arc V70 blue flash in KT90 tubes

[muizel]

Hi,

I have an arc V70 wich is operating flawlesly, but I noticed when I shut down the power in all 8 KT90 tubes I see a small blue flash just like a high voltage spark, is that normal ? I put in 8 new valves and it makes no difference.


I hope someone can help me out on this.


Rehards René.

 

[richwalters]

Bit late responding to this. We need a circuit diagram to get further.

richy

 

[Miles Prower]

Need to have a look at the power supply schemo. That looks like some sort of high voltage pulse that's somehow occurring on power down. Any interruption of current through inductance is going to cause flyback. Don't know why it's happening with that amp.

 

[rknize]

My guess would be the bias supply is collapsing long before B+. The blue flash are the tubes going into full conduction while B+ discharges.