Tag Archives: psvane 845T

How is 845 like when dead?

Some forum members had a shorted tube – here is a picture of how it looks like (credit to AudiogoN member ‘amfibius’) when the event happens:

Here are some explanation from Psvane tube engineer about the event:

1. The short (lighting show you have seen) on 845 tubes is caused by residual air in the vacuum tubes act with active materials on the cathode. When active materials (electron emission coating on the cathode) become detached from the cathode under extreme heat (1000V), it will act with the residual air in the tube causing a short (lightening arc). The residual air may not be present at factory final testing when the tube leaves factory, but during shipping/handling/or usage with time, very tiny amount of air could leak into the tube, especially these large sized vacuum tubes.

2. Very few tube factory still make 845 tubes nowadays – as far as I know, only Shuguang in China and KR Audio in Europe. KR 845 tubes have quality problems too such as red plate caused by over current, so Shuguang 845 tubes have been used on most modern 845 tube amps. Shuguang made a few different design 845 tubes in the past – including a metal plate 845C. The metal plate 845C tubes were considered best sounding among all past models but the metal plate soldering cannot handle extreme heat well, so historically there have been very high percentage failure rate (nearly 50%) so the metal plate 845C tube has disappeared from the market now.

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