With what PID cost, now it's no longer worth buying a furnace with electronic temperature regulation!
I built various furnace: the cheapest I built it using an old fryer, which my daughters had thrown away! It was perfectly functional, but for them ... it smelled of fried oil!
I took it apart, I made a solid base with a piece of steel tube and threaded rods, I mounted the furnace, and on this I mounted a PID.
I recommend the PID INKBIRD ITC 100: it is the only one I found the user manual!
https://pmod79883-pic31.websiteonlin..._Manual_V1.pdf
It is typically sold in a kit that includes a K thermocouple and a uxcell Heat Sink + Solid State Relay SSR.
They are found on Amazon:
https://www.amazon.com/Inkbird-Therm.../dp/B00SH1VQZ2
https://www.amazon.com/uxcell-Solid-...2aa-11e8-a54c- a93e233805e9 & pd_rd_w = GkfjL & pd_rd_wg = b95zy & pf_rd_i = desktop-dp-sims & pf_rd_m = ATVPDKIKX0DER & pf_rd_p = 6725dbd6-9917-451d-beba-16af7874e407 & pf_rd_r = 9B33YATZBEVJBHXK1GKA & pf_rd_s = desktop-dp-sims & pf_rd_t = 40701 & psc = 1 & refRID = 9B33YATZBEVJBHXK1GKA
https://www.amazon.com/Uxcell-a12031...e-Temperature-
Controller / dp / B00899A4LY / ref = pd_bxgy_328_img_2? _Encoding = UTF8 & pd_rd_i = B00899A4LY & pd_rd_r = f140bf45-e2 AA-11e8-a875-091c391444d5 & pd_rd_w = 29yRQ & pd_rd_wg = o96NP & pf_rd_i = desktop-dp-sims & pf_rd_m = ATVPDKIKX0DER & pf_rd_p = 6725dbd6-9917-451d-beba-16af7874e407 & pf_rd_r = Z1E4B591XZ6685W7Y3DH & pf_rd_s = desktop-dp-sims & pf_rd_t = 40701 & psc = 1 & refRID = Z1E4B591XZ6685W7Y3DH
Then in another furnace I mounted a lead regulator, which has up to 6 outputs (for the 6 CV Molds)!