[disclaimer] if this isn't the right place for this content, feel free to move/delete
I just recently finished restoring a wire recorder - Webster Model 80 - and thought it migt be an interesting subject in here on "old school electronics" - i.e. tube based stuffs. I ran into some issues along the way, but most of them were actually more mechanical than electrical. I ended up replacing most of the components, as the age was getting to them. To the best of my knowledge, the device was made around 1947 so some dead capacitors are to be expected.
I learned quite a bit about tube amplifier circuits in this; still not quite sure how that record bias oscillator works; I can identify the relevant components, but I'm not quite sure what makes it tick... maybe somebody on here has a few pointers? I'm pretty well versed in DC and digital circuitry, but when it comes to higher frequency stuff or even RF... it's... magic.
I found it interesting that the service manual already talks about "wow and flutter" - when the speed of the wire is 100% dictated by the mains frequency and a simple shaded pole motor with some rubber wheels pulling it along... not even anything resembling the "capstan/pinch roller" of a typical tape deck.
The project video (including my usual "special" presentation style) is available here - along with the mechanical parts.
EDIT: moved video link down because of preview image.