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 Post subject: Jackson 658 Tube Tester
PostPosted: Mar Sat 14, 2020 10:15 pm 
Member

Joined: Jan Thu 24, 2019 1:22 pm
Posts: 316
Location: Centennial, Colorado 80122
Some time ago I picked up a Jackson 658-1 simply because it was in immaculate condition and I was curious about the measuring circuits used. Now that I have backed off of manufacturing items and servicing of the Hickok 539B/C tube testers I had time on my hands to take a look. It is in operating condition giving results close to what I expected. Eric Knutsons had done a lot of work analyzing the circuits and I decided to use his Calibration Instructions for two reasons one I could check the calibration and two it would hasten my understanding of the circuits.

As with my procedures for the Hickok Testers I first checked the meter and found a discrepancy.
His specs were listed at 200uA and 155 ohms.
I found the specs for mine are 200uA and 30mV giving a resistance of 150 ohms.

Following his procedure for adjusting R29 that sets the sensitivity for the meter circuit it calls for 25mA to be fed between pins 3 and 8 of the octal socket using a DC source of appx. 70 VDC for a half scale reading of the meter. I found my unit to require 27.5mA to achieve half scale.

Without changing R29 on to the next adjustment which is connecting the tester to a variac set at 120VAC setting the Line Control to 120 and adjusting R20 to give a mid scale reading on the meter and I found it was extremely close. So I went back to the previous step and adjusted R29 to give half scale at 25mA and found it put me at the limit of R20 for the line adjustment at half scale.

From the overall condition of this tester and with the sockets as tight as you would expect new to be its likely it has seen very limited if any use nor were there any signs of service internally. With this in mind it made me question the specs Eric listed for the meter and if his adjustment of R29 was correct. I did go through the rest of his procedures and found everything worked out just fine.

So my question to any owners of a Jackson 658 in the group is has anyone checked the meter in their 658 or experienced any difficulty adjusting R20 after adjust R29. Also does anyone know how to contact Eric? I tried a search on here, but by no means always able to navigate this site.

Thanks, Bill


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 Post subject: Re: Jackson 658 Tube Tester
PostPosted: Mar Fri 20, 2020 11:17 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 49
Location: Central PA, USA
Hi Bill,

I purchased a Jackson 658 tester back in 2009. My Jackson had a calibration issue and I sent a series of private messages to Erik through the private messages tool on this forum at that time. Erik was kind enough to correspond with me on the issue I was experiencing. He made a number of suggestions which I attempted to implement. Then early in 2010 my father was diagnosed with lung cancer and I dropped trying to fix my Jackson. (I have a couple of other testers that I use routinely). My Jackson is still on my round to it list some ten years later. I don't know if Erik is still active on this forum but I sent him my private messages using this name on this forum Erik K

Ernie


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 Post subject: Re: Jackson 658 Tube Tester
PostPosted: Mar Sat 21, 2020 12:13 am 
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Joined: Jan Thu 24, 2019 1:22 pm
Posts: 316
Location: Centennial, Colorado 80122
Hi Ernie,

Thanks for responding and putting out a PM for Eric. Tomorrow morning I plan on posting a mod that adds plate current jacks to the 658. I am in the process of learning things about these tester and willing to help you if desired.

Bill


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 Post subject: Re: Jackson 658 Tube Tester
PostPosted: Mar Sat 21, 2020 3:12 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2325
Location: Potomac, MD 20854
I don't want to hijack this thread and will create a different post if appropriate.

I just acquired a 658A. Most of the markings around the HEATER TEST knob are worn away. I could put dots at the index points and stick little labels next to them, either directly on the panel or on a paper circle rubber-cemented to the panel, but I'd prefer a neater look.

What ideas come to mind?

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Avery W3AVE


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 Post subject: Re: Jackson 658 Tube Tester
PostPosted: Mar Sat 21, 2020 11:50 am 
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Joined: Nov Wed 30, 2016 7:35 pm
Posts: 11105
Location: Sunbury, Ohio 43074
Bill, I don't have a 658, but if I can help you out with these three, they're all on the shelf: 635, 648, 680

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https://www.bbtvtestequipment.com


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 Post subject: Re: Jackson 658 Tube Tester
PostPosted: Mar Sat 21, 2020 3:18 pm 
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Joined: Jan Thu 24, 2019 1:22 pm
Posts: 316
Location: Centennial, Colorado 80122
Avery it seems there are few members with the Jackson 658 series, so we might as well keep them all together. The Avery Company (do you own it) has clear labels for both the laser and inkjet printers that you might be able to use. If you do remember to give it a clear coat of lacquer.

Thanks Barry, but the 658 series are unique in the Jackson line of tube testers. That's what caught my eye and led to the purchase of one to satisfy the curiosity.

I contacted a member on the classified section about knobs and he was interested in my plate current mod for the 658, so ready or not I'm posting it here.


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 Post subject: Re: Jackson 658 Tube Tester
PostPosted: Mar Sat 21, 2020 4:17 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1566
Location: 07450, New Jersey
I have been using the 658 for years as my go-to tester, quick to set up and I trust it. It gives results comparable to my Heathkit TT-1A and RCA WT-100A. I have another one as a spare and also a parts unit (that is where I got the knob I offered in Avery's WTB post). One of the photos that Erik used in his cal instructions was of the board in my tester. I was communicating with him during the time he was writing his procedure. I recall that my meter measured 155 ohms as well and it calibrated per his instructions. I have since calibrated about 3 others.

Your plate current mod is interesting.

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Tim

"One of the advantages of being disorderly is that one is constantly making exciting discoveries." A. A. Milne


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 Post subject: Re: Jackson 658 Tube Tester
PostPosted: Mar Sat 21, 2020 4:57 pm 
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Joined: Jan Thu 24, 2019 1:22 pm
Posts: 316
Location: Centennial, Colorado 80122
Thanks Tim, These are interesting testers and the best I have ever seen for overcoming the voltage sag that most testers have. As I always do to verify the accuracy of the meter is to disconnect one end, then using a battery as the current source and a pot to to adjust it measure the current flow and the voltage across the meter at the same time. I do this at full and half scale with high quality digital meters. The results I got were dead on with what I posted. Is there any chance you might check one of your meters again?


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 Post subject: Re: Jackson 658 Tube Tester
PostPosted: Mar Sat 21, 2020 5:05 pm 
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Joined: Nov Wed 30, 2016 7:35 pm
Posts: 11105
Location: Sunbury, Ohio 43074
Tim, try one of these procedures to test your meter movement ......

https://www.bbtvtestequipment.com/testing-a-panel-meter

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Preserving the hist. of electronics, one boat anchor at a time! :)
https://www.bbtvtestequipment.com


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 Post subject: Re: Jackson 658 Tube Tester
PostPosted: Mar Mon 23, 2020 9:50 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1566
Location: 07450, New Jersey
Thanks Barry, I used method 2 when I measured years ago and calculated the resistance using Ohm's law. I will dig out my notes to be sure of my recollection and try and carve out some time to measure again.

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Tim

"One of the advantages of being disorderly is that one is constantly making exciting discoveries." A. A. Milne


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 Post subject: Re: Jackson 658 Tube Tester
PostPosted: Sep Mon 13, 2021 2:22 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1547
Location: St. Paul, Minnesota
Bill Eccher wrote:
Some time ago I picked up a Jackson 658-1 simply because it was in immaculate condition and I was curious about the measuring circuits used. Now that I have backed off of manufacturing items and servicing of the Hickok 539B/C tube testers I had time on my hands to take a look. It is in operating condition giving results close to what I expected. Eric Knutsons had done a lot of work analyzing the circuits and I decided to use his Calibration Instructions for two reasons one I could check the calibration and two it would hasten my understanding of the circuits.

As with my procedures for the Hickok Testers I first checked the meter and found a discrepancy.
His specs were listed at 200uA and 155 ohms.
I found the specs for mine are 200uA and 30mV giving a resistance of 150 ohms.

Following his procedure for adjusting R29 that sets the sensitivity for the meter circuit it calls for 25mA to be fed between pins 3 and 8 of the octal socket using a DC source of appx. 70 VDC for a half scale reading of the meter. I found my unit to require 27.5mA to achieve half scale.

Without changing R29 on to the next adjustment which is connecting the tester to a variac set at 120VAC setting the Line Control to 120 and adjusting R20 to give a mid scale reading on the meter and I found it was extremely close. So I went back to the previous step and adjusted R29 to give half scale at 25mA and found it put me at the limit of R20 for the line adjustment at half scale.

From the overall condition of this tester and with the sockets as tight as you would expect new to be its likely it has seen very limited if any use nor were there any signs of service internally. With this in mind it made me question the specs Eric listed for the meter and if his adjustment of R29 was correct. I did go through the rest of his procedures and found everything worked out just fine.

So my question to any owners of a Jackson 658 in the group is has anyone checked the meter in their 658 or experienced any difficulty adjusting R20 after adjust R29. Also does anyone know how to contact Eric? I tried a search on here, but by no means always able to navigate this site.

Thanks, Bill


Hi Bill,

Just to set the record straight, you never did send me a message about this. I have been a contactable member of this forum since 1999. My specs on the Jackson 658 meter were correct.

Erik K


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 Post subject: Re: Jackson 658 Tube Tester
PostPosted: Sep Mon 13, 2021 4:57 pm 
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Joined: Jan Mon 18, 2010 2:13 am
Posts: 22698
Location: Dayton Ohio
I'm sure there could be some slight variation in resistance. 5 ohms isn't much.

I'm sure they were aiming for the 200 μA accuracy over resistance accuracy.
Any variation can easily be compensated with the sensitivity pot.

Sadly every 200 μA meter I find have a resistance of 1400-1900 ohms.

The op-amp conversion I came up with seems to take care of this. :D

-Steve

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 Post subject: Re: Jackson 658 Tube Tester
PostPosted: Sep Mon 13, 2021 7:21 pm 
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Joined: Nov Wed 30, 2016 7:35 pm
Posts: 11105
Location: Sunbury, Ohio 43074
Let's name it a "Meter Matching Amplifier". Make T'shirts :)

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https://www.bbtvtestequipment.com


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