Impressive, I have always considered the Bird slugs to be pure black magic!

Very interesting project, thanks for the upload. When I realised what you were attempting to do it struck me that the mechanical requirements would be the most challenging part to achieve but you acquitted yourself well on that too.

Here's what I'm thinking:  the slug is directional - which way you have it positioned selects whether you are measuring forward or reverse power.  So the strip serves as a capacitive pickoff which, due to the long wavelength, is a voltage sense which will always be in phase and the inductor is the current sense which depending on how the slug is oriented reverses phase.  Thus you can measure the in phase and out of phase conditions, and thus forward or reverse power.

Excellent 🎉

I repaired and calibrated a number of these Bird 43 slugs. Many times the trim pot becomes intermittent, changes resistance value due to oxidized wiper contact, turning it back and forth a few times will restore, calibrate with a known RF power source, HP 437B wattmeter

I am in awe!

Remember that you rotatr the slug to measure reflected power.  That diode combination may account for the power differential between forward and reverse power measurement.

Sweet meter!

Bird (and comparable) slugs are like eating peanuts, it's hard to stop collecting them (ask me how I know!) BTW, they can be recalibrated if needed...I have done it; see the article by K9SO in the October 2009 issue of QST.  73 - Dino KLØS

its a wonder the Chinese haven't spotted this niche in the market they'd probably knock em out $25 a piece

Always wondered why is it considered a gold standard considering the error specifications.

HI Rays-Tek MOD surplus has several of the meters for sale

The diode is a "backward  diode "    conducting  at a few  millivolts.
Definitely  not a schottky.
Unobtainable  -

Did you wind and install the coil in the same direction as the origional? I thing getting that wrong may explain the voltage reversal.

just started watching ... looks intresting i was worried about the slug you dissasebled as it had factor 10 written on it and wasnt sure if that was to be used with a bird 43 movement they made several variations of the meter and the slugs all looked similar

Please consider to sell the kits or the casing for DIY?

Did you try it at different frequencies…. Nice video.

Holy Cow are those ridiculously expensive, and even more so when one factors in the price of slugs.  About  25 years ago I bought a used Bird Model 4304A for about $250.  That has a 5-position range switch  (0–5, 0–15, 0–50, 0–150, and 0–500 watts) using a permanently installed broadband element that covered 25 to 1,000 MHz  Once I saw that, I couldn't understand why anyone would buy the Model 43.  Sure, it was (and is) less expensive than 4304A for the base meter, but buy two or three slugs and you are over the price of the 4304A.

Birds are OK, there are better units today that do the job without having to transmit full power into the antenna system,
and the new VNA styles will give you many displays, including Smith chart, for about the same price of the Birds...

Impressive mechanical skills! Your lathe and mill work is absolutely top-notch.However, I am sorry to tell you that the slug you dismantled and reverse-engineered is actually not intended for a Bird 43. The markings on your slug ("4410-3") show that it belongs to a newer and much more advanced model: the Bird 4410.Unlike the Bird 43, the Bird 4410 is an active, battery-powered instrument. It uses a single slug to cover multiple power ranges (7 steps) with very high accuracy. The reason it has two diodes facing anode-to-anode is not a manufacturing error; the second diode is used for active temperature compensation by receiving a tiny reference DC current from the 4410 housing. You can read all about this clever circuit in US Patent US4,547,728A.Because you put a 4410 circuit into a passive Bird 43 meter (which expects a direct microamp current, not a voltage reference), your reading became too low.The good news is that your mechanical housing is perfect, and an original Bird 43 slug circuit is much simpler! You can easily modify your electronics to match the true Bird 43 design. Check out the original 1958 Bird patent, US 2,852,741 (especially Figure 13), to see how the single-diode circuit should be wired.Keep up the great work, I hope you modify the circuit and get it working!