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I was sitting here looking at all the old chassis and transformers I've acquired over the years and thinking it would be neat to make a transformer test rig so that I could have a better idea how something would perform before using it. So many of these old transformers were designed with lower line voltages in mind and I suspect they're unusable these days. A conservative and usable 700vct transformer from 35 years ago now might put out 800+VCT with today's 122 line volts in, enough to make it much less usable and too high a voltage to use with a 6 volt tube rectifier. I suppose there are zener tricks and the like but it's tough to use them without knowing!
I was thinking I could use an old steel chassis and mount a screw type through-chassis terminal strip with connections for line AC, 5 and 6.3 volt fils and plate supplies. I'd probably use a largish (internal) heatsink with a bunch of IRF810's (or similar) and a small PWM circuit and a fan to load the plate windings with the option of selecting 5 or 6.3 volt tube or silicon rectifiers and 20-100uf filtering. Tube sockets would allow swapping rectifier tubes to duplicate actual circuits.
Small dropping resistors (1 to 10 ohm) in line with the various parts would allow me to easily insert a test point so that I could measure the current delivery. The transformer would be out in open so I could easily make sure that it isn't overheating. Filament connections would be exposed so I could make sure there was sufficient voltage going to them.
The only thing I'm concerned with is how to properly load the filament windings. It would be easy enough to wire a bunch of tube sockets so that I could just plug in whatever tube complement I'd want to use for a given amp project but I wonder if a bunch of power resistors on switches would achieve the same thing with less soldering.
As usual, not an expert, just a tinkerer with some crazy ideas. Any thoughts?
jamie
I was thinking I could use an old steel chassis and mount a screw type through-chassis terminal strip with connections for line AC, 5 and 6.3 volt fils and plate supplies. I'd probably use a largish (internal) heatsink with a bunch of IRF810's (or similar) and a small PWM circuit and a fan to load the plate windings with the option of selecting 5 or 6.3 volt tube or silicon rectifiers and 20-100uf filtering. Tube sockets would allow swapping rectifier tubes to duplicate actual circuits.
Small dropping resistors (1 to 10 ohm) in line with the various parts would allow me to easily insert a test point so that I could measure the current delivery. The transformer would be out in open so I could easily make sure that it isn't overheating. Filament connections would be exposed so I could make sure there was sufficient voltage going to them.
The only thing I'm concerned with is how to properly load the filament windings. It would be easy enough to wire a bunch of tube sockets so that I could just plug in whatever tube complement I'd want to use for a given amp project but I wonder if a bunch of power resistors on switches would achieve the same thing with less soldering.
As usual, not an expert, just a tinkerer with some crazy ideas. Any thoughts?
jamie