This device has a power transformer with the mains connected to the primary. What you are measuring is the leakage through the transformer capacitance to chassis. There is always that leakage when you don’t have an earth wire on your power cord.
You are right about stray voltage caused by capacitive coupling. Especially since this transformer seems to have primary and secondary wound on top of each other. Using two separate bobbins for primary and secondary would have been preferred not only to reduce the coupling but also reduce the chance of crept in moisture causing leakage. And given the overall corrosion seen even in the inside I sure would also count in moisture effects.
Replace R14 on the "noise" voltage injection path with a new metal film of at least 2W - not for power dissipation but voltage rating reasons. Preferrably also use a higher value than 68k. Maybe 120k because while on page 20 of the manual it proudly states that in a tip to gnd short no more than 1 mil would flow, 114V/68k definitely passes more than 1mA on a tip to gnd short. And second modification you may think of is putting a high efficiency low current LED in series with R14 and mount it underneath the noise switch. Modern LED esp the low current cold white ones start to dimly glow at currents in the tens of uA range. If you used the "noise" function across a DC blocking cap it could give you a good indication of its leakyness even if the test voltage was just 114V.
I just recently reworked one of these myself - the front plate was bent in several places, so I had to remove all the components from it so I could hammer it flat. Also replaced the connection to the probe with a BNC connector, along with a mating BNC connector on the probe cord. IIRC, the rectifier diode was bad, so I just replaced it with a 1N4007 silicon diode, along with replacing the electrolytics and paper caps. Nice to hear you saved one from the trash, if for no other reason than to save an eye tube - those are getting pricey.
Cool beans, Jim! Glad you were able to get your shot despite the side effects. I'm due to get my first shot this Thursday, not sure whether it will be like yours or the Moderna one. Either way I'm ready.
@@stevec5000 Why would you voluntarily stay unvaccinated against something known to have killed over 2.7 million people world wide? I personally knew 5 folks who have died from it, two of whom lived less than a mile down the road from me and were a friend I went to school with and his Mother who died within 24 hours of each other from it. Yeah, thanks, but I'll take my chances with the vaccine that millions have already taken before me. Had my first dose earlier today at 1:50pm and don't even have a sore spot on my arm from the injection like I get when I get a tetanus shot or a flu shot.
IT-11 is a capacitor leakage tester, same design as the IT-28... the IT-12 is a signal tracer, and doesn't bring anywhere near as much on auction sites.
@@drtidrow - Yeah IT-11 and -28 are ridiculously OP on eBay. CZcamsr hype I guess... it's kind of silly really 'cause any cap (eg. waxies) one wants to test at any HV (for leakage) is a cap that should probably be tossed out and replaced anyway as it is (long past!) EOL. Cheers,
@@EngineeringVignettes Yeah, apparently the classic guitar amp crowd likes to use the IT-11/28 to reform electrolytic caps on old amps, as you can leave the voltage on for long periods of time - the leakage test switch doesn't have a spring return like many other testers of the time, (supposedly) allowing an electrolytic to reform its insulating layer. I don't trust that method, and just replace old electrolytic and paper caps with modern equivalents.
Ha, I think I got you beat on the losses there. Two Sencore LC53 units up on Ebay with the first I was outbid by $150.00. That went for $280!!! The second I was outbid by $1. It went for $185.50. Ouch!!! Not going to pay over $185 plus shipping and they still needed to be worked on.
There is a problem with the Astrazeneca has a problem and can cause clots but I suspect the doctors are aware of this but I hope that the problem doesn't happen.
Someone threw this out?🗑 Has a good eye tube. Leaky caps expected. Bridge rectifier replacing the single diode should be done. Wait, what am I talking about. Jim would never do that!
29:04 why do you rant that it is odd that the 12ax7 does not light up? At 23:30 and following you can clearly see the bad state the tube pins are in. They are anything but bare metal. This and given the overall state of the IT-12 must surely ring a bell and scream PROPER CONTACT CLEANING. It is amazing how truely simple observations and deductions always end in quarter hour lamentos.
This was such a simple set to clean up and properly fix up but somehow Jim dropped the ball. $10 worth of caps and a diode and that would have pretty much ensured this set to run many more years. Check the resistors to see if any out of spec and maybe even properly clean the contacts and an in-line fuse in it and put either a 3 prong or polarized plug on it and you wouldn't have to worry about getting your socks blown off every time you plug it in (or spend half a video measuring to see if there is any voltage on the chassis). Respect the AC hook up but don't worry yourself to death over it.
One nice thing about Heathkits is the excellent documentation for them - IMHO, they had the best build instructions of any of the kit vendors.
This device has a power transformer with the mains connected to the primary. What you are measuring is the leakage through the transformer capacitance to chassis. There is always that leakage when you don’t have an earth wire on your power cord.
You are right about stray voltage caused by capacitive coupling. Especially since this transformer seems to have primary and secondary wound on top of each other. Using two separate bobbins for primary and secondary would have been preferred not only to reduce the coupling but also reduce the chance of crept in moisture causing leakage. And given the overall corrosion seen even in the inside I sure would also count in moisture effects.
Thank you for your time and sharing Jim! Fun stuff. Make it look good! Joel
Replace R14 on the "noise" voltage injection path with a new metal film of at least 2W - not for power dissipation but voltage rating reasons. Preferrably also use a higher value than 68k. Maybe 120k because while on page 20 of the manual it proudly states that in a tip to gnd short no more than 1 mil would flow, 114V/68k definitely passes more than 1mA on a tip to gnd short.
And second modification you may think of is putting a high efficiency low current LED in series with R14 and mount it underneath the noise switch. Modern LED esp the low current cold white ones start to dimly glow at currents in the tens of uA range. If you used the "noise" function across a DC blocking cap it could give you a good indication of its leakyness even if the test voltage was just 114V.
Jim, one of your lights is causing pretty bad buzz. It stopped when you shut the lights off.
I just recently reworked one of these myself - the front plate was bent in several places, so I had to remove all the components from it so I could hammer it flat. Also replaced the connection to the probe with a BNC connector, along with a mating BNC connector on the probe cord. IIRC, the rectifier diode was bad, so I just replaced it with a 1N4007 silicon diode, along with replacing the electrolytics and paper caps.
Nice to hear you saved one from the trash, if for no other reason than to save an eye tube - those are getting pricey.
On the cap,
28-65 (or whatever the first number was) could be the week and year of manufacture, eg. 28th week of 1965.
Cheers,
I’ve watched a number of your videos, and enjoy them. Except when the camera is moving, have to skip those parts or I get a headache.
The RF signal must be modulated in order for you to hear anything in the RF signal. Merely sweeping frequencies does not mean the signal is modulated.
Cool beans, Jim! Glad you were able to get your shot despite the side effects. I'm due to get my first shot this Thursday, not sure whether it will be like yours or the Moderna one. Either way I'm ready.
Why would you want to be the guinea pig for something that is untested and potentially dangerous?
@@stevec5000 Why would you voluntarily stay unvaccinated against something known to have killed over 2.7 million people world wide? I personally knew 5 folks who have died from it, two of whom lived less than a mile down the road from me and were a friend I went to school with and his Mother who died within 24 hours of each other from it. Yeah, thanks, but I'll take my chances with the vaccine that millions have already taken before me. Had my first dose earlier today at 1:50pm and don't even have a sore spot on my arm from the injection like I get when I get a tetanus shot or a flu shot.
I got the Moderna one, Jim. No side effects for me at all....not even a sore spot at the injection site on my arm.
@@Rebel9668 Aren't you worried about what the long term effects might be?
This is an example of how to make a big issue for over and hour for something that doesn’t exist.
But it is entertaining even with all the silliness .
Man jim you are lucky. I just got outbid on ebay for an it-11 for over 100 dollars.
IT-11 is a capacitor leakage tester, same design as the IT-28... the IT-12 is a signal tracer, and doesn't bring anywhere near as much on auction sites.
@@drtidrow - Yeah IT-11 and -28 are ridiculously OP on eBay. CZcamsr hype I guess...
it's kind of silly really 'cause any cap (eg. waxies) one wants to test at any HV (for leakage) is a cap that should probably be tossed out and replaced anyway as it is (long past!) EOL.
Cheers,
@@EngineeringVignettes Yeah, apparently the classic guitar amp crowd likes to use the IT-11/28 to reform electrolytic caps on old amps, as you can leave the voltage on for long periods of time - the leakage test switch doesn't have a spring return like many other testers of the time, (supposedly) allowing an electrolytic to reform its insulating layer. I don't trust that method, and just replace old electrolytic and paper caps with modern equivalents.
Ha, I think I got you beat on the losses there. Two Sencore LC53 units up on Ebay with the first I was outbid by $150.00. That went for $280!!!
The second I was outbid by $1. It went for $185.50. Ouch!!! Not going to pay over $185 plus shipping and they still needed to be worked on.
Meant it-12
There is a problem with the Astrazeneca has a problem and can cause clots but I suspect the doctors are aware of this but I hope that the problem doesn't happen.
Jim : It's working 100%
(Insert audio clip of Consuela) No, No, No, No...
looks like it is fully working ./ to hear anything on RF you need a modulated signal.
Someone threw this out?🗑 Has a good eye tube. Leaky caps expected. Bridge rectifier replacing the single diode should be done.
Wait, what am I talking about. Jim would never do that!
29:04 why do you rant that it is odd that the 12ax7 does not light up? At 23:30 and following you can clearly see the bad state the tube pins are in. They are anything but bare metal. This and given the overall state of the IT-12 must surely ring a bell and scream PROPER CONTACT CLEANING. It is amazing how truely simple observations and deductions always end in quarter hour lamentos.
This was such a simple set to clean up and properly fix up but somehow Jim dropped the ball. $10 worth of caps and a diode and that would have pretty much ensured this set to run many more years. Check the resistors to see if any out of spec and maybe even properly clean the contacts and an in-line fuse in it and put either a 3 prong or polarized plug on it and you wouldn't have to worry about getting your socks blown off every time you plug it in (or spend half a video measuring to see if there is any voltage on the chassis). Respect the AC hook up but don't worry yourself to death over it.