Reviving a HeCd 4050

[daedal]

Moved from the FLEM thread to minimize thread clutter.

Hope you guys are having fun!!

Someone said there is a HeCd laser there that isn't lasing... if is a liconix head and you guys want to get it working I have some *very* hard-to-find info detailing how to change the Cd pressure and how to test what the Cd heater is set to, as well as how to test the tube voltage and how to see the actual cadmium temp. I'll post the info if you folks need it

I actually had 2 HeCd heads there... and that info will come in VERY handy, please!

Thank you loads!

--DDL

Edit:
If this helps any:
The big head is a 4050 split tube with 2 supplies and has some crazy "feedback processor" that seems to be the only tube's fault. It has an RF output that drives what appears to be an AOM of some sort, but when plugged in the unit flashes 'open loop' repeatedly regardless of wire being connected or not. There is an abundance of RF though as it constantly interfered with the audio system while switched on.
There also is another smaller tube (almost exactly half the big guy) that won't light. Should I zap it with a HeNe Supply a few times?
Thanx;
DDL

This applies to the dual discharge 4240N head, as well as the smaller "4xxx" series. I'm not sure about that 4050, though. That sounds weird. My supply has the 'rf style' connectors but its just HV going through them.

All these refer to the card inside the head. here's the info I have:

The loop wire is the common. Where it says "TP 4-6" it means test the voltage between test points (the little poles sticking out of the PCB with eyelet holes on top) 4 and 6.
TP1 - Com: Tube Voltage, this can be 6 - 7.5V, optimum is 6.5V. As the Cd level is increased the tube voltage will go down to a certain level.
TP4 - 5: Cadmium heater set point, .8 - 1.2/1.3V make slow adjustments to this and monitor the power this is what you want to use for optimum power.
TP4 - 6: is the actual Cd temperature, this trails the cadmium set point (TP4 - 5) by no more than .1V. (but make sure the head is warmed up and stabilized first)
The Cadmium set pot is the one between TP5 - 6 near the bottom right component side

My head was happy with a cadmium heater set point of .87V. The more you turn the pot clockwise, the lower the voltage will be. BUT I think lower voltage reading equals a higher cd heater temp, but I could be wrong.

Good luck! Maybe snap some pictures of that 4050. I wouldn't think the aom would have anything to do with an error in the PSU but then again I dont really know anything about that setup. Make sure the He heater and Cd heaters are plugged in, that's about all I can think of. Does the tube even try to start? Does the PSU have a 'remote' plug in the back that requires a jumper to defeat an interlock?

As far as getting hard to start tubes to light, you can use an oudin coil but I would be very careful. After doing this I had a supply fail, but it could have just been complete coincidence. Just turn it down to super low voltage and zap the tube halfway between the anode and cathode.

Thank you very much for the reply. Here are some pictures showing my tube in operation. If anything else is needed please let me know. I will also add the pictures of the smaller tube later on. The second one does not turn on at all. The supply seems to try and flash (sparks oddly visible in the ballast), but it will not ionize.

http://www.photonlexicon.com/forums/...php?albumid=86

Thank you;
DDL

try removing the covers from the ballast resistors. If the tube is a bit high pressure it will arc over to the covers, which can be really hard on the PSU. My head was doing this when I first got it, but after about 35 hours of runtime it is back to normal. Starts up instantly!

As far as the pictures go, it looks like you're vaporizing too much cadmium. It could be that the cadmium temperature sensor is not working or became disconnected somehow, giving you the 'open loop' light. Also, this would cause the Cd heater to just keep getting hotter and hotter because the feedback sensor see's that the cadmium is not up to the expected temperature. That's just a hunch. That is a neat setup though! What year is it? The tube looks identical to mine except I think that big thing on the OC end of your head may be an AOM or something... mine doesn't have that, and it looks like your cadmium reservoir is sideways whereas mine is vertical. Also, my psu is just one unit rather than the three separate units. Another thing to think about, although I'm sure you've made sure everything is in the right spot, is that those little gray connectors are what control the systems in the head (cd pressure, tube voltage, He heater, etc etc). Is it possible that some of them have been mixed up? It looks like you have about 4 different grey connectors there. Does only one come from the head?

It could also be that the head needs more helium, but this is rarely the case as the He reservoir leaks a tiny bit in storage, usually causing a bit too much He pressure. Is the He heater plugged in?

Thank you very much for the reply.

When we had this plugged in at FLEM the tube kept getting hotter, but I don't know what too hot is like, and neither of us did, so we kept it going. I'm not sure about the connections, but there is only one gray connector from the head, the one connected to the front of the second PSU. There are also 2 HV wires and they are connected as shown. The front of the tube has a light feedback sensor, which seems similar to my Ar head. Probably a piece of glass and some photo-sensor to tell the Feedback Processor how much light is actually being emitted. Based on this, I assume the RF supply control the output. This is based on the 0-100 dial and the available "External Modulation".

The tube starts right away though. There are no issues with the start-up, and the tube goes through all the regular steps as described in the Laser FAQ.

Thanx again;
DDL

[GooeyGus]

One other thing I've thought of.... have you seen those liconix laser stabilization units on ebay? It looks like it would work with your laser, it might be worth a shot!

Oh, and try to snap some pics of the control card in the head of your laser, I'm curious to see if it is the same card. If it is, you'll probably be able to get away with buying a 4240PS power supply and run it off that, rather than using 3 different units.

[daedal]

I'll take some more pictures of the control card tonight, but I did look at the stabilization units on ebay (great price) but they are not fit for my unit. The feedback from the sensor is different...

Thank you very much for the help.

Regards;
DDL

[dxs]

That's quite valuable information, many thanks!
How did you solve your PS problem, GooeyGus?

[daedal]

I agree.

Thank you again for the info GooeyGus.

I just got off a call with Steve and ended up taking some pictures of the AOM. Those are now in my album if anyone is interested in taking a look.

Will post some pictures of the board once I figure out what's keeping this AOM from going back into the hole!

Regards;
DDL

[mixedgas]

I spend some time on the phone with Daedal and reviewed the pics....

Ok, using the AO internally in the cavity AS THE DAMN TUNING PRISM is great if your a master optics technician with a support staff, but lousy if your trying to get to work 15-20 years later.

So first up,
He needs to make a new optics mount. Its also frequency and RF amplitude dependent as the cavity heats up.... Bad if your not the guy who designed it and know where the operating points are, so Daedal is a disadvantage here till the AO drops out of the picture.

Second of all his hecad tubes are self heating, so there is a operating point maybe 6-10 mA wide, so he needs to find the sweet spot for peak gain.

Third, hes got a dual, possible triple line system, so you guys could have had line competition while aligning, or a flash of the UV line and not known it.

I have told him about a fellow who lives near by who may know what to do.
Details l8tr to respect that persons probable desire for privacy.
Hint, for those in the know, he invented CW metal vapor lasers and teaches in Orlando.

Steve

[daedal]

I spend some time on the phone with Daedal and reviewed the pics....

Ok, using the AO internally in the cavity AS THE DAMN TUNING PRISM is great if your a master optics technician with a support staff, but lousy if your trying to get to work 15-20 years later.

So first up,
He needs to make a new optics mount. Its also frequency and RF amplitude dependent as the cavity heats up.... Bad if your not the guy who designed it and know where the operating points are, so Daedal is a disadvantage here till the AO drops out of the picture.

Second of all his hecad tubes are self heating, so there is a operating point maybe 6-10 mA wide, so he needs to find the sweet spot for peak gain.

Third, hes got a dual, possible triple line system, so you guys could have had line competition while aligning, or a flash of the UV line and not known it.

I have told him about a fellow who lives near by who may know what to do.
Details l8tr to respect that persons probable desire for privacy.
Hint, for those in the know, he invented CW metal vapor lasers and teaches in Orlando.

Steve

That last tidbit made flip off my chair when I first heard it...

Apparently, said gentleman is a couple minutes from where I am...

Nonetheless, Steve, thank you very much! Your help is truly priceless.

I have put the system aside for now while I try to get in touch with better knowledgeable parties. I believe the system is A-OK, but it just needs a new RF box. Somehow the one here has forgotten what it's supposed to do...

Hopefully there is light at the end of the tunnel

--DDL