Anyone use a 5687 with adapter in place of a 6922/6DJ8/7308/6N23P?

At 6.3V heater current for a 6922 tube is 0.3A

https://frank.pocnet.net/sheets/049/6/6922.pdf

.

At 6.3V for a Raytheon 5687 tube heater current is 0.65A

https://frank.pocnet.net/sheets/138/5/5687WA.pdf

What is the VA rating of the 6.3V winding of the power transformer in the equipment the Raytheon 5687 will be used in? Care must be taken not to overload the winding causing it fail, burn up/short out. Power transformers can be quite expensive to replace. Also may not be available anymore. 

Gary Dodd’s preamp? You might want to try and speak to someone, tech support if possible, before trying the 5687 tubes in the preamp. 

thinking the circuit controls how much voltage gets to the tubes, not the voltage of the power supply...essentially I’m thinking that the circuit functions as a voltage valve that doesn’t care how much amperage is in the tank as long as it’s enough pass the valve’s design flow. 

 Heater 6.3Vdc voltage should be constant. It should not vary. It may even be regulated. How is the 6.3VDC created? Any idea of the circuit? Voltage divider? If a voltage regulator is used to maintain a constant 6.3 DC voltage, will it handle over twice the current of the two 6922 heaters? The preamp was designed for two 6922 tube heaters. 0.3 amps each tube heater.

Current should pretty much be constant through the heater filament of each tube. Maybe a slight inrush current on a cold start up but settle down to normal quickly. 

Ohms Law is at play. I = E / R

I (current) = E (voltage) / R (Resistance of heater filament) 

.

How many of 5687 tubes is used in the equipment. Just one?

You could increase the AH rating of the battery. 

The 5687 draws over twice the heater amps as the 6922 tube.

Did you read the part where it says the glass envelope of the 5687 runs hot. Care must be taken.

.