A Couple Of Questions About Tubes

[unclej]

(1) what tests, if any, can be performed on a tube with just a pin out and an ohm meter?

(2) how do you tell, other than experience, how to effect changes in an amp's performance by changing tubes? for example, if you wanted to increase or decrease gain how would you know which replacement tube to use? is there a big chart somewhere that gives the performance numbers on different tubes?

[Reaper]

I have seen (couldn't tell ya where), charts of what tubes have certain general characteristics. I think it's Groove Tubes that actually numbers theirs 1-10 on a basis of "hardness", and how they distort. You might drop them an email, they'd be able to tell you.

[unclej]

thanks reaper, i'm about to order some things from them and i'll ask then.

[Drak]

Go HERE, once you get there, click on the blue 'bulletin boards' button, once there, then look over on the left, and click on 'tubes'.

That will take you to Weber's tubes forum, a great place and very knowledgable people there. Also look up at the top of the tubes page, I think theres a lot of reference information there, probably including the charts you were looking for.

Also, find KCA Tubes. Mike Kropotkin. SUPER nice and informative guy.

You want to see REAL tubes for sale, go to Mike's site. Ultra-Complete site with descriptions and user comments and everything.

Groove Tubes, what they do is buy Chinese, Russian, and Czechoslovakian made tubes, rate them, number them, and rebrand them with the Groove Tube logo.

This is an old practice and is called relabelling in the tube world.

I am a complete tube snob, hehehe. All my tubes are old USA or English made from the 40's, 50's and 60's, I have a huge box of tubes I bought several years ago over a stretch of time, I think I'm set for life.

E-Bay is a good place to buy pre-amp tubes if you know what your looking at.

I usually buy my matched power tubes from Mike or other vendors who advertise on Weber's Buy-N-Sell 'board, almost everyone who posts there is credible and trustworthy.

[Paul Marossy]

if you wanted to increase or decrease gain how would you know which replacement tube to use? is there a big chart somewhere that gives the performance numbers on different tubes?

With preamp tubes, this is "easily" done. Check out this page for a general guideline: http://www.thetubestore.com/gainfactor.html

You have to take this chart with a grain of salt, as different tubes have different max. operating voltages, etc.

Substituting power tubes is not so easy. It involves changing the bias, there are different amounts of heater currents required for the various power tubes (power transformer may not have enough heater current for some power tubes), pinouts are not the same between all power tubes, etc., etc.

[unclej]

gentlemen..i sure hope everyone appreciates you guys as much as i do. it amazes me sometimes the incredible amount of knowledge represented by this site and how willing you all are to share.

drak, that's a great site! i didn't spend a lot of time there this morning but they even have a bias calculator on the tube page. how cool is that?

paul, that's exactly the info that i was looking for. thanks as usual.

hopefully one day i'll have learned enough to be able to contribute a little myself.

thanks again

[Paul Marossy]

Glad to be of service.