How is the correct tube "range" measured

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gronk62

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Ok so the internet is a great place for findin' out stuff.

BUT, there is also a HUGE amount of bullsh!t out there as well !

For non technical blokes like myself, its almost impossible to distinguish between fact and fiction sometimes. :roll:

I have owned a DC2 for about 6 years. Until recently I owned 2 of them but decided to let one go to help fund the purchase of one of these Aussie hand built beauties.. http://www.ledfordamps.com/pages/heads.htm

Anyway I'm gettin' sidetracked here.

It appears I've been lucky in the past when it came to buying off the shelf EL84's for my amp coz I've just plugged 'em in and it sounded sweet. No rebias. No "range" matching.

I know Mesa tubes fall into a certain "range" to suit the set bias but what I wanna know is how the "range" is measured?

For example. If I wanted to buy some EL 84's from one of the few local suppliers here in OZ I gotta order a "matched" pair.
This is the easy part.
The not so easy part is getting a matched pair that fall into the correct and suitable "range" for a Mesa EL 84 powered amp.

Is this mystical "range" something that can be measured with a multimeter?

Is there anybody here who can give me the correct information ?
 
You would have to measure the bias current in the amp you are using.Back in 1981 before I learned to do it myself and put an adjustable pot in the bias supply,the tech I used to use would try a few different matched pairs till we found the right ones.He was the tech in a studio I worked in at the time so he wouldnt charge me for this service.Mesa buys big lots and measure the current and group them in a certain range.
 
Ok so they need to be installed in an amp (or machine) to be measured.

So if the local aussie tube suppliers don't have a machine to install them in for measurement then there is no way they can supply me with tubes that will fall within the safe working range on my amp....unless by luck.

Looks like I better stick to the previous plan of buying them from Eurotubes or similar place.

Thanks Stokes.
 
I think it would be better if they put them in your amp and measure the bias to see if they "fit".You would need to take it to a tech,unless your tube supplier has a meter and is willing to try a couple of sets to find the right set.Putting them in a "machine" isnt going to tell what they will do in your particular amp.Mesa can do that to a certain degree because they biased your amp when they built it.If it is that hard to find a tech or such,maybe you should invest a little time and learn to do it yourself,you may find it interesting.....and maybe not.Lots of guitarists do it themselves.Or just order from Mesa or if Euro can fit you probably better,I read a lot of good things about them.
 
stokes said:
I think it would be better if they put them in your amp and measure the bias to see if they "fit".You would need to take it to a tech,unless your tube supplier has a meter and is willing to try a couple of sets to find the right set..
Click to expand...
Unfortunately goin' to a tech is not an economically viable option for me as the closest tech I know of is about an hour and a half away. 3 hours round trip to drop the amp off and another 3 hours to pick it up when its done.

Even bigger problem with the closest tube supplier who is over 4 hours away.
 
If you can order from Sears they have a Fluke 81438 Multi for about $100.If youcan find it get G.Webers latest book"Tube Guitar Amplifier Essentials".Lot of good info there.I'm sure there are many out there who will suggest other books,they are all good.Get them all if you can.It aint that hard to bias an amp,once you start doing it yourself you will be much more satisfied with your amp.Plenty of info right here on this forum,just ask and you'll get lots of answers,as you see already.Another good forum is AMPAGE.It looks like your best option is to DIY.
 
Thanks for all the advice.

I was hoping there was a simple way to test tubes but looks like thats not the case.

I definately won't be attempting any probing around inside my amp. I have zero electronics ability.

I'll stick with the plug and play method.

cheers
cheers.gif
 
We all had zero electronics ability before we learned.With the internet its even easier to learn these days,so much info on the topic these days.
 

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