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 Post subject: Re: What is the difference between the Hickok 533 and 533A
PostPosted: Apr Wed 01, 2020 5:02 pm 
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This doesn't totally apply to the 533/A,,, but just for those who are curious about :
This is a 201A vacuum tube on a Hickok 600A
Bias set to 48
Yellow trace is Plate voltage
White trace is Grid voltage


Attachments:
rsz_1hickok600a_voltages.jpg
rsz_1hickok600a_voltages.jpg [ 104.15 KiB | Viewed 211 times ]

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 Post subject: Re: What is the difference between the Hickok 533 and 533A
PostPosted: Apr Wed 01, 2020 10:09 pm 
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I am not sure where you are going with the grid signal voltage, it is usually tapped off of transformer (60 Hz) at a fixed voltage (5V) and then on some models there is a series of voltage divider resistors to tap off the appropriate signal voltages depending on the Hickok model. The particular model and roll chart are based off of the signal voltage, it is something not to change. On my 539B I did adjust the resistors to give the appropriate signal level for each Gm selector setting. On the 580 series the signal voltage is much lower. Another significant fault of most Hickok tube testers is the inability to zero the GM with no signal, i.e. balance the transformer to a Gm of 0. The TV-2 does have this feature, I have added this to my 539B and also the 580A for each plate voltage tap. The error is significant as you switch voltage taps, and directly heated tubes are usually read grossly wrong for multiple reasons on Hickok tube testers.

The Gm reading you get from different tube testers is just a number, and some cases just a percentage of what is considered good. You can make that number to come out to almost any Gm by fiddling with the bias V and shunt if you have one. The readings they give are arbitrary and probably represent a Gm target for the general parameters for each tube given. That they somewhat compare in a number doesn't really amount to much. Not sure why there is such an obsession with all this, if all the tube parameters were set the same between two tube testers, then yes I would expect them to be close in readings. That is what I outlined in setting the parameters the same between different tube testers (even though they derive the Gm differently) the tube results were close.

Using a regulated DC bias voltage in a Hickok tube tester will give you more error in your Gm and plate current then using unregulated. This was previously described (by Cdoose) and modeled to show why this occurs.


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580A.jpg
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 Post subject: Re: What is the difference between the Hickok 533 and 533A
PostPosted: Apr Wed 01, 2020 11:25 pm 
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mksj wrote:
I am not sure where you are going with the grid signal voltage, it is usually tapped off of transformer (60 Hz) at a fixed voltage (5V) and then on some models there is a series of voltage divider resistors to tap off the appropriate signal voltages depending on the Hickok model. The particular model and roll chart are based off of the signal voltage, it is something not to change. On my 539B I did adjust the resistors to give the appropriate signal level for each Gm selector setting. On the 580 series the signal voltage is much lower. Another significant fault of most Hickok tube testers is the inability to zero the GM with no signal, i.e. balance the transformer to a Gm of 0. The TV-2 does have this feature, I have added this to my 539B and also the 580A for each plate voltage tap. The error is significant as you switch voltage taps, and directly heated tubes are usually read grossly wrong for multiple reasons on Hickok tube testers.


Thanks but I'm not looking to add or change anything right now. Your answer seems to support my theory that this board with the wire wound resistors is in fact the voltage divider that Hickok added to the 533 circuit that sets it apart and was incorporated into the 533A. Does anyone understand what I'm asking? Please!

Richard

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 Post subject: Re: What is the difference between the Hickok 533 and 533A
PostPosted: Apr Thu 02, 2020 12:52 am 
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Barry H Bennett wrote:
I've got a 533 in "as bought" condition.... in other words, unknown. If you get stuck with yours by other means, I can pull mine out and get you any kind of measurements you may need. Might be an excuse for me to check the restoration / calibration of mine at the same time. Let me know.


Thanks, Barry! So does your 533 have this board near the transformer, with a couple of wirewound resistors on it?


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IMG_4697.JPG
IMG_4697.JPG [ 681.64 KiB | Viewed 197 times ]

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 Post subject: Re: What is the difference between the Hickok 533 and 533A
PostPosted: Apr Thu 02, 2020 1:20 am 
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I will try and remember to pull it off the shelf tomorrow (it's at the shop) and take a peek. :). If I forget (likely) you won't upset me by bugging me to do it again

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 Post subject: Re: What is the difference between the Hickok 533 and 533A
PostPosted: Apr Thu 02, 2020 1:24 am 
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Barry H Bennett wrote:
I will try and remember to pull it off the shelf tomorrow (it's at the shop) and take a peek. :). If I forget (likely) you won't upset me by bugging me to do it again


Thank-you, Barry! (Dustin Hoffman, on accepting the Best Actor Oscar for his performance in "Rain Man")

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Last edited by richardbruce on Apr Thu 02, 2020 1:48 am, edited 1 time in total.

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 Post subject: Re: What is the difference between the Hickok 533 and 533A
PostPosted: Apr Thu 02, 2020 1:28 am 
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No I do not believe you have the correct resistors if you look at thee schematic and the resistor values. The difference between the grid signal between the 533 and 533A is the addition of a voltage divider resistor R29/R30 which are =500 ohms on the 533A. So there would be two resistors acting as a voltage divider. There is very little current so I would expect this resistor to be 1/4 or 1/2W. On the 539B if I recall there are a string of 1/4W dividing resistors. Is there any indication of the value of the spool resistor, it is not the other wire wound resistors on the board?


Attachments:
533.jpg
533.jpg [ 275.42 KiB | Viewed 195 times ]
533A.jpg
533A.jpg [ 246.49 KiB | Viewed 192 times ]
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 Post subject: Re: What is the difference between the Hickok 533 and 533A
PostPosted: Apr Thu 02, 2020 2:01 am 
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mksj wrote:
No I do not believe you have the correct resistors if you look at thee schematic and the resistor values. The difference between the grid signal between the 533 and 533A is the addition of a voltage divider resistor R29/R30 which are =500 ohms on the 533A. So there would be two resistors acting as a voltage divider. There is very little current so I would expect this resistor to be 1/4 or 1/2W. On the 539B if I recall there are a string of 1/4W dividing resistors. Is there any indication of the value of the spool resistor, it is not the other wire wound resistors on the board?


Thanks for replying and for posting those schematic shots. I have been unable to find a 533A schematic in a readable file format. But it only shows the addition of one fixed resistor R29 and subbing a variable for R6. I'm curious - how do you know the values?

And yes, there is also a bobbin resistor on the board (see the photo).

In any case, Barry is going to open his 533 tomorrow and see if that same "daughter" board is in his.

Richard


Attachments:
IMG_4697.JPG
IMG_4697.JPG [ 681.64 KiB | Viewed 192 times ]

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 Post subject: Re: What is the difference between the Hickok 533 and 533A
PostPosted: Apr Thu 02, 2020 3:03 am 
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Parts description is in the manual.


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533A resistors.jpg
533A resistors.jpg [ 254.11 KiB | Viewed 189 times ]
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 Post subject: Re: What is the difference between the Hickok 533 and 533A
PostPosted: Apr Thu 02, 2020 4:23 am 
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mksj wrote:
Parts description is in the manual.


The parts list you posted seems to confirm my suspicions - that the 533 I purchased in is essence a 533A. Resistors R1, R12, and R13 are the wirewound resistors on the little board bolted just above the transformer and to the inside of the tester. I'm guessing the spool resistor is listed as well, although I'll have to open it up again and compare it to the schematic and list. Another tube tester repair tech that I heard from first suggested the presence such a phenolic board without even seeing my photos.

I guess the only other thing left to do is actually measure the voltage. That will confirm if the 533 I bought, which resembles a 533A so many other ways, is indeed a very early 533A with a 533 label. Anyone else have any input? Feel free to comment.

Richard

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 Post subject: Re: What is the difference between the Hickok 533 and 533A
PostPosted: Apr Thu 02, 2020 5:30 am 
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UPDATE: I couldn't go to bed until I checked the bias voltage myself. Per instructions, I set my 533 to test a 6L6. I then measured the voltage between pins 5 and 8 on the octal socket. The bias voltage measures 2.51v, confirming that this in fact a 533A tester labeled as a 533! More later...

Richard

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 Post subject: Re: What is the difference between the Hickok 533 and 533A
PostPosted: Apr Thu 02, 2020 3:53 pm 
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Barry H Bennett wrote:
If I forget (likely) you won't upset me by bugging me to do it again


Measured the bias voltage last night, Barry - 2.5v. So it must be a very early 533A with a 533 label on it. Perhaps Hickok got tired of waiting for the silkscreener.

Still, it would be interesting to know if your 533 has that same board. Have you ever measured the grid signal voltage on your 533?

Richard

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 Post subject: Re: What is the difference between the Hickok 533 and 533A
PostPosted: Apr Thu 02, 2020 4:47 pm 
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If you read up about Hickok testers, you will find that the schematics do not necessarily represent the version that you have and that there were constant changes done on the production line. So even with the same model you can see many build variants. You can also go on-line and there are many pictures of the the different models versions. Below is the a comparison of an old 533 version vs. 533A. As I indicated the board has nothing to do with the grid signal, they did not use spool or wire wound resistors for the grid signal dividers.


Attachments:
Hickok 533 and 533A Phenolic Board.jpg
Hickok 533 and 533A Phenolic Board.jpg [ 356.22 KiB | Viewed 170 times ]
Hickok 533A-2.jpg
Hickok 533A-2.jpg [ 760.81 KiB | Viewed 170 times ]
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 Post subject: Re: What is the difference between the Hickok 533 and 533A
PostPosted: Apr Thu 02, 2020 5:22 pm 
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mksj wrote:
If you read up about Hickok testers, you will find that the schematics do not necessarily represent the version that you have and that there were constant changes done on the production line. So even with the same model you can see many build variants. You can also go on-line and there are many pictures of the the different models versions. Below is the a comparison of an old 533 version vs. 533A. As I indicated the board has nothing to do with the grid signal, they did not use spool or wire wound resistors for the grid signal dividers.


As you can see, the last photo you uploaded 533A-2.jpg is the same as the one in my tester. And by measuring the grid signal, I can confidently say that both the panel of my tester and the circuits below it are indeed 533A, and not 533 as indicated by the label. I'm very pleased with my purchase now. Thanks for your help!

Richard


Attachments:
case01.jpg
case01.jpg [ 41.38 KiB | Viewed 168 times ]
case02.jpg
case02.jpg [ 44.15 KiB | Viewed 168 times ]
my533A.jpg
my533A.jpg [ 67.41 KiB | Viewed 168 times ]
IMG_4697.JPG
IMG_4697.JPG [ 681.64 KiB | Viewed 168 times ]

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 Post subject: Re: What is the difference between the Hickok 533 and 533A
PostPosted: Apr Thu 02, 2020 10:01 pm 
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Ok, I brought it home. Next step is to get the Heathkit IO4550 10MHz scope that I am mercy fixing for a friend, off the bench. I've already got way more time and parts into it than it's worth but.... well you know. Got two good traces but won't trigger. <sigh>. yet...

Then the 533... hopefully by tomorrow morning. There seems to be plenty of time ....

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 Post subject: Re: What is the difference between the Hickok 533 and 533A
PostPosted: Apr Thu 02, 2020 10:38 pm 
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Barry H Bennett wrote:
Ok, I brought it home. Next step is to get the Heathkit IO4550 10MHz scope that I am mercy fixing for a friend, off the bench. I've already got way more time and parts into it than it's worth but.... well you know. Got two good traces but won't trigger. <sigh>. yet...

Then the 533... hopefully by tomorrow morning. There seems to be plenty of time ....


Thanks, Barry! But if you check my posts, I've determined that the (one-off?) tester I bought isn't a 533 but a 533A. I verified that by measuring the grid signal bias voltage. The 533 had a 5.0v grid signal bias voltage, while the 533A used a 2.5v grid signal bias voltage. Mine measured 2.5-something. Still curious...

Richard

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 Post subject: Re: What is the difference between the Hickok 533 and 533A
PostPosted: Apr Sun 05, 2020 1:24 pm 
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Photos for posterity ....... this one needs full restore especially the case. Musty.


Attachments:
F9434461-F823-4805-A78E-F21C952C9C25.jpeg
F9434461-F823-4805-A78E-F21C952C9C25.jpeg [ 3.14 MiB | Viewed 150 times ]
5D4F1CE3-3255-4C77-9D62-0A24025F7DF3.jpeg
5D4F1CE3-3255-4C77-9D62-0A24025F7DF3.jpeg [ 3.04 MiB | Viewed 150 times ]

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 Post subject: Re: What is the difference between the Hickok 533 and 533A
PostPosted: Apr Sun 05, 2020 10:44 pm 
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Barry H Bennett wrote:
Photos for posterity ....... this one needs full restore especially the case. Musty.


Why fully restore? Isn't it working right? I hear that if one is working, it's best not to mess around a lot.

Richard

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 Post subject: Re: What is the difference between the Hickok 533 and 533A
PostPosted: Apr Sun 05, 2020 10:59 pm 
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It’s musty, moldy, the power cord is falling apart, and the switches are badly oxidized.....the usual stuff. I don’t dare even plug it in this way

Not my first rodeo.... fear not. It’s in the que behind a lot of others

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