How to improve safety Shock hazard National NC-98 Ham receiver and add standby switching

This receiver came to the shop for addition of standby switching and general checkout. Turned into a bit more than expected. A shock hazard was hidden, bit me. I planned to replace the power cord with a grounded type, but the little defect beat me to the punch!

[@sa8die]

Mr. Carlson would be very happy with this mod.

[@yardleybottles6025]

Thanks Terry! You are the rock and roll boatanchor Guru!

[@vtradio]

Terry, This morning, I touched the top of my newly recapped National NC-98, and it gave me a small bite (shock). It had been on all night in Stand-By, and I was in my bare feet. If I sat on a stool with my feet in the air, no shock. I just checked the voltages. From chassis ground to my fingers, 45 VAC. From chassis ground to the power stirp, 119 VAC! I did your transformer test, and it was good. This receiver was recently acquired by me in an estate sale. I was just testing the tubes before an alignment. I found two incorrect tubes (so far). I decided to ask Google if there was some mod I was not aware of. Your video came up first. I had forgotten that I commented on it two years ago (below). I'll be installing a 3-prong cord, just like I did on my Hallicrafters S-40B. Thank you. 73 Paul AA1SU

[@fredderf3207]

I have an NC-98 that I would like to have checked out, and realigned. When I was a kid, my grandmother was a solderer on an assembly line at National Radio in Melrose, Mass. She taught me how to solder when I was around ten or eleven years old. These radios were made about the time she was working there so I’ll never get rid of it, but I’d like to use it again. I also the same National Radio speaker that you have up on your shelf.

[@hestheMaster]

Safety first when checking out circuitry with household voltage. I always put in a grounded plug when restoring test equipment. Especially with a metal case, Heathkit ahem.

[@patrickwall8517]

That shock hazard is common with most receivers of that era. I have a Lafayette KT-320 and it had the same issue till I performed that mod. fortunately it did have a fuse, so I didn't have to add one.

[@sincerelyyours7538]

Well done, Terry. I plan to add a similar circuit to my Hammarlund HQ-120-X HF receiver and a much more modern SDR. Also, good job on the grounded power cord. Some of my radios are too small for a three-pronged cord so I use a two-pronged polarized plug and appropriate safety caps instead. Works well in countries that have polarized outlets but not three-pronged grounded outlets.

[@vtradio]

Terry, thanks for the tips. I keep getting zapped by my Hallicrafters, until I install a 3 prong cord.

[@russellhltn1396]

Big Clive observed that a lot of kids who got shocked ended up going into electrical vocations.

[@josephcote6120]

I got my start at about 3 yrs old. Straight for the outlet with keys on a metal bead chain.

[@sparksw9dkb187]

Muting is provided at pins 8 and 1 on the accessory socket. Extend lines to NC T/R relay contacts.

[@johnjohnson3221]

That death cap is spooky

[@johnsimms3957]

Excellent Terry! And very educational. You brought that receiver up to date.

[@lakerat3494]

I have one of these...thanks for the valueable info on it...repalcing cord now and gettining rid of cap...

[@rayislooking2]

Great Job Terry Love how it does not pop when you switch to standby. Thanks for sharing Just1

[@waynethompson8416]

Wondering why you decided not to use a "Safety Capacitor" in place of the "Death Cap"???

[@y_x2]

The problem with leakage is always there with a two prongs plug and a transformer. The voltage that you measure is due to that cap AND also the capacity of the transformer! Since that last one is smaller that the cap that you have removed you still see voltage BECAUSE you are using a high impedance voltmeter. It is not the voltage that kill or shock people but the CURRENT! Without that cap the current is very low you won't feel nothing. Of course using a three prongs plug kill that current.

[@mfbfreak]

This is true, the measurements don't give a good indication of the shock hazard. However, removing or replacing the cap, and grounding the chassis are both very good ideas. Those caps always fail, and relying on the transformer's isolation is also relying on one single factor of safety. Only one thing has to go wrong before the chassis goes live. With a ground connection, it takes 2 faults to make it dangerous - firstly the ground connection has to fail, and secondly something like the cap, the transformer, or a live wire coming loose. It doesn't happen often, but i've had a transformer go leaky, and also one case of a mains wire coming off. Without ground, in both cases a nasty voltage can appear on the chassis.

[@Thomasp671]

Hi Terry... Wanted to asked what size Voltage and Amperage fuse did you install ?

[@dragonlaker]

Great job. Superb !! Thank you for sharing.

[@preiter20]

Great safety tech tips Terry. What was the choice of "testing lubricant" in your glass?

[@ThePianoforever]

The mighty death cap!

BRAVO THERRY!!!! 👍👍👌

[@superhet7281]

Great job, Terry! Those blasted line bypass caps are always trouble. And it was only rated at 400V! One good spike could take it out. How did you determine the value of the fuse?

[@kornami8678]

Well done.

[@lakerat3494]

Hi D-Lab...I have a question about deoxit and fader lube to be used on the switches and pots. my main concern is the wafer switches. I see these have a carbon deposit on them. is it ok to use these products on this ? thank you.......

[@willrobbinson]

thank u well said at the end at end video , like minds :) ps great chassis no corrosion of copper , super

[@tomfinley6620]

So where's the plan for the added muting board. Or are you selling them Thanks.

[@FixitFrank]

Hello! Do you sell these standby modules/kits or do you have schematics available? I recently picked up one of these and just replaced the power cord with a grounded version as per your video.

[@d-labelectronics]

Yes, see d-labelectronics.com

[@rciancia]

Well done Terry. Question : When you changed the power cord, I noticed a brown wire flapping in the breeze right above the transformer ( Between the 2 green wires) . Any idea what this is ? maybe part of the output transformer ?? Very well done my friend

[@d-labelectronics]

Hi Ron, Good catch. Those are the 5VAC windings that should be connected to the 5Y3. The fellow had diode rect the radio. I have reversed that and the 5Y3 is reinstalled.

[@rciancia]

@@d-labelectronics I figured it was something like that but with DLAB on the case, it will always be perfect when its done !!!! Well done Terry

[@f.k.burnham8491]

RE: 3 wire grounded cords: If you don't fry, you don't die. Nuff sed.

[@Wizardofgosz]

Terry, is there no advantage to putting a Class Y safety cap to replace the death cap?

[@mfbfreak]

It's hit and miss. It does reduce mains noise slightly, but in my experience most interference enters via the antenna. For the 5 minutes and 1 euro it costs to put a fresh class Y cap in, i'd just put a new one in :)

[@hippyamp]

is there a reason for putting the fuse before the switch?

[@dhpbear2]

What was 'leaking' to cause that 30 volts?

[@d-labelectronics]

Stray Chassis AC

[@a1nelson]

D-lab Electronics I’m restoring my NC-98 right now. After enjoying looking at it on the shelf for about 25 years, I think I finally have the skill to tackle a quality restoration. I used it exactly once, immediately blew a cap and didn’t dare touch it until now. Maybe I’m too used to designing semiconductor electronics - I don’t really understand what you’re referring to. Could you elaborate just a tiny bit on what you mean by stray chassis AC, please? Love your channel, btw. Thanks.

[@PapasDino]

Nice Terry...if noise is a problem I guess you could install a Type Y safety cap in the "Death Cap's" place. TNX for sharing! 73 - Dino KLØS

[@hestheMaster]

Did that to a Heathkit C-3 Condenser Checker which is now safe to use.

[@timwilliams9443]

Looking to purchase a nc 98 for my youngest son.

[@josephcote6120]

This is just me, and I 99% work on my own gear: I like to put an input filter IEC jack to replace old line cords. If appropriate, I always suggest that to the people who bring me things to work on. For this radio you'd end up with better than original noise filtering. The jacks aren't too expensive, but I got a big supply of them by buying up a huge lot of broken computer power supplies. I fixed about half of them (bad caps) and made a decent profit be selling the fixed ones. The rest got scrapped for parts, and every one of them had that IEC filter jack.

[@user-ex3oe8gg2b]

Был.у.меня.Радиоприюмник.Казастан.в.металический.клрпус.блог.укаве.сбох.ата.рабочий.