Hello my fellow Carlsonians! I recently purchased a TO-5 in very good condition. The unit is working, but the indicator tube is beginning to fade, and the components are all original. I will be slowly restoring this unit to its original glory and posting my progress along the way. If anyone has had experience restoring this or similar units I’m open for advice and suggestions. I’m new to tube gear and reading schematics so I won’t be offended by any advice however elementary. I do have a manual/schematic.
All too common on indicator tubes. I was using my Heathkit IT-28 one night (which already has a not so bright tube) and left it turned on by accident. Several days later I happened to notice a green circle much dimmer than before unfortunately. I do have replacements, but no point in putting a new one in to dim out, I just shield the light off the tube and go on with my testing. So word of advice, don’t leave them powered up for days at a time!
The rest as you know is pretty textbook. Safety first, take your time, pay attention, and enjoy the journey!
Radios + Tubes + Scopes + Cars= Nothing better!
@radtekman Hi, now that you had mentioned the happening I am thinking: maybe is worth a little effort of creating a small timer board (AKA: magic eye saver project 🙂 ) with the use of…a let,s say a tiny SMD style 555 timer IC and a small size Power Mos-Fet and make it work as following: When you switch on the IT-28 for the first time the magic eye stays OFF by default but the minute you try to use the instrument you-ll push a spring action push switch (that is mounted somewhere in the vicinity of the magic eye or at the rear panel) and once pushed a preset 10-15 minutes timer will start counting and when the time is up a small size power Mos-Fet will interrupt one leg of the 6.3V AC magic eye’s filament and in turn interrupting the electrons emission saving the tubes life considerably. Another option would be to use a little latched relay (instead of the Mos-Fet) so 1 pulse will turn the relay ON and another pulse will turn it off again. The whole board can be fed directly of of the 6.3V AC (rectifier + filter = about 7-9V DC) . But then again, the IT-28’s architecture needs to be analyses first to see what are the real options My idea is a pure wild guess at this very point as I never had and IT-28 before nor am I familiar with its architecture. My 2 cent 🙂
PS: I am having a second thought @ my idea:
and perhaps interrupting the filament is not the greatest idea because when resetting the timer you will then have to wait a fair bit of time (15-20 seconds) until the tube warms up a properly to allow for a great emission. so…a much better idea is to interrupt the B+ of the magic eye by using a small size and properly voltage rated REED relay or an appropriate Mos-Fet and perhaps a P Chanel one such as the one MCL employed for the curve tracer’s CRT saver circuit/project.a small size power Mos-Fet will interrupt one leg of the 6.3V AC magic eye’s filament and in turn interrupting the electrons emission saving the tubes life considerably