[Boatanchors] Has anyone ever cut the glass top off a miniaturetube to re-use the base?

[Drew P.]

Dale Parfitt wrote:

"I will look the tube up- tnx.
The only one I have done is to replace OA2's etc with the little TO-92 HV 
regulators= LR8N3. Better regulation and less heat.
http://ww1.microchip.com/downloads/en/DeviceDoc/LR8%20B080113.pdf"


This 3 terminal high voltage regulator is a good find, Dale. Viewing Microchip's site with link you provided, I see that the LR8 is also available in a larger package for higher power dissipation.  It looks like in using the LR8 to replace 0A2 and its ilk, you changed the circuit topology from shunt regulation to series regulation - definitely less heat. 

Most VR tubes have multiple pins connected to each element which allows the load current to be passed, if desired, into one pin and back out another. With such connection, pulling the VR tube disconnects the load.  This would be handy in an LR8-based tubester, you would pass the load current into one pin, through the LR8, and out another pin.  You would get the aforementioned topology change without having to modify the equipment.  Being able to use a drop-right-in-with-no-mods-required tubester would, of course, require that the equipment had the VR tube connected in the pass-through mode. If not, then a minor mod of rewiring at the VR tube socket would be required, and the original VR tube then still could be used if desired.

Drew