Getting more voltage out of tube heater filament?

[Jdansti]

Any rectification?  Make sure you have DC coming out.

[blues_mang]

It is (was) a 120V AC to 9V DC wall wart, so it must rectifying it (possibly under the goop on the transformer?).

[MetalGuy]

There's no need to rediscover the wheel! Voltage doubler and regulator from 6V3AC heaters as found in Mesa Mark IV:

[Jdansti]

^ Just curious. Does it say C441-443 8200 uF?

[MetalGuy]

Yes. However it works with lower value caps as well.

[blues_mang]

That looks easy enough to build on a little piece of perf or stripboard. My schematic reading is a little rusty, but I'll do up a layout and post it to make sure I'm correct. The only thing I'm not sure of is which pins this is connected to. Is it pins 4 and 9 like I originally connected?

[MetalGuy]

When running 12A_7 tubes' heaters at 6V3AC you should connect pins 4 and 5 together and apply voltage to pin 9 and pins 4/5 respectively take voltage from there.

[blues_mang]

It looks like on the schemo and on the PCB for the Firefly, pins 4 & 5 are already connected together. That would explain why I'm already getting 6.3VAC from connecting to pins 4 & 9. So that part is set, I just need to figure out a layout for the rest of it and get a hold of some VR9's.

[davent]

It looks like on the schemo and on the PCB for the Firefly, pins 4 & 5 are already connected together. That would explain why I'm already getting 6.3VAC from connecting to pins 4 & 9. So that part is set, I just need to figure out a layout for the rest of it and get a hold of some VR9's.

Are you using the Calhoun Firefly pcb or another with pcb mounted sockets because if not ... you have to connect pin 4&5 for 12a_7 tubes when heater powered by 6v3, one wire to 4&5 the other to pin 9. If you're powering with 12v6  you connect one wire to 4  and the other to 5.

John posted the tube pinout earlier in the thread for reference.

Here's the goto Firefly layout, showing correct heater wiring for a 6v3 supply.

http://www.diyguitarist.com/PDF_Files/FireflyChassis.pdf

[blues_mang]

I'm using the PCB in the link on the first page purchased from a forum member a while back. The sockets are pcb mounted and the pcb clearly shows a trace connecting pins 4 & 5.