Post by Steve on Jan 21, 2024 16:00:51 GMT 12
I think I have shown this before... but David (Trombone) was asking for the schematic a while back, and I finally found it today (I put it somewhere safe!). I also had to fix it (I showed this at our local club a while back and it didn't work - I just today figured out why). While fixing it, I drew out the schematic to see what on earth I built (it was a good few years ago)!
They do say that if it's stupid, but it works, then it's not stupid... but this is stupid because it's not all that safe. It does one job, it does it well(?!), and so I haven't made it 'better' other than to add new connectors for new magic eye types.
The transformer is just one that was laying about — a 5- or 6-valve Collier and Beale one from memory... I only needed HT and 6.3V, nothing special. The 100k and 68k resistors are to give around 250V on the red wire, which is the standard HT voltage needed by most eyes. The grid voltage is only roughly 0 to -4V (tapped off the 6.3V winding), but it's enough to prove the eye works so I'm ok with it. Other values were just what I had lying around and no real engineering or exhaustive testing was done... it worked, and so I stopped developing it. Could it be improved? Absolutely. I've actually got a high voltage booster power supply board for HT, and an LM317 (for the heater voltage), along with four 18650 batteries set aside to make a portable one so I can test them when I find them - but it's low down the to-do list. I've also considered building a case for this current one but again - the to-do list is long, and this works as it is.
Currently it can, on it's four sockets, test 6E5, 6U5, 6G5, EM34, EM35, EM80, EM81, EM84, EM85, and EM87 (and probably a few others that fit the pinout of those 4 groups). I need to add one more octal socket to test Y61, Y63 and 6U5G / 6G5G eyes, and a P-base socket for EM1's etc. But - I typically only need it to be able to test 6U5's (which is the predominant magic eye used in the sets I work on), the others are just handy.
So - here is a challenge: Make a better one... or a worse one... or a more awesomer one. Let's see what you can come up with to test magic eyes. Just make it about 647% more safeness than mine!
David, finally - here you go 🙂
Cheers, Steve
They do say that if it's stupid, but it works, then it's not stupid... but this is stupid because it's not all that safe. It does one job, it does it well(?!), and so I haven't made it 'better' other than to add new connectors for new magic eye types.
The transformer is just one that was laying about — a 5- or 6-valve Collier and Beale one from memory... I only needed HT and 6.3V, nothing special. The 100k and 68k resistors are to give around 250V on the red wire, which is the standard HT voltage needed by most eyes. The grid voltage is only roughly 0 to -4V (tapped off the 6.3V winding), but it's enough to prove the eye works so I'm ok with it. Other values were just what I had lying around and no real engineering or exhaustive testing was done... it worked, and so I stopped developing it. Could it be improved? Absolutely. I've actually got a high voltage booster power supply board for HT, and an LM317 (for the heater voltage), along with four 18650 batteries set aside to make a portable one so I can test them when I find them - but it's low down the to-do list. I've also considered building a case for this current one but again - the to-do list is long, and this works as it is.
Currently it can, on it's four sockets, test 6E5, 6U5, 6G5, EM34, EM35, EM80, EM81, EM84, EM85, and EM87 (and probably a few others that fit the pinout of those 4 groups). I need to add one more octal socket to test Y61, Y63 and 6U5G / 6G5G eyes, and a P-base socket for EM1's etc. But - I typically only need it to be able to test 6U5's (which is the predominant magic eye used in the sets I work on), the others are just handy.
So - here is a challenge: Make a better one... or a worse one... or a more awesomer one. Let's see what you can come up with to test magic eyes. Just make it about 647% more safeness than mine!
David, finally - here you go 🙂
Cheers, Steve
