Voltage control to Rodgers Drawknob lamps

[JoeyB3]

I'm working on this console that was originally a Rodgers and has since been converted to run Hauptwerk.

The console is currently using the DTS Midisystems encoding hardware (http://www.dtsmidisystems.com). The problem is, the company that did the conversion did not take into consideration that all those 12V bulbs stress out the ICs on the boards and as a result, I have burned one of them out (an IC, not a bulb). When I turned on the unit and turned on all the stops to test them (there were 8 burnt out lamps I replaced wired to this one board) the board, a DC-24, started to smoke.

In speaking with the owner/designer of the boards, he told me that if I could "lower the voltage to the lamps to 7 or 8 volts, that will reduce the over heating and over current issue."

Can anyone offer a suggestion as to how something like this could be done without replacing all those bulbs? There are 59 lighted drawknobs in total, and replacing a total of 19 burnt out ones over the weekend made me create new curse words. The thought of going in and doing all 59 is something I'm not even remotely interested in doing. Thanks...

[geoelectro]

You could "create" a new power supply for the lamps. Assuming all the lamps are connected commonly to the 12Vdc with the IC switches pulling the lamps to ground. You could put an 8Vdc regulator between the 12Vdc and the lamps. The main issue is a regulator strong enough wattage wise to supply all the lamps at one time. OR, A separate regulator per division would spread the load out. Then the regulators could be smaller, just more of them.

The cheapest was would be a 4 or 5V zener in series with the 12Vdc supply. That zener would need to be able to handle all the current or like mentioned before, use several to spread the load out. You could even consider varying the voltage for light dimming.

Geo

[JoeyB3]

Thanks, Geo...
It appears that 8Vdc regulators are inexpensive enough and would be easy to put in place. I'm thinking that should do the trick.

QUESTION: you are correct in that the IC pulls to ground. That being the case, do I get a Positive 8V regulator, or a Negative 8V regulator? Sorry for what I am sure is a stupid query!

Best,
Joey

[quantum]

Don't know if it would help or not, but some Rodgers models had a built in dimmer for the lighted knobs. For example, on the 760 it is located under the keydesk beside the headphone jack.

[JoeyB3]

Thanks, quantum.
I've ordered a pair of adjustable voltage regulators... as there are separate 12V feeds for each jamb. I'll dial it down to about 8VDC or so and I think I'll be fine.

Unless there is someone out there who knows of a suitable LED replacement lamp that operates in and around the 5V neighborhood?!? I have no desire to go in and swap out 59 bulbs, but I am pretty confident that all new LED lamps should outlast me in terms of life expectancy and I'll likely never have to replace one again.