Ion laser magnet connections?

[DMills]

Hi all,
As some of you know, I bought a mixed gas 909 off Jim with an OEM power supply (The one that resulted in the Halfnote disaster).

Now I seek the Ion laser gods advice....

Ok, Firstly this thing does NOT at present have a centre tapped filament transformer, instead it injects the cathode current at one end of the filament transformers secondary, is this as bad a thing as I suspect?

I am looking for a suitable centre tapped transformer, but the current is huge making this a specialist part (I might end up winding my own over a big toroid).

Secondly, this laser appears to have the magnet disconnected at the power supply end of the umbilical, are my schematics just in error, or should I rig the magnet across the raw 370V DC bus when the main power is on?

I am aware that some of the (Coherent?) designs put the magnet across the tube actually inside the head, but according to the wiring diagram in the documentation this is not the case for a 909.
I am thinking that wiring the magnet in might make for a useful increase in power output?

Regards, Dan.

[mixedgas]

One, some ALC/HGM will start without a magnet, but NO magnet is bad. Next up, PM me, I can probably get you a balanced cathode transformer. Running unbalenced is bad.

MOST alc magnets go across the tube, but some are in series. Would you please measure the magnet resistance.

Steve , who cant get on the net very easily, so it may take a while to reply.

[DMills]

Magnet is ~130 ohms, so say 2.5A if wired across the main rectifier bridge, clearly this is not a series magnet.

PM sent ref transformer.

Regards, Dan.

[mixedgas]

variac, rectifier bridge, some filter caps = variable magnetic field, optimize your color balence.

But get a magnet on that beast. I imagine somebody didnt get the tube voltage and color ratio they wanted with the magnet on, and took advantage of the fact that in the HGM manual is a chapter on testing the tube field vs no field. But it was NOT designed to run prolonged periods with no field.

600-1100 gauss are typical values for a argon magnet, KR is usually less, but how much less is up to the tube designer.

expect to see your red/yellow balance change with teh field, as well as some blue green ration changes(minor)

You KNOW what you must do.

Whatch for inrush when charging the filter caps, usually a 5-10 ohm resistor limits inrush and a relay shorts it out a few seconds after turn on.

Steve

[DMills]

Yea, already played the inrush trips the breaker game, contactor and resistor found, just need to do the wiring.

Current thinking is a variation on the packaged version of the supply circuit,
interlocks -> enable charging, aux supply and filament transformer (and magnet) -> 40 second delay (Let the cathode heat up) -> start button enabled and current limit bypass contractor engaged.

Variac on the magnet is a good plan, stick it on the power unit front panel right beside the tube current control. Given the inductance of the magnet, the caps can probably be fairly small as a little voltage ripple is unlikely to translate into much current ripple?

I don't suppose you have the real skinny on tube voltage do you (Remember mixed gas on this one, so will be a bit low anyway)? The ALC manual gives maximum current (30A), but no data on what the acceptable range of voltage drop is.

The OEM supply is annoying as it will not fit in my preferred 19" rack format without totally excessive rework (which I am not proposing to do, life is too short).

Regards, Dan.

[mixedgas]

Pm sent \

Steve