I'm trying to investigate a BUNCH of vacuum tubes I have, and as I do, I grab the datasheets before I do anything. I have no idea what to expect as of yet as I check on them. What is the mininum ballpark plate to cathode voltage for most tubes to work?

I'm trying to check them out at a low voltage before I throw 140VDC (partly to save me some unnecessary pain from getting shocked). Is it often the abstract "Value 1 and Value 2 range I'm seeing on the datasheets? (For example, a 6V6-GT/G tube shows 90 volts and 240 volts. Does this mean I need 90 volts to make the tube do anything?)

What's some other things I need to know that I can't decipher from the datasheets?

 

Hello,

There are tubes that even work at 12 Volts:
http://www.sophtamps.ca/schematics/sopht_12k5-v6.jpg

Bertus

 

I haven't seen any 12V7 tubes in my stash yet, but I'll look for them.

 

Hello,

There are some old books for download at the Pmillet ste:
http://www.tubebooks.org/technical_books_online.htm

There you will also find a section about tubes.

Bertus

 

Hi;

I'm trying to investigate a BUNCH of vacuum tubes I have, and as I do, I grab the datasheets before I do anything. I have no idea what to expect as of yet as I check on them. What is the mininum ballpark plate to cathode voltage for most tubes to work?

I'm trying to check them out at a low voltage before I throw 140VDC (partly to save me some unnecessary pain from getting shocked). Is it often the abstract "Value 1 and Value 2 range I'm seeing on the datasheets? (For example, a 6V6-GT/G tube shows 90 volts and 240 volts. Does this mean I need 90 volts to make the tube do anything?)

What's some other things I need to know that I can't decipher from the datasheets?

See if you can find an old RCA tube manual possibly on line or in the library. The tube manual has the characteristics of many tubes along with other information on circuitry and test procedures.

 

There are plenty of tube datasheets on the internet. Franks is one. Here's another:
http://tubedata.milbert.com/sheets65.html

They show the maximums but you don't have to run a vacuum tube at its maximum voltage, current, or power. I've seen a 12AX7 run at 12 volts and I've designed them to run on 70 volts. My customers love my products because I don't obey the rules and I get excellent results.

 

In order to test a tube you should test it at the voltages for which it was designed. For example when testing cathode emission (frequent wear-out phenomenon) all of the electrodes need to be at the correct voltage. If you just want to check for shorts between elements (rare) and open heaters (no terribly rare) that is a simpler matter.


There are tube handbooks on the Internet Archive that you might find useful.
Internet Archive of Tube Handbooks <= this opens a web page

You can find examples of tube testers on the internet. A link to one of them is below.
An inexpensive, easy to build diy valve/tube tester - Valve Heaven <= link to pdf file

 

My intent is to build an "experimental circuit" to see how changing certain values will affect the tube. Since I will be exposed to the circuit during testing, that explains why I wanted to keep the voltages down.

Although this question is unrelated, I see some of my tubes have a black coating inside them which looks like paint, which is separate from the typical silvering of the getter material, and others of the same type do not. My 6SN7 in particular are this way. What is this coating for and what makes this tube different than the uncoated ones? Is it that the coating is designed to trap heat and allow the tube to run at a higher emissivity?

 

Hello,

Perhaps the following page will tell you more about the 6SN7:
http://www.effectrode.com/signal-tubes/the-6sn7gt-the-best-general-purpose-dual-triode/

Bertus