Tube Pins Explained Please

[Songman68]

Hi guys, I have built three amps from kits and I am really good at putting them together if I have a layout diagram. I have actually become very good at building amps. But my knowledge is lacking on the pins of a preamp tube.
I guess you could say with building amps I am like a guitar player that can play really well without being able to read a lick of music. I can build an amp and build it well, but I have no clue when it comes to reading a schematic or which pin is which on a preamp tube or power tube as to Plate, Grid, Cathode, Screen Grid. If I have a layout diagram though I can solder the crap out of an amp and get that thing fired up the first try.

Could someone please explain the following to me?

I know that a preamp tube has two sides consisting of the Plate, Grid, and Cathode I think.

So which pin # is the plate
Which Pin # is the Grid
Which Pin # is the Cathode
For each half of the triode please?

Could you please do the same for a Pentode as well for each pin?
I have done some searches on the web for this stuff, but none of the stuff I have found breaks it down to the pin. Like pin 1 is grid, pin 2 is Cathode or plate or whatever.

I will appreciate any help that I can get for this.

[57chevy]

Not all tubes have the same pin assignments. Use this link to find the info you want for a particular tube.

http://tdsl.duncanamps.com/tubesearch.php

[RobPlatt]

The 12AX7, 12AU7, 12AT7 preamp tubes that you will find in most 18W all have the same pinout (From the link in the previous post):


The EL84 used in the 18W has this pinout:


The pins are numbered like this:

You can check with a ohmmeter (With the power off!), the filament (heater) are the only ones that will measure a resistance.

Other tubes have different pinouts. Those you can find yourself now that we've shown you how.

[Songman68]

So like I said I can't read a schematic but I know some of those symbols.

So Pins 1 and 6 are the Plate correct?

Pins 2 and 7 are the Grid correct?

I know pins 4,5,9 are where the filaments are wired what are they called?

Are Pins 3 and 8 considered the Cathode?

Thanks for your help and quick response guys. I am in the learning process of all this and just want to make sure I understand it.

[RobPlatt]

Yes, in the 12AX7: p1,p6 are the plates; p2,p7 are the grids, and p3,p8 are the cathodes.

The symbol for Plates/anode are universally a inverted T. They attract electrons from the cathode.

Grids are a dotted line...... They scare the electrons away before they can get to the plate, and thus allow the flow of electrons to be controlled.

Cathodes are either a ] or a ). The electrons get boiled off of them.

Filaments/heaters are either a ) or a > underneath that. They are called filaments or heaters. Their job is to be warm.

Pentodes have additional grids that scare bouncy electrons back to the plate and other stuff like that.

[Songman68]

Thanks so much for the help RobPlatt, that is exactly what I was looking for and I understand much better now. I was a little lost when looking at some of the mod threads when any of the mods had to do with soldering something to the preamp tube and they would say solder to grid, plate, or cathode.

So the filament wires only serve one purpose and that is to warm. So anytime someone is talking about a mod to the cathode, they are talking about either pin 3 or 8 correct? That is due to the fact the filaments are only used for one purpose correct?

[RobPlatt]

Yes,
for the tubes we use, the filament's job is just to be warm, it doesn't carry any signal (There are some tubes that have the filament and cathode connected together, like some rectifier tubes, but don't worry about that just now. ). The wires carry a lot of current and have to be run with care to avoid that they interfere with signals that DO carry a signal.

Otherwise, most of the modifications are going to be regarding the signals connected to the plate, grid, and cathode.

[lovedat800]

you'll like this...

http://www.ampage.org/td/

[Gary]

that link is a big help. Like the original poster said, it's not often you find all the info grouped together like that.

[Defdaddy]

The pinout one-pager that Joe V at Amplates put together has been a big help to me:

http://www.18watt.com/modules.php?name= ... it&lid=170

I keep it taped to my workbench.

For the less common tubes, I like the Duncan TDSL Personal Edition, which downloads all the data to a manageable computer file which is then searchable. Follow 57 Chevy's link and you can get to it.

[Songman68]

Thanks for all the help guys, it is much appreciated.