Author Topic: EEVblog #461 - Genrad Decade Resistance Box Teardown (Read 20524 times)

LaurenceW · « **Reply #25 on:** April 25, 2013, 08:40:24 am »

Dave, I assume with all those wound wires that this box is very much intended for DC work? There must be significant inductance in there.

Fantastic engineering on the switches, though.

mikes · « **Reply #26 on:** April 25, 2013, 11:29:54 pm »

Quote from: LaurenceW on April 25, 2013, 08:40:24 am

Dave, I assume with all those wound wires that this box is very much intended for DC work? There must be significant inductance in there.

They're made to handle AC, through at least audio frequencies, up to the 100K decades. The decades up to 100 ohms used Ayrton-Perry windings. The higher ohm ones do better than regular circular wirewound resistors, because of the flat card windings.

They publish specific impedance info in the manual.

BMac · « **Reply #27 on:** April 26, 2013, 11:29:56 am »

Dave,

Don't do it! Don't spray that beutiful piece of equipment with WD-40, Use WD-40 on your lawn tractor, but not that precision piece of equipment.
I am out of town, right now but when I get back I'll send you a can of Deoxit.

Cheers brother, love your blog!

BMac.

BMac · « **Reply #28 on:** April 26, 2013, 11:35:01 am »

Dave,

After you spray it with WD-40 you wont be able to stand the smell either.

BMac

WattSekunde · « **Reply #29 on:** June 11, 2013, 07:37:22 am »

Take a look at this old beautiful wheatstone bridge on eBay (I am not the seller an I don't know him).

http://cgi.ebay.de/ws/eBayISAPI.dll?ViewItem&item=251288222202

ftransform · « **Reply #30 on:** June 15, 2013, 12:22:55 am »

i want to demolish the cult that is deoxit. what the hell makes this crap so special ?

wd40 is used for nuclear missiles. fucking plutonium!

c4757p · « **Reply #31 on:** June 15, 2013, 12:35:37 am »

Quote from: ftransform on June 15, 2013, 12:22:55 am

i want to demolish the cult that is deoxit. what the hell makes this crap so special ?

The price.

Quote

wd40 is used for nuclear missiles. fucking plutonium!

Nah, plutonium doesn't do a very good job cleaning contacts. Not that I would know...

ftransform · « **Reply #32 on:** June 15, 2013, 01:27:40 am »

the KGB uses plutonium to "clean" contacts

robrenz · « **Reply #33 on:** June 15, 2013, 02:37:22 am »

Quote from: ftransform on June 15, 2013, 12:22:55 am

i want to demolish the cult that is deoxit. what the hell makes this crap so special ?

I am the cult leader

it is special because it works. If it is snake oil they have fooled me and Agilent and a host of other major industry leaders. I especialy like it in my espresso

PTR_1275 · « **Reply #34 on:** November 12, 2015, 12:39:09 pm »

I know this is quite an old thread, I would rather post in a thread which is related rather than there be hundreds of similar threads. I did try to find any other posts about this, but this was the one that came up.

I have recently bought a Genrad 1433 -G (0.1 - 100K 7 decade) box very similar to Dave's. Some of the switches are quite stiff to the point that I feel they will break, some of them feel magnificent. I thought it might have needed a bit of movement to free up the switches, but even after actuating the stuck switches close to 100 times each, they still feel very stiff.

The resistance is pretty darn accurate so I am not wanting to just jump in there with WD40 or anything, but I am worried about the stiff switches and am hoping someone can give me some advice on what to do.

I notice (like on Dave's) there is some grease / lubricant on the contacts, if I clean the contacts, what should I put on there? The manual says to clean the contacts, but nothing about what sort of lubricant to put on after.

Thanks in advance
-Chris

Vgkid · « **Reply #35 on:** November 12, 2015, 11:11:26 pm »

Have you opened up the box, and seeing if anything is binding in the switching mechanism. I doubt that there would be enough grease to foul that up.

PTR_1275 · « **Reply #36 on:** November 12, 2015, 11:41:36 pm »

Yeah, opened the box up and the contacts didn't look too bad. I think it is in the shaft of the switch itself rather than the contacts being gunked up. If I'm going to spray a lubricant in there I don't want to mess anything up or risk getting it into the wrong places.

Do you know how easy it is to disassemble the shafts? I see some Allan key grub screws around the top part that the ball bearing is against.

I wouldn't mind getting the knobs off the box to give it a thorough clean to remove the dirt on the front panel that has built up over time. I'm guessing that if I get the shaft out, the know goes with it.

plesa · « **Reply #37 on:** November 13, 2015, 12:08:43 am »

I suppose that your GenRad use the same switches like IET HARS series.
For cleaning copper contact I used Deoxit D100 and for protection Kontakt Chemie 61, and for locking mechanism I used Kontakt Chemie WL to remove grease residues.
In user manual they recomended WD40

dacman · « **Reply #38 on:** November 13, 2015, 12:24:44 am »

I would spray LPS-1 down the shafts and on the mechanisms on the bottom. There are a couple of screws on top for each dial and I sometimes will loosen them up to see if the dials will then turn more freely (and try to line up the dials while tightening down the hardware), but the shafts almost always need lubricated if the dials are tough to turn.

PTR_1275 · « **Reply #39 on:** November 13, 2015, 01:40:14 am »

That's giving me a bit more confidence. Do you know how the knobs come off? Spare parts switches don't look like there is anything holding the knob on, but I don't want to go and start prying things off and damaging the box.

How is the best way to clean the contacts without getting gunk all over the resistors or even leaving gunk between the contacts. Would giving it a spray with IPA after the contact cleaner help it make things worse?

Sorry for so many questions, I don't want to damage the box or make things worse, a bit of preventative maintenance now will have the box in good condition for many years.

Vgkid · « **Reply #40 on:** November 13, 2015, 01:53:45 am »

Post up a bunch of pictures(make a thread in the repair section) i dont own a GR box. I want one though.

PTR_1275 · « **Reply #41 on:** November 13, 2015, 02:25:59 am »

Will do. I'll link it in here when I do put one in the repair section so others can find it.

dacman · « **Reply #42 on:** November 13, 2015, 04:21:25 am »

Pop off the gray cap on top. Under the gray cap is a setscrew holding the skirt assembly to a shaft. The shaft goes down through an approximately three inch long bore to the bottom of a Bakelite dial assembly and the shaft is about the same diameter as the bore (therefore there is lots of wall contact area for friction to occur). Solvents like IPA or contact cleaner will freeze up the dial and if used will need to be followed by a lubricant (I use LPS-1). I use LPS-1 on both the shaft and contacts. The only time I use DeoxIT or DeoxIT-Gold is if the unit fails residual resistance. As an alternative, loosen two setscrews on the bottom of the shaft and pull it out from the top, leaving the knob on top attached to the shaft (you may need to knock it out from the bottom).

PTR_1275 · « **Reply #43 on:** November 13, 2015, 04:30:53 am »

Awesome. The gray cap came off and all is revealed how to dismantle them. I wasn't sure if the skirt and knob came off as one. Thank you very much


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Author Topic: EEVblog #461 - Genrad Decade Resistance Box Teardown (Read 20524 times)

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