lexel 85 strange noise in the head

[genesis]

Hi there
i post this message because i need some help about strange things.
last week we break a brewster window of our lexel 85 head (we not know how ^ ^).
to repair the resonator we change it with another one.
this tube was from a box and "sleep" since 10 years.
.
at the fisrt start the discharge won't start.

after some times with cathode on the discharge go on and the tube current go to 16A.
the passbank voltage is over 50v (out of the green scale) but not to high to kill them.

but after 20 to 30 secondes a strange noise appear from the start transformer. and the discharge stops.


we decide to let the cathode filament on for one hour to let the gas come from the reservoir.

after this the laser work for more time (about 1 minute) and the noise appear again and stop the tube.

now the tube voltage is near 124v @15A (i know this is too low) and when we try to increase the current to 17A the tube stop with same noise.

someone know this phenomen? we made a video and i think to post it here ASAP.

this is strange because the noise is similar of a start high voltage discharge and we kill two voltmeter (tube voltage) when the phenomen appear.

but we not notice blink of the discharge when this noise appear.

have you ever seen this thing on gas laser?

here is the video
http://fr.youtube.com/watch?v=L_m3UvMhbqw

[Dr. Burne]

Hi,

could be a high frequency ozillation of the tube current.

How do you replace a brewster window without gas refill? Be faster than 4.5 microseconds

I think this tube is dead and a old lexel85 OEM Tube is nearly nothing worth today


Regards Stefan

[genesis]

thanks for your reply.

i think to repair the broken tube and perhaps with some hour of working on this tube it can work fine again.

the oem lexel tube is hard to find. but work great (when he work )
today i try to connect another spare head with an unbilical cord to the power unit to see if she work well (but i'm pretty sure because this PSU work fine with the older broked head)