enter image description hereenter image description hereI have a vacuum tube and need help working out what it is. The numbers on the tube are APW 8047 it 4 pin and fits in a B4 socket. I wasn't able to find it with a Google search of the number. Are there any resources that let me look it up? All found out it was made around 1944 and i think it may have bin used in a radar set up that's all i know i had a much closer look and it does look like it does have a heating element in it looks like its sum sort of switchif you can see they a lot of thin wires in it

  • 1
    $\begingroup$ 8047 looks like a date code (year 80 week 47) so that might not help. Can you provide some context like what's it from? and maybe some hi-res pictures? Edit your post to include your additions. $\endgroup$
    – mike65535
    Jul 3, 2022 at 18:20
  • 4
    $\begingroup$ Help us out here... Something less blurry perhaps? From several sides? $\endgroup$
    – mike65535
    Jul 4, 2022 at 15:33
  • 6
    $\begingroup$ That's not a normal tube like a triode or pentode, it appears to be something mechanical in a vacuum housing. It looks like it could be a thermal time delay, does it appear to have a heating element in it? $\endgroup$
    – GodJihyo
    Jul 5, 2022 at 6:18
  • $\begingroup$ I looks like a ballast tube (Resistor). $\endgroup$
    – Gil
    Jul 24, 2022 at 1:35

1 Answer 1


This is very likely to be a thermal time delay relay, as suggested by @GodJihyo.

Two of the pins warm the heating element, and the other two pass the signal if the switch is enabled - usually with some sort of bimetalic strip. Some are design to engage when warm and others to disengage when warm.

The numbers on things like this that I've seen before usually indicate voltage for the heater and how long the delay is, but 8047 doesn't seem like a good fit for that - 47 seems like an odd number.

If you can deduce which pins warm it up, you could start with a low voltage, see if you can make it work :)

As a suggestion, perhaps rename this question - it sounds like you're asking for general advice on identifying valves/tubes, whereas this is a specific "what is this" question, I feel.


You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .