Has something like this ever happened to your el84? A spark in pin 7 and at the same time a crack in the glass of the tube in the place of pin 7.
if the load is separated from the output and a sudden signal enters, this spark will generate in the power tubes. But in the case of el84 The lovely tube needs to be replaced. as you know ....The cause of the spark is the production of high voltage in the primary choke.
Keep speaker wires connected. make sure they don't disconnect as this may cause a huge overvoltage. In this case you are
happy since only the tube is damaged and the transformer is ok. Tubes are easy to replace transformers not so.
It looks the EL84 wasn´t put in correctly or forced out at an angle. My immediate is to change the phenol base with either a ceramic or Belton hard plastic type. Then, use a defunct tube to widen the new socket jaws BEFORE the new tube is inserted. This will reduce any pin cracking.
Along with the old rule, DO NOT disconnect the o/p secondary under load or even with no load as circuit could oscillate.
BB
Along with the old rule, DO NOT disconnect the o/p secondary under load or even with no load as circuit could oscillate.
BB
For an over voltage condition use several diodes reversed biased from anode to ground. As mentioned try to use decent valve bases, like anything you have to shop around, probably not easy in your case living where you do. Lastly if this is a fault on one valve only it could be caused by a manufacturing fault, bad storage ( I've seen similar cracks in B9A valves stored in cold conditions whilst plugged into a socket) or induced stress whilst handling.
i made tube amp for 15 years .Thank you for your advice. This was an example of the cause of the spark. This happened to my friend in another city a week ago. The speaker wire was not disconnected. I had seen this many years ago and it happened again yesterday. buy . New tube is easy for you, but buying nos tube like Philips is not easy. It is different from buy ...jj.
no ....tube was not fault..... This is a serious ... danger in pushpull el84 circuits with maximum power .... the least mistake= damage
Making a simple spark gap. If your socket is like the picture... connect the middle rod to the ground. And bend pin 7 towards the ground. 2mm is enough. I tested this. The sparks never inside the tube .
The best protection is to use an RC circuit ar just a 330ohm resistor as a minimum load permanently across secondary
