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Old 4th Jun 2021, 8:03 am   #1
resurgance
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Default Hickok 539b bias gauge

Hi there,
I understand that Hickok is mainly US and AVO is more UK, so apologies if this is not quite the place for thjs question?
I have a 539b with a bias gauge sans adjuster but reading above zero.
Any ideas please on how to return this to zero?
It reads this way unpowered as well as powered.

Thanks
Stew Thorp
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Old 4th Jun 2021, 8:19 am   #2
paulsherwin
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Default Re: Hickok 539b bias gauge

You are right that Hickok stuff is mainly used in North America, so you might get a better response if you post on one of the US forums. We do have members from across the globe though, so somebody may have experience with one of these.
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Old 4th Jun 2021, 9:44 am   #3
mikko rintala
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Default Re: Hickok 539b bias gauge

Is this help? Mechanical Meter Zero
This pertains to all three meters on the set, but primarily to the MAIN METER. Before powering up the set, the physical zeroes of the meters should be checked and adjusted. This is done by turning the slotted screw head located at the center bottom of the meter. Note that the meter zero will, in general, be highly position dependent, especially for the MAIN METER. Change the physical orientation of the tester (and hence of the meters), and you will usually have to change this adjustment also. Just setting the tester on an angled surface will often be enough to require re-adjustment of one or more of the meters.

To calibrate the tester (and especially to make any changes to the set) you have to have access to the back of the set and it is/will be difficult to keep the MAIN METER physically zeroed. A way around this difficulty is to measure the voltage separately at the main meter terminal posts with a separate voltmeter using test clips/leads.

https://www.byan-roper.org/m_higgins...cal-meter-zero
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Old 4th Jun 2021, 10:15 am   #4
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Default Re: Hickok 539b bias gauge

Quote:
Originally Posted by mikko rintala View Post
Is this help? Mechanical Meter Zero
This pertains to all three meters on the set, but primarily to the MAIN METER. Before powering up the set, the physical zeroes of the meters should be checked and adjusted. This is done by turning the slotted screw head located at the center bottom of the meter.
I think the point here is looking at the picture there is no adjusting screw head in the position described above.

Cheers

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Old 4th Jun 2021, 10:55 am   #5
mikko rintala
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Default Re: Hickok 539b bias gauge

Can you remove the meter cover? If adjust is under that? It s have to be somewhere,the adjust screw.
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Old 5th Jun 2021, 1:27 am   #6
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Default Re: Hickok 539b bias gauge

Hi thanks for the replies - it does not appear to have a screw even under the cover but i will disassemble and investigate further. Surely it is mechanical?
Thanks
Stew
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Old 5th Jun 2021, 3:57 am   #7
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Default Re: Hickok 539b bias gauge

Upon removing the meter itself from the front panel, in bold letters is written "sealed do not open" so am not quite sure how to proceed carefully. I guess I'll offset bias for now manually.
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Old 5th Jun 2021, 12:18 pm   #8
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Default Re: Hickok 539b bias gauge

It could be one of two things if the pointer remains off set from zero with and without power applied to the tester.

Either one of the small internal pointer weights has moved throwing the movement out of balance, or there is a build up of static on the meter glass.

Removing the static is easy, just wipe the meter face with a damp cloth, or use an anti-static spray on the cloth.

Re-positioning, or re-installing the balance weight is a whole other level of difficulty.

I had the same problem with the meter in my Marconi VTVM, which turned out to be due to one of the balancing weights having fallen off the pin where it is supposed to sit. Those weights are rather small and look like tightly wound spirals.

I found the "missing" weight floating around inside the meter and consider myself lucky to have found it...!!

Good luck with resolving the issue...73...Jordan VE6ZT
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Old 5th Jun 2021, 1:22 pm   #9
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Default Re: Hickok 539b bias gauge

Quote:
"sealed do not open"
is a warning, much the same as "DANGER high voltage" or "No User serviceable parts", none of these warnings need apply to a careful and observant person.
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Old 5th Jun 2021, 7:33 pm   #10
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Default Re: Hickok 539b bias gauge

Question is can the meter be opened without destroying it? I've seen some where there is no obvious means of opening it.

David
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Old 6th Jun 2021, 12:07 am   #11
resurgance
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Default Re: Hickok 539b bias gauge

Hi thanks for the replies,
Jordan the static suggestion was great, unfortunately no change in needle position. I did have some spray there too.

Andrew - agreed totally! I do think I am fairly observant and careful but I have to say with regards to these older units there are a LOT of pitfalls. I wear wool as opposed to static generating clothing etc but some of these meter movements almost need a dedicated clean room and watchmaker precision. I wanted to find out more about what I was getting into before opening and irreversibly altering the action. Currently it is smooth and seems to be linear - but offset by 2.5v.

David this meter is one with no obvious means of opening apart from working around the edge and prying the folded over edge of the meter outward while fighting the adhesive that seems to be still present. I have experienced this in other things and this may not be the same, but they aren't really easy to reassemble to the same tight fit. Once something has been flared it almost needs a custom die set to get it back to a point where it can sit flat against the panel without then forcing the lid off again. That old thin pressed steel is quite springy. The side of the meter if pried off would look rough visually. And I just can't get one of these meters they don't seem to come up on ebay etc.

The front of the meter is wrapped around the edge of the body - which to me means there is some form of gasket in there. So if I attempt to open it I can imagine the shrapnel of this gasket will end up in the meter movement. They are so delicate! This just ends up reaffirming my awe of watchmakers and those that work in the macro and micro. Scale is an interesting thing.

Am tempted to offset it or measure it externally using a DMM while tube testing and leave the meter be.

Cheers and 73
Stew Thorp
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Old 12th Jun 2021, 12:22 am   #12
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Default Re: Hickok 539b bias gauge

The early 539B versions they had an external 0 adjust, later version were hermetically sealed and not adjustable, but seemed to vary. You will most likely damage the meter in breaking the seal. Although my 539B bias meter works correctly I use external digital meters to measure bias and plate current, the meters require isolated power supplies.

You may want to compare the meter readings to an external volt meter, it could be the movement is sticking, damaged movement, debris, etc.
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Old 12th Jun 2021, 12:33 am   #13
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Default Re: Hickok 539b bias gauge

Is it an option to replace the meter with another of same size and appearance it just looks like any other regular round meter from that period, you could draw up a new scale using a graphics program like Inkscape, print it, cut it out and glue it to the scale.
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Old 12th Jun 2021, 6:35 am   #14
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Default Re: Hickok 539b bias gauge

Some meters were made with their mechanical zero adjuster working on the rear spring reference position, having a screwdriver slot at the rear of the case. Have you checked under any label on the rear?

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