DIY Vacuum Tube Tester for Audio Tubes

DIY Tube tester; I first saw the excellent and simple Valve Heaven tester design on the net but I couldn't get a suitable transformer off the shelf and I didn't like a few of the features. I stumbled upon the Electronics Old & New channel which nicely documents their tester design which is excellent (I liked it a lot so my tester takes a lot from this design). I decided I wanted DC heaters with adjustable voltage via a trimmer, but I could also use a bunch of fixed value resistors on the ADJ pin of the LM338 regulator to get 5v, 6.3v, 12v and 15v. The bias uses an LM317 and adjustment is done via 5K Bournes multi turn pot (should be really accurate). All metering is done via external multimeters which simply connect via the 4mm plug sockets (Panel meters of the non Chinese type cost more than a reasonable multimeter, and when you're done testing valves you can use the multimeters for whatever, I've got a couple of large meters but found I can't accurately read analogue meters although these do look cool!). Three sockets should test the majority of common valves I find in the guitar amps I service, I also have a forth socket which I can internally patch for any other valve as required. I incorrectly said n the video the plate Voltage is 180; it's 280 and fully adjustable as in the screen. the bias should go down to minus 35v if required and the heater can go up to plus 35 if needed. Future mods could be an adjustable Plate load value and Cathode load value via pots.
Another interesting channel I found was the Helge Fykse who adopted an audio input and output circuit which enables you to both inject a waveform to G1 and listen and/or monitor with scope at the output jack.