Technical Tricks & Tips

Practical notes on keeping 1920s and 30s sets working, from period articles and our own bench.

Automatic Grid BiasConverting a battery-biased set to automatic bias.Ballast Tubes & Resistance Line CordsHow AC/DC sets dropped mains voltage for their filaments, and how to replace a dead ballast.Defective TransformersReplacing an open audio or IF transformer with capacitor/resistor coupling.Magic Eye TubesBrightening tired 6E5 and 6U5 tuning indicators, and using the 1629 as a substitute.Reforming CapacitorsHow to bring old electrolytics back into service, and how they work.Rejuvenating TubesRestoring emission in pure tungsten, thoriated tungsten and oxide filaments.Substitutes for the 01AUsing type 30 and 31 tubes in place of the 01A, X99, WX12, 20 and 71A.Substitutes for the WD-11Cheap, available replacements for the WD-11 and how to build adapters for them.

Safety. Valve sets run at lethal voltages, and electrolytic capacitors hold their charge after power is removed. Work with the set unplugged and discharge capacitors before touching.