Originally Posted by KimLaroux
Considering you only need to change a single resistor for the 12AU7 version, why did you not simply modify the kits to use 12AU7? I'm sure there's still a market for it.
Sure you have to modify the board for the 9 pins socket, but it's not like you had to redesign the whole chassis.
Are there still boards left for the 19j6 version? they could be hacked to use a 12au7....
Sorry, but modifying a PCB for a 9-pin socket is like re-designing the entire PCB.
Pins 1 and 6 are the plates on the 12AU7, whereas pins 1 and 2 are the plates on the 19J6.
Pins 3 and 8 are the cathodes on the 12AU7, whereas pin 7 is the single cathode on the 19J6.
Pins 2 and 7 are the grids on the 12AU7, whereas pins 5 and 6 are the grids on the 19J6.
Pins 4 and 5 are the heater on the 12AU7, whereas pins 3 and 4 are the heater on the 19J6.
It looks to me like pins 1 and 4 are the only pins that are the same. This is a PCB we're talking about, here, and not a very complicated one at that. Once you completely change up the pins on the tube sockets, you've completely changed the PCB.
I didn't intend to get into this in detail, but maybe I should since I receive a note or two every other week on whether there are any Starving Student kits. There are other issues besides the scarcity of the 19J6.
There has been some thought to bringing out a PCB for the 12AU7. It could happen sometime in the future. However, the 12AU7 is an entirely different tube than the 19J6's and flies in the face of the "Starving Student" principle. The 19J6's were $1-$2 tubes when things started out. The 12AU7's have never been that cheap and there's a school of thought that perhaps a more robust amplifier design is appropriate for a 12AU7 (there are many existing examples). Yes, it's fine to have a point-to-point with a 12AU7 if you really want to build a Starving Student and we documented that variation for posterity on DIYForums.org. However, basing a manufacturing run with a completely different pinout on a much more expensive/capable tube is a different matter.
There's also the issue of the power supply. I hate to remind everyone, but the Starving Student with its original "surplus" Cisco power supply was/is responsible for frying a number of DACs, including up to 3 of my own. That's another factor that has to be taken into account when investing major bucks in manufacturing runs of PCB's and machined cases that could be potentially liable for the destruction of customers' sources. With $1-$2 tubes and a $7 power supply (another cost that didn't hold), maybe it was worth that risk. If those costs don't hold, then maybe not ...
Edited by tomb - 12/23/12 at 1:21am