9V tube pedal: should the heaters glow?

[nee]

Hi all!

I'm familiar with tube amp topology and tube theory so I thought I'd try a low-voltage tube stompbox, along the lines of the ValveCaster.

I'm using a 12AX7 with a 12VDC supply to pin 4 of the tube, pin 5 to earth. Should the heaters be lighting up the way they do in a tube amp? The 12V supply is rated for 1000mA. There's 12V at pin 4, pin 5, and pin 9. The tube seems completely dead! I've tried others too!

Thanks!

[frequencycentral]

The heaters should glow - but not too much.

In the Valvecaster, pin 4 should be earth, pin 5 should be +12volts - you have it the other way around. I don't know if that matters.

Pin 9 is the heater centre tap. You should leave it with no connection. The voltage at pin 9 should measure at half of whatever your DC supply is. Have a look at voltages I posted on the Dano12's Valvecaster thread: http://www.diystompboxes.com/smfforum/index.php?topic=63479.760

If pin 9 is unconnected and you're still measuring 12 volts there's a problem. There should also be a small amout of resistance between the heater connections (take the tube out of the circuit to measure), 4, 5 and 9 - just a few ohms. if there's no resistance that would explain 12 volts at pin 9. Bad heater.

[frequencycentral]

Bump for edit.

[served]

I got 60 and 30 ohms between them. Im not sure which it was, my multimeter is injured a little.

But do they have to glow blue or orange?
I bought new Ecc82 but they dont glow blue, only orange.

[morcey2]

If you've got 12V on both 4 and 5, the ground isn't connected somewhere.  Pull the tube and measure the resistance between pin 5 and the ground point on the power supply.  If you don't have 0-ohms, something isn't connected right.  If you have continuity then something is wrong with the power supply and it's connections.  They tubes are probably fine. 

As for the blue vs orange glow,  preamp tubes almost never glow blue.  The only glow you'll get inside a 12AU7 should be a little tiny bit of orange inside the center of each triode, usually only visible near the top or bottom of each assembly. 

Matt.

[served]

ohh, then my heaters are working just fine

[nee]

Thanks for your input everyone. This had me tearing my hair out for several hours. I finally discovered there's a fault with my breadboard - a break in the internal connection on the rail I was using for ground. Aaargggh!!!! I now have beautifully glowing heaters!

IanG

[kurtlives]

Thanks for your input everyone. This had me tearing my hair out for several hours. I finally discovered there's a fault with my breadboard - a break in the internal connection on the rail I was using for ground. Aaargggh!!!! I now have beautifully glowing heaters!

IanG

Shi t like that just pisses me off so much...

Nice catch!

[snap]

Thanks for your input everyone. This had me tearing my hair out for several hours. I finally discovered there's a fault with my breadboard - a break in the internal connection on the rail I was using for ground. Aaargggh!!!! I now have beautifully glowing heaters!

IanG

not a breadboard fault, but probably a built in break:
http://www.diystompboxes.com/smfforum/index.php?topic=56370.msg435201#msg435201

[nee]

not a breadboard fault, but probably a built in break:
http://www.diystompboxes.com/smfforum/index.php?topic=56370.msg435201#msg435201

No, it's definitely a fault. There is a break in the centre, but my fault/break is halfway along one group of five terminals.