Ode to the 8416

I hate 6.3V heaters. More specifically, if any sort of reasonable current is needed, it is more or less impossible to get 6.3VDC out of a 6.3VAC winding. This is not news, of course. Using a 12.6VAC winding instead with a regulator results in a ton of heat needing to be dissipated from the regulator and thus a big heatsink, which seems like a terrible solution too. A 12.6VAC winding, on the other hand, will supply 12.6VDC just fine, and the lower current further reduces the need for heat dissipation. And, 12.6VAC transformers are available for about $4 at the radioshack across the street from my house. And, 12.6V versions of popular tubes are available for a ton less money -- NOS 12SN7's are a steal.

So, I decided a while back that anywhere that I couldn't use AC heaters due to noise that 12.6V heaters were in order. To that end, I was looking for a tube to replace the gain stage in my DAC. It previously has used 6N6p's, 6N1p's, 6922's, and a few others, but the heater has always been an issue. The circuit is basically just a CCS plate loaded grounded cathode. The DAC chip (AD1865N-K) uses a passive I/V and feeds the signal directly to the grid.

On a lark, I searched for 12dj8 and stumbled upon the 8416 -- I think I found an ebay seller claiming they were the same. Other than that, I think I found one post here mentioning the tube, and a handful at a few other forums, and some references to its use in scopes. But, this tube does not seem to be in wide use i naudio, though every montion of it is positive. I couldn't even find a datasheet anywhere.



As far as I can tell, the only 8416 available is an amperex pq that seems to sound every bit as good as amperex 6dj8's I've owned for a lot less money -- like 90% less. As shown in the picture, there are orange and white labels -- I got an orange one with a late 70's date code. I have no idea what the difference is. The pins are gold, and otherwise it looks just like a 6dj8. Its a good tube, and available from most of the usual suspects.

-d