24V guitar amp

[El Heisenberg]

Is it the 12ae7?

[iccaros]

It does draw more current..
can you put a drawing of the heaters.. I am using a 2amp one right now, and using (2) 12ae7's does not make the transformer drop

I have pin 4 to + 24
Pin 5 to Pin 5 of the next tubes heaters
then Pin 4 of that one to ground.

But they are the same type
The 12k5's are on there own heater chain.

[El Heisenberg]

[El Heisenberg]

I will draw out how they are physically wired or take a picture later.

The two 12K5s are next to each other. The 12AE7 is next to one of the 12K5s. so it's an L shape. I attached the CT and ground wires to pins 3 and 4 of the 12K5 next to the 12AE7. From there two twists of wires go to the 12AE7 and the other 12K5. This is was just the easiest way to wire the extra tube without disassembling the entire amp.

[iccaros]

so the 12ae7 needs a resistor to drop about 12volts so a 42 ohm.. It may have to be a 5watt  (.3 amp * 12 = 3watts something.... )

the 12K5 are good, and this way two tubes use the same amount of current as one..
I have 4 tubes so its simple..

[El Heisenberg]

Nanything else i can try?

[iccaros]

I am lost.. sorry, if you have the 12.6 -0 - 12.6 transformer

Then with a half bridge rectifier, your voltage is right.. you will need a full bride to get 24 volts.. you'll see 33.84 rectified.. (voltage * 1.41) this is what I was using to start with.. Now I use a 24 volt 1.8 amp wall plug for a gateway computer I got at Good will for $1

[El Heisenberg]

Yea I wanted to keep things in the package tho. All self contained. I built the thing into a gutted "optimus" radioshack brand guitar amp.


I'm seeing like 32v before the RC filter. Same as B+ when it starts up, but when the tubes heat up and the amp starts running its down to 24v.


This is WITH the 12U7 too. So it's not the 12AE7! AAARrrhG!!

[El Heisenberg]

So i have to put a resistor there so that the resistance of the 12ae7s heaters is the same as the 12k5 X2 heaters??

Why does it hav to be such a high wattage? Cant be two watts?

[iccaros]

 12v * .3 amp (watts = V* I)   = 3.6 watts
The tube will draw .3 amps it has to go through the resistor.

http://www.csgnetwork.com/ohmslaw2.html

[El Heisenberg]

well screw finding a 42 ohm 5 watt resistors. I'm just gunna use 2 x 22 ohm 2 watt resistors is that fine?

[iccaros]

sure...

[El Heisenberg]

Eh stuck the 47 ohm 5 watt resistor in there and all it did was drop the 12ae7 heater voltage to 2.7 volts.

[El Heisenberg]

 Guess 24v isnt bad. It IS a 24v power supply anyway. I was worried i was losing volume since voltage was being dropped

[iccaros]

Eh stuck the 47 ohm 5 watt resistor in there and all it did was drop the 12ae7 heater voltage to 2.7 volts.

My fault.. Misread the data sheet.

Or the wrong one..

So the datasheet says it drops .450 ma @ 12.6 volts..
so 12.6 / .45 = 28ohms.. That is why you dropped so much.. sorry..

[iccaros]

Guess 24v isnt bad. It IS a 24v power supply anyway. I was worried i was losing volume since voltage was being dropped

I'm running 24 volts.. I plugged into my 4x12 and ... WoW.. !!!..

[El Heisenberg]

Guess 24v isnt bad. It IS a 24v power supply anyway. I was worried i was losing volume since voltage was being dropped

I'm running 24 volts.. I plugged into my 4x12 and ... WoW.. !!!..

Yea its crazy loud out of a full cab.

Are you running the 12k5s at 24v too? I havent had any failures like you said u have and i left mine on overnite on accident!

[iccaros]

I am, my grid is @ 12v but the plates are on the 24v line.

you may not, 3 out of my 5 tubes had no issues.. But those tubes sounded like a tremolo was on..

[El Heisenberg]

Hey, i put in a 22 ohm 5watt and now the 12AE7 heaters read 6v AC.

Was it sposed to be .22 ohm??

Either way my B+ still drops to 24v from 30v

[El Heisenberg]

Hey maybe ill just use a full wave rectifier and and get 36v.

I could still use the center tap to power the heaters, yes??