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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: 1092
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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"If something can go wrong with an old tube rig, someone probably knows what it was!"
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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: 417
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
Hickok_533_Vs_533A_Grid.png [ 407 KiB | Viewed 75 times ]


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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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Joined: Nov Mon 02, 2009 7:01 am
Posts: 4576
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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