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  #16  
Old 01-09-2013, 12:58 PM
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earlyfilm earlyfilm is offline
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Geoff,

I still feel that something is missing in your pot.

Tonight, I'll pop the pot out of my 540 and see what it looks like on the chassis side.

I cannot fully disassemble it, for the war production models, they did not use lugs, but soldered the wires directly on to the brass-bolt threads.

Duh!

James
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  #17  
Old 01-09-2013, 11:10 PM
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Geoff Geoff is offline
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Thanks James but I have since fixed the issue. I left the wiper in place and put a small bend on the section that makes contact with the bushing.



I then sprayed some DeOxit onto my finger and wiped it across the brass bushing. Then I put everything back together and tested the pot. It now works like it should! Wow, getting those c-clips off is a real pain in the butt. The first time I took it off it was fairly easy. This last time was hard and I ended up breaking it. You can see the broken half in the photo. I'll need to head down to Ace Hardware and see if they have some. In the meantime I used a small piece from a paper clip to hlod the shaft in place.

One last question. Any issues with applying DeOxit where the wiper makes contact with the tapered resistance element? I wasn’t thinking of spraying the whole thing. Just spraying some on my finger again and wiping it only in the area where the wiper makes contact with it. I know there have been warnings about spraying the wafers on the switch contacts. From what I have read the wafers can absorb the spray and then intermittents abound.

Thanks,
Geoff
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  #18  
Old 01-10-2013, 05:25 AM
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earlyfilm earlyfilm is offline
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Geoff,

Congratulations!

Re: The deoxit style cleaners

IMHO, this style cleaner works extremely well for the short time, but they dry just sticky enough to attract dust which later causes problems. Since the shaft area of the old style pots are not exposed to that much dust, you solution of using this cleaner on the shaft is probably OK.

I took pictures last night, but thought I'd sleep on it before posting a reply, so I'll post them anyway as a possible aid for anyone else who is thinking about disassembling one of these Hickok pots with the pre-war design.

In the older design like yours, the engineering seems not been too well thought out and the "C" clip probably completes the electrical circuit better than the brass bearing.

In the newer design contact plate (the one that I formerly thought was missing in your case) has been moved to the inside of the pot and it is more trouble free.

If you stop and think about it, this pot is only rotated when the power is off. In other words, electricity only flows when you press the test button, so this design does not have to be noise-free while turning.

I'd only had experience with the newer design.

James
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Last edited by earlyfilm; 01-10-2013 at 08:00 AM. Reason: reworded sentence
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  #19  
Old 01-10-2013, 09:25 AM
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Geoff Geoff is offline
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Thanks James!

- Geoff
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  #20  
Old 01-24-2013, 03:02 PM
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Geoff Geoff is offline
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I was reading the calibration procedure for the Hickok 600A written by Daniel Schoo and I also watched the 2 YouTube videos by Bob Anderson entitled “Hickok 600A Restoration”. In Daniel Shoo’s article it states:

MUTUAL CONDUCTANCE READING TEST
Verify that the panel switches are set up to the conditions as given in PREPARATION at the beginning of this section, (JR 5347-2) FILAMENT at 6.3 volts. Set the BIAS and the ENGLISH controls to zero. Rotate the ENGLISH control clockwise to the orange dot near number 73.

For the following mutual conductance test you will need to set up an isolated current limited source of AC voltage. Use the setup drawing in figure 1 to connect the equipment to the tester. Be careful because improper connection can cause serious damage. Connect the source to pins 8 and 3 of the octal socket. If the main meter deflects downward instead of up when you perform the test, swap the connections to pins 8 and 3. Measure the voltage source directly across the secondary of the isolation transformer. Do not use a shunt resistor across the meter.


FIGURE 1

Push P4 and slowly adjust the voltage source up to exactly 50.0 volts. Observe the reading on the tester meter. The correct reading is 2000 micromhos plus or minus one small division on the 3000 scale. It may be slightly worse depending on the quality of the ENGLISH control. After taking the reading set the voltage back to zero and release P4.

So the directions state Set the BIAS and the ENGLISH controls to zero. Rotate the ENGLISH control clockwise to the orange dot near number 73. Those correspond to the different scales (3000, 6000, 15000). #My 533 does not have the orange dot near number 73 on the ENGLISH dial, but it does have a separate switch for the scales (3000, 6000, 15000). #Would I be correct in assuming that I could set the ENGLISH dial (and BIAS) to zero, set the range switch to 3000, apply the 50V as detailed in the procedure, and expect a reading of 2000 micromhos (assuming everything else is working properly)? #If it was not at 2000 I would follow the Control Alignment Procedure as detailed in the article and demonstrated in the YouTube video.

I think it should work but I’d like to bounce off you guys as a sanity check before I try it.

Thanks,
Geoff
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