This is going to be instructions how to make "THE PRO BOX" adapter to use 6.3v and 12.6v heated double triode tubes with your Little Dot headphone amplifier. This shows how to make adapter to Little Dot MK II. With MK III and MK IV this is not going to as easy.
Do not try to do anything like this, if you don't know what you are doing!
To do box like this, you need:
Suitable electric box, like Hammond manufacturing 1591MSBK
9pin ON-ON or ON-OFF-ON switch 3PDT
2 B7G tube pin protector/straightener, ebay-seller yitry have these
1mm or 18gauge thick copper wire as pins
Epoxy and gel super glue
Tools you need at least:
Soldering iron and something to solder with
Here is how the pins are going to be connected:
Left B7G Box B9A Right B7G
5 - 1
1 - 2
2 - 3
3 via switch to 4
4 via switch to 5
6 - 5
7 - 1
8 - 2
9 comes from the switch
Here is the same drawn. And you see how the switch is connected.
Here are the most of things you need to make it. 1mm (18gauge) thick copperwire for the pins what i used was covered with lacquer, so it needed to be removed first by grinding.
Here are the parts for the pins. B7G socket is just to keep pins more straight when gel super glueing pins through the pin protector/straightener. I grinded wire heads more round.
Here is the assembly waiting for drying.
I made holes to bottom of the box. Paper is there protecting little dot from getting any epoxy. You just push pins through the paper. I glued parts together with epoxy. If you do not do this like this way, it is hard to get pins go to you little dot sockets.
This shows the extra wires that are needed with the switch.
And how the switch is connected to the B9A socket. B9A socket is already glued to top of the box.
Soldered all the rest wires. Cutted those additional copper wires shorter after taking photo. Make sure all connections are ok with multimeter after closing the box.
And here is the box in use. There needs to be at least 1cm or 3/8in space between box and powertubes.
Most of the compatible tubes won't care if the switch is in wrong position, but there is couple 6.3v tubes that could be used in 3.15v heater voltage system with pin9 connected as "ground". So you need to be careful to not burn heaters broken.
Adapter like this should work with LD models MK I+, MK II (newest model), MK III and MK IV (+SE).
Edit 1: Added shield wiring to diagram for 6DJ8 and 6922 tubes. At least those tubes are going to hum without this connection. You can add ON-OFF switch between this connection too.
Edit 2: With MK III or MK IV this not as easy as this.
Edited by Artsi - 11/9/13 at 2:41am