This linear amplifier design dated back to the early-1960's. It uses four 811A (or 572B) tubes for up to 1KW input power for 70W drive. This unit had let out some 'magic smoke' when the owner switched it on. The fault was identified as a wiring error made by someone during component replacement causing an electrolytic capacitor to fail. This was corrected, a new rectifier (voltage doubler) board fitted, several other parts replaced and the tubes tested (all good). Not having a suitable 'exciter' to drive the amplifier, the demo only shows that the unit is delivering the required pate voltage (2Kv) - with no smoke!
![](https://i.ytimg.com/vi/Q77aVE0OdZk/maxresdefault.jpg)