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 Post subject: Hickok 533 -> 533A (or similar) upgrade?
PostPosted: Nov Tue 13, 2007 5:37 pm 
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Joined: May Sat 26, 2007 8:07 pm
Posts: 52
Location: Norway
I have a couple of old Hickoks, and wonder;
Would it be a problem to update/modify an older tester to a later spec? (change signal voltage from 5V to 2,5V, and use later chart)
I have (and had) some Hickok that measure low on the 5V, and thinking of 3 ways to correct: add winding(not always practical), add another trafo for the 5V winding only, or reduce to the later spec. 2,5V, wich seems more interesting & practical..?

Arne K


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 Post subject:
PostPosted: Nov Fri 16, 2007 5:58 pm 
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Joined: May Sat 26, 2007 8:07 pm
Posts: 52
Location: Norway
:?: Is there any reason that this should not work?
- or have I overlooked anything?
As far as I can see, all other voltages are the same...

Arne K


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 Post subject:
PostPosted: Nov Fri 16, 2007 8:40 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 25381
Location: Pocasset, Cape Cod, MA
It's not practical. The A versions use more sensitive meters, and different values of resistors. I'm at work now, but can check the meter ratings when I get home.


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 Post subject:
PostPosted: Nov Fri 16, 2007 8:57 pm 
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Joined: May Sat 26, 2007 8:07 pm
Posts: 52
Location: Norway
:o You are right about meters: 533: 1,4mA / 80 ohm, 533A: 500uA / 233 ohm.

Arne K


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 Post subject:
PostPosted: Nov Fri 16, 2007 11:06 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 25381
Location: Pocasset, Cape Cod, MA
I've read about other owners having low 5V windings too. I believe that Hickok compensated for it elsewhere in the circuit, and shipped the instruments anyway.


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 Post subject: Re: Hickok 533 -> 533A (or similar) upgrade?
PostPosted: Aug Tue 26, 2014 1:47 am 
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Joined: Jun Wed 04, 2014 2:50 pm
Posts: 64
I have a 533A silver plate. I calibration company said that I have a low 5 volt signal winding of 4.6 and my testers transformer is failing so he could not calibrate. I thought the 533A had a 2.5 signal voltage?


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 Post subject: Re: Hickok 533 -> 533A (or similar) upgrade?
PostPosted: Aug Tue 26, 2014 2:23 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 25381
Location: Pocasset, Cape Cod, MA
Maybe it uses 5V for the lowest Gm range? I don't own one.


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 Post subject: Re: Hickok 533 -> 533A (or similar) upgrade?
PostPosted: Aug Tue 26, 2014 2:24 am 
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Joined: Aug Tue 13, 2013 3:18 am
Posts: 1095
Location: Milwaukee, Wisconsin
I have a 533A, and my understanding is if you only press P4, you get the 5v. But if you press P1 and P4, you get the 2.5v. If you look through the charts, you'll see which tubes it tells you to test using both buttons. I've always understood that to mean only certain tubes benefited from the smaller voltage.

Edit: I think I was half wrong. I looked back at the calibration instructions, and that only applies to the screen voltage and the plate is either 5 o 2.5 based on if it's A or not. At least I think. I just read the dang thing and my mind blanked out by the time I got back up to my computer!


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 Post subject: Re: Hickok 533 -> 533A (or similar) upgrade?
PostPosted: Aug Tue 26, 2014 1:12 pm 
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Joined: Jun Wed 04, 2014 2:50 pm
Posts: 64
Alan I am referring to your post from recent past that talks about " I've read about other owners having low 5V windings too. I believe that Hickok compensated for it elsewhere in the circuit, and shipped the instruments anyway. Maybe this what is possibly happening in my 533A where the service tech from Scherrer says my 5 volt signal winding is low 4.6 v. ( bad Transformer?)


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 Post subject: Re: Hickok 533 -> 533A (or similar) upgrade?
PostPosted: Aug Tue 26, 2014 7:25 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 25381
Location: Pocasset, Cape Cod, MA
Well if the winding is 4.6V now, it always has been. There's no way to "lose turns." I expect you could sneak a couple more in, through some gap in the windings, but whether the unexpected capacitance to other windings would be a problem, I couldn't say. There's not much to lose by trying it. Of course if you have to ship the tester to someone else to find out if it works, the expense mounts, not to mention the risk of damage.


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 Post subject: Re: Hickok 533 -> 533A (or similar) upgrade?
PostPosted: Aug Tue 26, 2014 8:07 pm 
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Joined: Jun Wed 04, 2014 2:50 pm
Posts: 64
Alan Is this the case you were referring too where the 5 volt secondary was low from the factory, Do this winding prevent the tester from being calibrated? Transformer don't weaken? they either work or fail (short out) ?
I'm not sure what is valid after the report from this service guy?
Does any one know of a QUALIFIED service place I can send my hickok 533A to get tested ?
or should i believe this other guy that the tester has a bad transformer and its not worth restoring


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 Post subject: Re: Hickok 533 -> 533A (or similar) upgrade?
PostPosted: Apr Sat 04, 2020 12:57 am 
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Joined: Oct Mon 10, 2011 3:03 am
Posts: 19
Bkisker wrote:
I have a 533A silver plate. I calibration company said that I have a low 5 volt signal winding of 4.6 and my testers transformer is failing so he could not calibrate. I thought the 533A had a 2.5 signal voltage?


I know this is an ancient thread, but that's what the OP stated. He has a 533 that uses 5.0v for the grid signal voltage - too high for tubes like the 12AX7. He wanted to know if he can modify it to use 2.5v like the 533A. I say that can be done because I have one - although it came from the factory like that! Has all the features of a 533A EXCEPT the meter, and it reads a calibration 6L6 on the money, as well as 12AX7(A) tubes. I've included some photos.

Richard


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 Post subject: Re: Hickok 533 -> 533A (or similar) upgrade?
PostPosted: Sep Fri 18, 2020 3:52 am 
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Joined: Oct Thu 04, 2018 2:11 pm
Posts: 444
Location: Suburban Chicago
Changing the grid drive voltage is simple, two 500 Ohm, 1/2 W resistors (R29 and R30 below). I don't know what changes to the metering circuit are required. In theory if you cut the drive voltage in half you double the scale of the meter readings so 3000 umho becomes 6000, etc. The simple minded approach of adding a shunt across the meter may or may not work well enough. Some experimentation will be required since Hickok changed the 533A meter instead of shunting the old one to make it come out right again at the lower voltage.

Attachment:
Hickok_533_Vs_533A_Grid.png
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 Post subject: Re: Hickok 533 -> 533A (or similar) upgrade?
PostPosted: Sep Sat 19, 2020 4:54 am 
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Location: Lincoln City, OR 97367
khutch wrote:
Changing the grid drive voltage is simple, two 500 Ohm, 1/2 W resistors (R29 and R30 below). I don't know what changes to the metering circuit are required. In theory if you cut the drive voltage in half you double the scale of the meter readings so 3000 umho becomes 6000, etc. The simple minded approach of adding a shunt across the meter may or may not work well enough. Some experimentation will be required since Hickok changed the 533A meter instead of shunting the old one to make it come out right again at the lower voltage.

Attachment:
Hickok_533_Vs_533A_Grid.png


I don't believe that this approach will work. The meter scale doubles because the average current through the meter is 1/2 what it would be for a five volt grid signal. Shunting a meter makes it LESS sensitive.... not more sensitive.

There are four approaches that might work; none of them is easy.

1. Replace the meter with one that is considerably more sensitive and juggle shunts and series resistors to bring it back to 80 ohms with double the sensitivity. Good luck on getting a dial card that looks even close to original.

2. Re-invent the tube chart with different values of the "English" pot setting and the expected Gm values to correct for the changes. Lotta work, IMHO.

3. Build a meter amplifier to double the drive to the meter. This is probably the easiest, but is fraught with potential problems.... uniform gain over the expected range? Temperature stability? Requirement for high quality regulated power... elaborate separate power supply.

4. Give up on the English scale and use only the fixed Gm scales; multiplying by 2 in your head for all readings. You might be successful in changing the fixed resistors for the switched Gm scales to save you the trouble of multiplying in your head, but you will never get the English scale right.

Regards,

_________________
Jim T.
KB6GM


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 Post subject: Re: Hickok 533 -> 533A (or similar) upgrade?
PostPosted: Sep Tue 22, 2020 3:04 am 
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Joined: Oct Thu 04, 2018 2:11 pm
Posts: 444
Location: Suburban Chicago
Yes, you are right, the shunt idea is backwards, so scratch that one.

1) might not be so hard if you are patient. Seems like people occasionally part out Hickoks on the bay so you will eventually find a suitable meter with the scale already in place. Might not be cheap however.

4) I should be getting a 533A soon. With nothing else to do while waiting I have toyed with the idea of adding a switch to give gate drives of 1.25 and 5 V and mentally adjusting the scales. Not saying I would actually do it, an idle mind is the devil's playground!


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 Post subject: Re: Hickok 533 -> 533A (or similar) upgrade?
PostPosted: Sep Tue 22, 2020 12:55 pm 
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Joined: Nov Wed 30, 2016 7:35 pm
Posts: 8274
Location: Sunbury, Ohio 43074
Seems to me it would be a LOT faster, much more accurate, and kinder to equipment if you'd just consider buying another tester that already does what you want :)

Modifying things like this, and you really will never know if your tube setting charts are going to produce accurate tests anymore?

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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: Hickok 533 -> 533A (or similar) upgrade?
PostPosted: Sep Tue 22, 2020 2:22 pm 
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Location: Suburban Chicago
Many of the older Hickoks provide 5 V grid drive which is too much for "modern" tubes like the 12AX7, or so people claim. The Hickok models that "do what we want to do" are highly prized by collectors, audiophiles, tube dealers, and radio restorers and so they command premium, often obscene, prices. Thus the common desire to modify older Hickoks that are often available at quite reasonable prices. Telling people they should use equipment they cannot afford is not the answer. Helping them get the results they need from equipment they can afford is the answer, if a simple and foolproof way can be worked out. I'm an electrical engineer, it is the sort of thing I do by nature. But in this case I am not highly motivated so this is more of a thought experiment for me.

There is no such thing as a tube tester that gives accurate numbers. The better tube testers give consistent numbers that have some success at predicting how well a tube will operate in the mythical typical circuit. Many Hickok models are examples of this kind of tester. If you want accurate numbers then you need a test system that can be adjusted to measure every tube under its specified operating conditions. Only lab grade tube measuring systems used by tube manufacturers and large, well off tube equipment manufacturers can do that. And if you can find one for sale it will take the concept of obscene prices to a new level. Actually, the best way for hobbyists to get that sort of accuracy is with modern digital tools like the uTracer and its more expensive cousins. And I have one of those too, thus the limited motivation on my part to do much work on my Hickok.


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 Post subject: Re: Hickok 533 -> 533A (or similar) upgrade?
PostPosted: Sep Tue 22, 2020 2:32 pm 
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Joined: Nov Wed 30, 2016 7:35 pm
Posts: 8274
Location: Sunbury, Ohio 43074
khutch wrote:
Telling people they should use equipment they cannot afford is not the answer. Helping them get the results they need from equipment they can afford is the answer, if a simple and foolproof way can be worked out. I'm an electrical engineer, it is the sort of thing I do by nature. But in this case I am not highly motivated so this is more of a thought experiment for me. Excuse me lol. I did not "Tell" anyone what to do, nor do I know what someone can or can not afford. I suggested an alternate, currently available option that others may be interested in. Those that are not, can just skip on to other things. There are also well respected tube testers that are not Hickok, possibly yet another alternate path depending on one's needs :)

There is no such thing as a tube tester that gives accurate numbers. The better tube testers give consistent numbers that have some success at predicting how well a tube will operate in the mythical typical circuit. Many Hickok models are examples of this kind of tester. If you want accurate numbers then you need a test system that can be adjusted to measure every tube under its specified operating conditions. Only lab grade tube measuring systems used by tube manufacturers and large, well off tube equipment manufacturers can do that. And if you can find one for sale it will take the concept of obscene prices to a new level. Actually, the best way for hobbyists to get that sort of accuracy is with modern digital tools like the uTracer and its more expensive cousins. And I have one of those too, thus the limited motivation on my part to do much work on my Hickok.
This isn't actual news.... what you state here is well known fact, even though we have to educate some newcomers occasionally, or break the equation down a bit even for non-newcomers. And to take this one step further, the "magic" done by the tube manufacturers and their very expensive instruments is quite lost to history. Besides which, even those were likely subject to a rather large tolerance range for any given tube.

It all boils down to my favorite platitude.... neither tubes, nor tube testers, were, are, or will ever be, precision devices.

The curve tracer may be the closest for general purpose use, although one could engineer a tester for one specific tube I suppose. But to what end? :)

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


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