When I clean up some of my collections today, I accidentally find some tubes which I rarely (or probably never) use. Actually I have some bad habits, collecting “junks”. Not really “junks” in terms of “garbage”, but “junks” for “thing I probably don’t need or use”. Well, there is a point in my life when I should change, the time shall come… I hope 😉
For this case, they are P-Socket tubes. I got some of them, mostly AZ1 rectifier with either solid or mesh plate.
Below is the photo of the Valvo AZ1 Big Mesh on the P-Socket, then converted to Octal base. How to make it? Let’s continue.
First, we have to understand the basing of Octal and P-Socket. I’m talking for rectifier type tube, not for the triode or others. Since I don’t see any reason to use converter, except for rectifier tube.
The Octal socket for rectifier tube has 4 major pins, the pin #4 and #6 for anode/plate, while pin #2 and #8 for heater/filament (some indirect heated rectifier will use extra pin, but they are out of my scope in this topic). Meanwhile, the P-Socket will use pin#2 and #3 for heater/filament. For anode/plate, the pins are #5 and #8. Please be noted that below layout must be seen from bottom (bottom view).
Once we have understood the different, we just simply need to connect the Octal socket to the P-Socket. Off course, we have to connect at proper designation for each pin. Please double check before you connect. I don’t want to see someone put 600 VAC into 4V filament pins 😉
For filament connection, use at least 1.2 mm or more copper solid core wire (1.5 to 2 mm recommended), since this filament will need to cover at least 1A current (up to 4A on some high capacity tube). Meanwhile for the anode/plate, you can use smaller but higher quality cable. Silver and stranded also fine if you have the budget. Also consider a good insulation, since big chance that we are playing with 250 VAC or more with Center Tapped transformer (500 VAC or more end-to-end).
Once you have confirmed the soldering quality and no short, you can start testing this converter.
This P-Socket to Octal converter actually not really a good example, since most Octal-based rectifier will use 5 Volt filament, while P-Socket probably will need 4 Volt. Don’t ever think to use Resistor as voltage dropper. Believe me, it will not work for most of your purpose. If you still insist, make sure maximum allowed P-Socket Rectifier tube used is the one with 1A filament current consumption. This is maximum, so no more! You can start with 0.5R Dale 6W Resistor, put on both filament pins. This will make a 1R resistance and produce 1 Volt voltage drop at 1A current.
If you think that you can use 2A Rectifier, by changing the resistor to 0.25R Resistor on both filament pins to maintain 1 Volt drop at 2A current, they you are totally wrong! I’ve been there, the final voltage will drop under 4 Volt and the 6W resistor will be hot enough to burn your finger. I used totally 24W resistor (0.5R in parallel on both filament pins). The temperature was fine, but the filament voltage dropped to under 4V, so it didn’t produce enough voltage to fire up my Rectifier to work properly.
On my system, I use two sockets (Octal and B4), and I have a small switch to pick the filament voltage either 4 Volt of 5 Volt. The voltage is pure from the secondary tap on my main transformer, not by using Resistor as voltage dropper.
We can expect small comparison test from P-Socket Rectifier tube (AZ series) vs the B4 tube (RGN series)… later 😉