Bias Rite, Allesandro Bias Meter, etc. They come with basic instructions that will get you up and running.

What do these numbers on the tubes tell me, and how does it help me pick out tubes for my amps that will work? Does the bias number on my amp (30 Ma) mean the same as the plate current I see on the tubes? Can I just get backup tubes like the ones shown above?

There is a great deal of info on the net regarding this. If you like give the shop a call this week and have something you can take notes with (computer, pen/paper, etc). I can give you the basic info you will need to know.

Is the B+ voltage in the Vplex's set to a certain number and if so what is it.

A tube amplifiers B+ plate voltage does not remain at a fixed number. IE: when you alter/change the bias the B+ voltage changes in turn. When in install a set of power tubes that draws more/less current the B+ voltage changes.

 

[Laars]

Hi Trace,
Thanks for the response. I guess this is the reason I don't use other tubes, and I've stuck to just using Groove Tubes. I put tubes in, have it biased, and then keep the same GT numbers and don't have to worry about it.

 

[voodooamps]

Feel free to call me, I think you may enjoy the tones more if you try some different power tubes.

607-256-0465
Trace