Offering a collection of parts that will convert the 3-500Z socket mounting holes in Kenwood TL-922 & probably Heathkit SB-220 linear amplifiers.
Heathkits have 36mm chassis to bottom where the Kenwood has only 25mm.
Tubes are properly cooled to better the max spec of 392 degrees F or 200 degrees C for the new tubes.
Tube cooling spec is 24 cubic meters/hour/tube or 15 cubic feet/minute/tube.
Out the 65mm diameter cooler duct size is 440 linear feet/minute or 25.5 cubic meters/hour/tube.
Kenwood stock fan will remove about 414 cubic meters/hour. Fan is flipped to pull hot air out. Included is hi-temp silicone ring good for 450 degrees F.
Loaded deformation temp of PVC is 200 degrees F. No PVC deformity has been found so far.
Fan is 12VDC 4 pin. Full speed with yellow + and black -. Tachometer output and PWM input options.
Re-tap Kenwood filament transformer from 120v to 100v to bring 10VAC filament supply to over 12.6VAC for Russian tubes.
Fan holes must be drilled larger to accommodate imperfect Kenwood to fan alignment.
Holes punched in bottom for fans are a clean 3". 2.5" might even be better. I have a hydraulic punch for either size hole.
Search Ebay for KK4NOZ & send yours in for punching. Heathkits do not need bottom holes for fan intake.