04-01-2016, 01:19 PM
The diodes are most likely there for protection.
If the regulator LM317 should short, it would put the full unregulated DC voltage into the 1.4V filaments of the tubes, instantly blowing them out. The three diodes effectively clamp the output voltage to a max of 2V or so, thereby protecting the filaments from possible destruction in case of regulator failure.
If the regulator LM317 should short, it would put the full unregulated DC voltage into the 1.4V filaments of the tubes, instantly blowing them out. The three diodes effectively clamp the output voltage to a max of 2V or so, thereby protecting the filaments from possible destruction in case of regulator failure.
![[-]](https://philcoradio.com/phorum/images/bootbb/collapse.png "[-]")
