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 Post subject: Heathkit v-7a DC Probe
PostPosted: Sep Sat 11, 2021 12:28 am 
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Joined: Aug Wed 04, 2021 3:43 pm
Posts: 124
Hi guy's,
Is there anything special about the phono plug used in the v-7a?

I'm going to fabricate a probe and want to know what's ahead before I start.

I need:
Phono plug
1 meg ohm resistor
Shielded cable
Probe handle and tip capable of housing the resistor.

Any thoughts, advice, recommendations or suppliers would be greatly appreciated as well as photos of your probe.
Thank you in advance for you help and support.
Robb

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 Post subject: Re: Heathkit v-7a DC Probe
PostPosted: Sep Sat 11, 2021 1:47 am 
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Joined: Mar Sat 14, 2009 5:56 pm
Posts: 4626
Location: VA 22602
Very easily constructed.

Phono plug is very common
1 Meg resistor is very common
Coax – use RG-174, flexible and thin
Probe, a common VOM, VTVM probe is large enough to contain a resistor and accept RG-174 coax.
I could pull those parts out of my piles in a few minutes as many here would be able to do.

Post your location and you may be able to get the parts locally.
If you lived near me I would give you the parts.

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 Post subject: Re: Heathkit v-7a DC Probe
PostPosted: Sep Sat 11, 2021 1:58 am 
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Joined: May Thu 14, 2015 4:15 pm
Posts: 3515
Location: Dallas, TX
I think the proper name for that connector is "phone" not "phono".
Phone as in headphone, in this case 1/4 inch. At least two miniature versions are also available now, as well as stereo versions.
Phono as in phonograph, is also called a RCA connector, always monophonic (single channel).

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Tim
It's not the Destination, It's the Journey.


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 Post subject: Re: Heathkit v-7a DC Probe
PostPosted: Sep Sat 11, 2021 2:35 am 
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Joined: Jun Sat 15, 2019 7:43 pm
Posts: 1469
To answer your question, yes the plugs were special to handle the voltage.
https://antiqueradios.com/forums/viewto ... 8&t=354325

You can download the manual here, instructions are in it on how to construct the cables.
https://www.rsp-italy.it/Electronics/Ki ... Manual.pdf

As the original heathkit special phone plugs are no longer available many people just use a regular phone plug, you wouldn't want to be testing high voltage with this tester anyway.

DM


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 Post subject: Re: Heathkit v-7a DC Probe
PostPosted: Sep Sat 11, 2021 5:39 am 
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Joined: Mar Sun 20, 2016 11:04 pm
Posts: 1117
Location: Mesa, AZ 85206
These ar excellent...and are rated for 1.5kV.

https://www.tubesandmore.com/products/1 ... ian-series

steve


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 Post subject: Re: Heathkit v-7a DC Probe
PostPosted: Sep Sat 11, 2021 5:47 am 
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Joined: Jan Tue 10, 2012 8:39 am
Posts: 2820
The data sheet shows no voltage rating. Maybe I missed it.


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 Post subject: Re: Heathkit v-7a DC Probe
PostPosted: Sep Sat 11, 2021 6:28 am 
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Joined: Aug Wed 04, 2021 3:43 pm
Posts: 124
Sorry about the phono/phone mistake....these predate me. I'm in Palm Bay, FL if anyone is local or knows a supplier. I'm headed to a swap meet tomorrow or Sunday to see what I might find. We also have a local shop called MRAM. They buy surplus and part it up. I may start my Saturday there as our swap meet isn't that great. BTW: It came with a manual so I've been reading and rereading it. Also I will check out the link provided as I have no stockpile yet. I'm sure in the near future I will lol.

I have some issues with this meter that I need to work on. It has the 150v capacitor that I will replace as well as the original selenium rectifier. My pointer was bouncing all over creation when I powered it up today. I left it on for a few hours and when I returned I had nothing on any scale or selection for the switches.

Question:
What diode should I replace the rectifier with?
Simply switch from a 150v cap to a 250v 16 microfarad?

Thanks again to all.
Robb

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 Post subject: Re: Heathkit v-7a DC Probe
PostPosted: Sep Sat 11, 2021 6:38 am 
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Joined: Aug Wed 04, 2021 3:43 pm
Posts: 124
bob91343 wrote:
The data sheet shows no voltage rating. Maybe I missed it.


Attachment:
Screenshot_20210911-013634_Chrome.jpg
Screenshot_20210911-013634_Chrome.jpg [ 220.06 KiB | Viewed 467 times ]


These are interesting. Thanks for posting them as an option.
Robb

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 Post subject: Re: Heathkit v-7a DC Probe
PostPosted: Sep Sat 11, 2021 3:26 pm 
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Joined: May Thu 14, 2015 4:15 pm
Posts: 3515
Location: Dallas, TX
One of the smart things to do in this business is to order everything from one source to reduce shipping costs.
Antique Electronic Supply isn't the most inexpensive source for parts but if they have something other places don't have it may be worth it.
1N4007 rectifier diodes are used for may power supply applications, they can handle an ampere and as much as 1000V. Inexpensive 25 cents, get 10 or 12.
I found a 22uF 160V capacitor that will do, 200V would be optimum but they don't have any that are too much capacitance or too much voltage (you wouldn't want 400V). A little more capacitance than the original won't hurt in a power supply, a bit more voltage is a good idea but you shouldn't go too far.
There are much more affordable places to get tubes, but if you really want to up the total they have the 12AU7 tubes. Audio equipment uses 12AU7 tubes often, so they are in demand so $$$.
Switches in old electronics often get corroded or dirty and cause random operation. Cleaning switches and controls is always something to put on your list of things to do.

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It's not the Destination, It's the Journey.


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 Post subject: Re: Heathkit v-7a DC Probe
PostPosted: Sep Sun 12, 2021 2:12 am 
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Joined: Mar Sun 20, 2016 11:04 pm
Posts: 1117
Location: Mesa, AZ 85206
I am lucky because I live close to both circuit specialists and AES and I just pick things up, saving on shipping.

Circuit specialists is cheaper on somethings, but AES has a different inventory.

If I can get things locally, I do..even if is a bit more money. I like supporting AES..They are great people!

For example, I needed a 6AT6 fro a tube tester I am rebuilding....$4...

I used to go there years ago before they went internet.

Steve


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 Post subject: Re: Heathkit v-7a DC Probe
PostPosted: Sep Sun 12, 2021 3:36 am 
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Joined: Aug Wed 04, 2021 3:43 pm
Posts: 124
Notimetolooz wrote:
One of the smart things to do in this business is to order everything from one source to reduce shipping costs.
Antique Electronic Supply isn't the most inexpensive source for parts but if they have something other places don't have it may be worth it.
1N4007 rectifier diodes are used for may power supply applications, they can handle an ampere and as much as 1000V. Inexpensive 25 cents, get 10 or 12.
I found a 22uF 160V capacitor that will do, 200V would be optimum but they don't have any that are too much capacitance or too much voltage (you wouldn't want 400V). A little more capacitance than the original won't hurt in a power supply, a bit more voltage is a good idea but you shouldn't go too far.
There are much more affordable places to get tubes, but if you really want to up the total they have the 12AU7 tubes. Audio equipment uses 12AU7 tubes often, so they are in demand so $$$.
Switches in old electronics often get corroded or dirty and cause random operation. Cleaning switches and controls is always something to put on your list of things to do.


I ended up using a 1N4007 and a 24uf 200v capacitor. Worked nice. I also exercised all the front switches 50 times each. I found a place locally today called MRAM and they had a decent phone plug for $3. Of course I bought more stuff then I needed there lol. I didn't get any RG-174 or a probe. I'm sure I could have dug it out but it was noon in Central Florida and the sun was blazing. They keep the coax cable outside

Attachment:
20210911_113823.jpg
20210911_113823.jpg [ 3.04 MiB | Viewed 383 times ]


The AC scale is working perfectly. I can't test the DC scale until I get or make a DC probe. On the resistance scale the needle drifts towards infinity and past it to the right....according to the manual it's the battery which is brand new and making good contact or the resistor string is open someplace. I'm slowly testing each of the resistors and hopefully find the culprit.

Thanks for all the help and insight. This forum is great and I appreciate you all.
Robb

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Robb


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 Post subject: Re: Heathkit v-7a DC Probe
PostPosted: Sep Sun 12, 2021 3:07 pm 
Member

Joined: May Thu 14, 2015 4:15 pm
Posts: 3515
Location: Dallas, TX
Robbdoe1 wrote:

I found a place locally today called MRAM and they had a decent phone plug for $3. Of course I bought more stuff then I needed there lol. I didn't get any RG-174 or a probe. I'm sure I could have dug it out but it was noon in Central Florida and the sun was blazing. They keep the coax cable outside


The AC scale is working perfectly. I can't test the DC scale until I get or make a DC probe. On the resistance scale the needle drifts towards infinity and past it to the right....according to the manual it's the battery which is brand new and making good contact or the resistor string is open someplace. I'm slowly testing each of the resistors and hopefully find the culprit.

Thanks for all the help and insight. This forum is great and I appreciate you all.
Robb

For decades I used to have a place like that to get stuff until last year. Shut down because of the pandemic and rent increase. Enjoy it while it lasts.
Did you try the ohms adjustment on front?
If I remember right you can do some internal adjustments without the DC probe.

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Tim
It's not the Destination, It's the Journey.


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 Post subject: Re: Heathkit v-7a DC Probe
PostPosted: Sep Sun 12, 2021 10:11 pm 
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Joined: Aug Wed 04, 2021 3:43 pm
Posts: 124
I haven't tried yet but I will. I've got way too many projects going on at once lol.

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Robb


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