Electronics Newbie wants to design something simple, needs a bit of help

Thread Starter


Joined Aug 8, 2017
Hello All,

I am an audio nerd. They kind that plays vinyl records, has old school tube amplifiers, and has sunk enough money into a pair of speakers that could pay for a nice used car. My tube power amp and tube preamp both run on vacuum tubes, and both are of the older vintage, so they are not graced with modern conveniences such as an hour counter for the tube hours. Tubes need time to break in, and worse, they wear out after a certain number of hours, so an hour counter will be a very useful device to attach to the amps. As luck would have it, both of my amps need to be re-tubed soon, so I want to design and build a timer to count the hours when I connect the new tubes.

Sounds simple enough! So I looked at the McMaster Carr website and saw a simple, LCD hour counter that is triggered by voltage. My thought was to get a project box, cut a hole in the front for the timer, and a hole in the back for the power cord, and simply plug this device into the power conditioner the I use for the amplifiers. When I turn on the power conditioner to listen to music, the hours start counting. Problem solved!

However, when I started discussing this idea with other audio nerds on an audiophile forum that I belong to, others showed interest as well. I am toying with the idea of making a batch of these tube hour counters rather than just one for me, and that's when the design began to need a bit more complexity, which is why I am here seeking your advice.

Many amplifiers have a 12v trigger on them to turn on other devices when you turn on one device. I believe the connection termination used is usually a 1/8" headphone jack connector. One interested party asked if my soon to be designed tube hour timer could be activated that way, so when he turns on his tube amplifier, the counter starts counting hours. This seems like a more accurate approach than mine, though of course, my amps do not have 12v triggers.

So, I would like to design and build a device that can handle both functions. If one does not have a 12v trigger, they can plug the timing device with a household power cord into a power conditioner or power strip that also delivers power to the amplifiers. One must turn off the power strip of course, if they want to stop the timer. The other user has a 12v trigger on his amplifier, and wants to activate the tube hour counter by simply turning on the power on his amplifier.

This describes two modes of operation. Can you help me to understand how this should be designed?

Does the 12v trigger on an amplifier actually provide a constant stream of 12v power? Or is it just a little pulse that triggers another device?

Could I put a toggle switch in my tube hour counter device to engage or bypass a switch that encompasses the 12v trigger option? This way I can bypass the 12v trigger function in my setup, but someone else can engage the 12v trigger feature in his setup?

I am happy to receive any advice or help. Thank you!!!