12 VDC heaters confirmation

[Guitarist]

I think this should work, maybe? I've got two 12av7s.

4 to ground
5 to 12 Volts +
9 not connected

run heaters in series 5..4..5..ground

Using EH 12 volt transformer wall wart. The DC is well filtered without any series resistors. Add 470 Ohm on the 12 V?

We need a sticky/offficial chart for these filiment wiring options. Thanks,

[Enzo]

Though we usually wire them up for 6 volts, the tubes are actually 12 volt tubes, hence the 12 in 12AV7. The "center tap" allows the flexibility. it is right in the tube data manuals.

You can even wire tube heaters in series and run them off higher voltages. For example if you have existing +24 and -24 supplies, you can wire four 12AX7s in series across the two supplies. In the Peavey Classic 30, the power tube heaters are wired in series, and the preamp tube heaters are separately wired in series too.

What would be the purpose of your 470 ohm resistor?

[Guitarist]

OK, I was thinking that a 470 Ohm might add some choke style properties. I noticed with this preamp that there was major hum without it on the B+.

With the att. pic it looks that for two tubes on 12V run them in parallel, don't connect pin 9 but float the ground (pin 5)?

I did look at a Peavey schematic by found it hard to figure out the heater patterns.

I'm going the Electro Harmonix route alike their tube pedal lines. I've got a couple of their pedals but am too cautious to fully pull them apart.

Aside, I included you on the "charts and transcriptions" email I just sent out to friends and students thinking you might find such useful. You've aways been very helpful to folks and I'm sure you receive a lot of chocolate this time of year!

edit: Works (meaning sounds good). PIn 9 n.c., pin 4 +12V, pin 5 rectifier "ground", pins 4 and 5 referenced to ground with 39 Ohm resistors ala B**gie, pins in parallel.
Question how does 39 Ohms not short out 12 V +'ve? Why does this help hum?

[Enzo]

To heat one 12AV7 tube on 12v heater current, you connect pins 4 and 5 across the 12v and 9 is not connected at all. Doesn't matter which way - ground pin 5 and +12 to 4, or ground pin 4 and +12 to 5.

Two tubes? Wire them all the same. COnnect all the pins 4 together, and wire all the pins 5 together. Then connect 12v to them.

Let us get away from calling pin 4 or 5 ground or any other name. It is just a coil of wire inside the tube, and it gets hot when current flows through it. It might as well be a resistor. In your particular circuit, one side might be grounded. In the typical AC heater circuit, we usually ground the center tap, or create an artificial center tap. But on some amps, especialy older ones, one side was grounded.

In a tube amp, you might replace a choke with a resistor, but the resistor itself is not doing the filtering. That you have then is two filter caps with the resistor betweeen them. The resistor serves to decouple the caps. SO two caps with that resistor between them will filter better than two caps in parallel. The only reason I might add a resistor here would be in the case that your wall wart put out too much voltage. The voltage it makes without the load connected is irrelevant. COnnect it to the tubes, and measure the voltage on the tubes. It should be close to 12.6, you don't want 14 or something.