Lektra TM-8 Timer Needs Help

Hello,
Well, I finally got my 8x10 Chromega enlarger moved in and all set up (quite a job). But, hooked up the big old Lektra TM-8 and the little red start button doesn't work. The enlarger lights up when I move the switch on the timer to the "focus" mode, but the little red button won't start the actual timing.
I need this timer because its rated at 1000-1500 watts, so another little timer won't do.

Does anybody know where to get a small "start" switch that I could use in this, a place to get it repaired or does anybody have a whole timer sitting around that they would like to part with?

If you got answers, I could use the help.

thanks,

Robert Newcomb

> hooked up the big old Lektra TM-8
> [to my] 8x10 Chromega enlarger
> and the little red start button doesn't work.
> I need [a timer] rated at 1000-1500 watts
> If you got answers, I could use the help.

Some of the Super/Chromega/I/II/III/whatever power supplies have a female receptacle in the back that connects to the timer. In this case the power supply contains a 15A contactor that controls the lamps in the head. If the receptacle is in the form of a 120V male plug then you can plug the power supply into the timer of your choice. If there is a ‘jones’ plug then it is meant to plug into a dedicated Omega timer - however things can be rewired to use any timer.

If you need a timer that can control 10A then you will need a contactor. Omega sells a contactor to control the enlarger for about $350. However, 10A contactors are not that expensive. The best contactor solution is a mercury plunger relay, a 60A unit can be had for about $50 - an example, picked out of the blue, is:

http://www.struthers-dunn.com/images/stories/pdf/CLASS MDR.pdf

These are available from most electric and electronic supply houses. If you know a ham radio operator or electronics tech they can help you wire it up, it needs to go in a UL approved enclosure and all that.

> does anybody have a whole timer sitting around
> that they would like to part with?

Funny you should mention ... I do happen to have a few f-Stop timers hanging about and that I wouldn’t mind parting with. They will, however, need a contactor to handle 10A - unless there is a ‘timer’ outlet on the back of the head’s power supply.

Thanks for the helpful input. I took the cover off of the power supply for the colorhead and it has no relays in it, which I think is what you are calling a contactor. So, it must need an external power relay that will handle 10 amps, or a timer that will directly handle 10 amps. This Lektra TM-8 is the only timer I know of that will take that kind of current. I'd prefer not to have to find and pay for the Omega power relay because they are expensive and the large Omega parts & pieces are getting hard to find as well.
I may try and wire up a relay using parts as you talk about above.
One thing I did learn. This old timer actually has vacuum tubes in it. Once I looked at it carefully and thought about the old ways of tubes, I relized that maybe because of the tubes, the timer needs to warm up before using. Sure enough, let it warm up for 10 minutes and it times just fine.
Since it is so old, with tubes and heavy electrial contacts etc. I plan to try and come up with some other alternative when I get the chance.

thanks for the help,
Robert Newcomb

> This old [Lektra TM-8] timer actually has vacuum tubes in it.

That certainly qualifies for being -analog-. If it works, what the heck. But as you mention, reliability isn't going to be that good. It must be ~50 years old and most of its parts and peices are going to be approaching end-of-life. Tube equipment runs hot and that shortens the life of the capacitors, resistors and such that are in the unit. Not to mention the low reliability of vacuum tubes themselves. Some vacuum tubes are still made as there is a market for them in esoteric audio equipment.

> I took the cover off of the power supply for the colorhead and it has no
> relays in it, which I think is what you are calling a contactor.

A contactor is much like a heavy-duty relay meant for high current and high voltage. The design of a contactor is often different from a relay, and a contactor may have blow-out magnets and baffles to quench any arcs from current interuption. Most are dry contact. Contactors for really reliable operation, such as in street lights, use a sealed tube with mercury and a plunger that is pulled into the mercury with a coil around the tube. You can get small [10-15A is small for a contactor] dry contact units for $10-20. McMaster Carr http://www.mcmaster.com/ is a good source, but HomeDepot & Co. also carry the beasts.

The Omega power supply may use SCR's or Triacs to turn the lamp on and off. If there is a plug marked 'timer' then the chances are the power supply has an internal method for controling the lamps.

If you need to add a contactor to the system see if you can mount it inside the Omega power supply chassis - that will keep the number of electrical cords down and you won't have to supply a NEMA box to hold the contactor.