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 Post subject: Meter rectifier in Heathkit TC-3 tube checker
PostPosted: Aug Fri 31, 2012 9:09 pm 
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I'm refurbishing this simple tube checker and see that it has a rather strange-looking (to me) meter rectifier. It's the thingy in the very center of the photo below which looks like a short stack of washers. I suspect it ought to be replaced with something like a 1N400X-series diode, but would like some expert opinions first.

Thanks!

Tom


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 Post subject: Re: Meter rectifier in Heathkit TC-3 tube checker
PostPosted: Aug Fri 31, 2012 9:38 pm 
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I think that is a copper oxide rectifier. Don't replace it unless it is bad. A 1N4000 rectifier won't work correctly.

BTW, it appears that you have at least two poor connections (unsoldered); one on a slide switch and one blue wire below the wiring harness. I would suggest carefully searching for any more.


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 Post subject: Re: Meter rectifier in Heathkit TC-3 tube checker
PostPosted: Sep Sat 01, 2012 1:38 am 
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Yes, I agree. Don't touch that rectifier but spend lots of time going over every soldered connection.


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 Post subject: Re: Meter rectifier in Heathkit TC-3 tube checker
PostPosted: Sep Sat 01, 2012 1:58 am 
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Thanks, gentlemen. I'll leave it in and hope it's still OK. I'm aware of the bad solder joints. That's what I was refering to in my OP when I said "refurbishing." There are many more than the few you can see -- I have to wonder if this thing ever worked from the git-go.

Tom


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 Post subject: Re: Meter rectifier in Heathkit TC-3 tube checker
PostPosted: Sep Sun 02, 2012 5:52 pm 
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I've got one too..........Thanks for the input!


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 Post subject: Re: Meter rectifier in Heathkit TC-3 tube checker
PostPosted: Nov Thu 23, 2017 4:25 pm 
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Replaced my rectifier in my TC-3. All done now! :D


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 Post subject: Re: Meter rectifier in Heathkit TC-3 tube checker
PostPosted: Nov Thu 23, 2017 5:24 pm 
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sea-bee wrote:
Replaced my rectifier in my TC-3. All done now! :D


what did you use?

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 Post subject: Re: Meter rectifier in Heathkit TC-3 tube checker
PostPosted: Nov Fri 24, 2017 2:52 am 
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If the line voltage voltage function is correct, you do not need to replace the meter rectifier. It does not power anything else in the tube tester.

Copper oxide rectifiers are extremely stable, which is why miniature ones were used in meter circuits. Heathkit used them in all their tube testers from the 1947 TC-1 until the 1967-era IT-17. If you leave them alone they will outlast every other part in the unit. Metallic rectifiers are different than other types in that they begin conducting as soon as the voltage across them is more than a few millivolts. No rectifier diode (1N4007 et al) comes close. If you do have to replace a copper oxide meter rectifier, a small signal detector diode like a 1N191 would be preferable. Some recalibration of the meter circuit will likely be needed.

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 Post subject: Re: Meter rectifier in Heathkit TC-3 tube checker
PostPosted: Nov Tue 28, 2017 2:42 am 
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I found a NOS one.


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 Post subject: Re: Meter rectifier in Heathkit TC-3 tube checker
PostPosted: Nov Tue 28, 2017 6:09 am 
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What happened to the old one, and where did you ever find a new one??

Dave


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 Post subject: Re: Meter rectifier in Heathkit TC-3 tube checker
PostPosted: Nov Tue 28, 2017 9:57 pm 
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Chris108 wrote:
Metallic rectifiers are different than other types in that they begin conducting as soon as the voltage across them is more than a few millivolts.



Seems like the low drop would make them ideal for a detector in a crystal radio? I don't recall this being discussed anywhere.

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 Post subject: Re: Meter rectifier in Heathkit TC-3 tube checker
PostPosted: Nov Tue 28, 2017 10:26 pm 
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Location: Mpls, Minnesota
Abstract:
A new type of radio detector has been developed which depends for its action on the rectifying properties of the boundary between copper and cuprous oxide formed on the copper at a high temperature. In order to make the copper-oxide rectifier useful up to broadcast frequencies, it was necessary to use small disks and a high current density. The high current density was obtained in part by connecting an inductance in parallel with the rectifier and tuning it with the rectifier capacity. The circuits developed possess unique advantages in that harmonic distortion is practically eliminated, a stage of audio-frequency amplification is eliminated, and automatic volume control of variable , μ tubes as well as other tubes is achieved without the necessity of using an auxiliary tube for volume control. A newform of automatic volume control made possible by the use of a single rectifier element as an asymmetrical resistance is described and discussed.
Published in: Proceedings of the Institute of Radio Engineers ( Volume: 20, Issue: 10, Oct. 1932 )


Here is information and a good article with pictures to make a detector.
http://www.hpfriedrichs.com/radioroom/c ... -diode.htm


Dave


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