Help with SP125 HeNe

[Laserhobbit]

All,

I have been moving my workshop this weekend and lurking at the back was a vintage 1960's SP125 HeNe and SP 250 power supply/exciter. The tube was regassed in 2002 and since then it has only run for a few hours. yes I know all of you vintage HeNe collectors will be snarling at my lack of respect for such an instrument, but a divorce, a wedding and a few funerals ( could be a good idea for a film ) ) meant it was left far too long. Fired it up this morning and the good news is a great salmon pink glow. It has gone out of alignment, no surprise and so far I only seen the slight blue glow of the end discharge. But now I need some help. Does anyone have a manual for both the head and exciter? It has been about ten years since I set it up and I am not sure about the alignment method, I don't want to stress the tube by doing it wrong . Also I have lost the RF lead, I have ordered a new one and so can test this later in the week. Does anyone know what the RF does and how important it is? The reason I ask is that the meter showing RF current reads zero whatever the setting. It may just be because there is no load, but I wonder if one of the RF bits has failed. anyone else any experience of this exciter and head?

We have a UKLEM next weekend and I would really like to take this along to show a few people what a really great HeNe could do. so any ideas and where I can find the manuals would be really appreciated.

Thanks

Steve

[mixedgas]

I have the manual.

The RF bit is really important for getting stable power.

I'll take the manual with me when I fly tomorrow, I can scan in what you need on the road, if your specific about it.

Alignment is a #itch, so assume its close to aligned and not having the RF may be a issue.

Steve

[mixedgas]

see attached procedure, manual says you can ignore RF for now.

Steve

[Laserhobbit]

Steve,

As usual you have come up trumps ) Thanks so much for your help. I will not get any time until the weekend to try this adjustment, as I am travelling also, if you think any other pages may be of help or have the schematic for the 250 exciter that would really be appreciated.

Kind Regards

Steve

[142laser]

I have never disagreed with Steve before but the RF is not needed for stable power and it kills the tube much faster. Don't run the RF without a proper cable for impedance matching or you may bkow the RF driver. I would run at 35 mA DC and no RF. You will get longer coherence length and better TEM 00 beam mode with the RF off and it only adds a few mW usually; see manual. It does cut down on 125 KHz noise but for holography who cares? You should also be able to get 10-15 mW orange at 611.8 by tuning thre prism... I have had two of these lasers-dead now. Phil Bergeron, USF Physics

[142laser]

Oh yeah and cleaning and alignment IS a bitch; Steve is dead right about that. It the tube is OK the RF only adds a little power and causes some non TEM 00 modes to lase (you can see the beam diameter get bigger). RF causes faster loss of Helium; that os one of the main reasons it was dropped for DC. The laser does not need RF to lase. Best wishes, Phil

[dnar]

It's great to see the resources, knowledge and helpfulness here. What a group.

[142laser]

I am glad to offer my experience to help get old lasers running. I am in with Sam Goldwasser who owns Sam's Laser FAQ and we have MANNY old Spectra Physics lasers that still work...130, 132, 133P, 135, 127 etc. My 125A's died or are close to dead; cathode failure. The RF is mainly for noise suppression and is not needed for lasing.
Phil