• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Do 300b tube have a "guide pin"


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Some have guide pins, but many do not, worse when present they are not necessarily in the right place. I would avoid using vintage sockets with 300B unless you are sure the pin is not going to cause an issue.

JJ300B have guide pins, but I am not sure whether or not they are in the same location as a reference WE300B - I no longer have any WE to compare..


2012-08-15 8:24 am
My JJ 300Bs have a black dot where the guide pin is supposed to be. It could be that later production has a real pin there (mine are around 15y old).
I remember the Chinese versions from the late 90s all had guide pins so they could be used in the (Chinese) twist lock sockets.
I don't think I ever saw such a socket in an amp though, only on the shelf in the shop.
I built a DIY amplifier that used a 5Z3 - a 4 pin rectifier. During the initial build I used some cheap knockoff of the classic Johnson Ceramic socket.

I found that it was possible to insert the tube incorrectly, the tolerances of the small pin holes were loose enough that the big pins could slide in.

I ended up replacing the socket with an octal one and using the 5U4.
Ha! I should have waited for your answers!

I did in fact insert 3 out of 4 Electro Harmonic wrongly (into a Chinese amp). Now 3 out of 4 test bad in my tube tester. When I plugged them back in, this time correctly, the channel with 2/2 testing bad plays low, the channel with 1 out of 2 testing bad, plays at higher volume.

I guess I'm in the market for some cheap 300b replacement then :/