#31
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Allrighty! Providing the last of the components arrive in time, I'm planning on using the 3-day weekend to overhaul my unit. Expect updates then!
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#32
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The 58HE7 and 53HK7 HOT/Dampers are the only ones that come to mind.
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#33
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Just curious on the overhaul project; are you going to do a total re-cap, re-resistor, and re-wire job on this unit? To me, once I unsolder a component in a tester like this one's 70 year old vintage, then "it" gets replaced; even the oldy/mouldy cloth covered wiring. About the only things I kept on mine were the "hard" parts including the still V.G.C. terminal strips. To me "soft parts" include inferior/old style aged and designed caps, carbon comp & some wire wound resistors, cloth/tar wiring, rubber grommets, etc.
Tom (PK) Last edited by powerking; 05-21-2014 at 04:31 PM. |
#34
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Quote:
My current plan is to replace most of the caps, (I ordered replacements for them all, but I'm going to leave the existing mica in there (C3) as it tests at 190pf with a DMM, should be 200pf.) bridge in a leg to bypass the open section (R7) of my candohm, and slap a new line cord on for evaluation purposes and then test it. I bought a few high precision caps, basically 1, 3, and 5 on the scale (so about 25%, 50% and 75% rotation wise on the knob) of all 3 ranges and I'll see how it performs. My thoughts are that the knob might have been "calibrated" with the mica at 190pf. I plan to take the knob off and lift the dial plate out so I can remove any rust between it and the actual steel chassis it hides, but I want to ballpark it with the knob as it has been for many decades first. I'm planning to go poke the resistors associated with the eye-tube this morning, and see if I should replace them right off too. (The 1 meg on eye tubes "usually" is way off, we'll see how mine is.) Edit: The 10 meg is 12.17 megs (so 22% off) and surprisingly the 1 meg is 1.08 so 8% off. I'll sack them both in the first barrage... Basically the only discrete parts I didn't order up are the R1 and R2 precision resistors. For two reasons. First: I'm not sure what the wattage needs to be. Second: I'm not intending to use the resistance functions of the unit, because a DMM can do that with orders of magnitude more accuracy and not deplete the life of my eye-tube in the process. Mine also seem to be well within 2% when I measured them so it might function within spec on the old resistors anyway. The wiring in mine seems to be in fine condition, if it was the early rubber covered type and brittle I would probably re-weave the wires. I picked up a tube of Simichrome at the awesome local hardware store that's over 100 years old and usually has "everything" if you look hard enough, and I'm thinking I can bring my "Goats" back to a shiny life with it. Cotton or Microfiber? I'm thinking cotton because the MF will probably just trap the Simichrome in the fibers instead of rubbing it on the corrosion... They're coming! Soooooooon! Last edited by NoPegs; 05-22-2014 at 06:21 AM. Reason: Values acquired! |
#35
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Where did you find the precision caps?
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Audiokarma |
#36
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More or less I just drilled down in the parametric search on mouser, but there's a bunch of 1% 500V units.
Basically drill it down as package type, so radial and axial, pick a voltage, then poke what precisions are available in your desired value range... http://www.mouser.com/Passive-Compon...z0wljoZ1z0z7l5 If you mean where did I find the precision caps used in the bridge itself, here's what I got. http://www.mouser.com/Search/Product...67-ECW-F4205HL http://www.mouser.com/Search/Product...2222-419-72004 http://www.mouser.com/Search/Product...-CD15FD201FO3F Yeah, the big one is 3%, I couldn't find a suitable 2% that was both in stock and < $10. When I have a bit more money to toss around I'll look into it. Not like it's any major job to open it up and upgrade precision, 10 mins, tops. Package is out for delivery! Hopefully before 1400... |
#37
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It lives!
https://www.youtube.com/watch?v=1lpLAjZMj90
IT LIVES! My can of ohms got really really weird when we unmounted one end to pop in a terminal strip, so the original plan of just fix the last segment being open turned into the full "pull it out and re-make it." In the future I'm going to go back and re-dress the wires and generally make it look a bit less of a lash-up, but it functions! |
#38
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Well,
I wouldn't rate your "restoration" efforts so far as grade "A" seeing these photo's. But then again you said this was a first pass with the new parts. I'd like to see the finished product. Tom (PK) |
#39
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C- on aesthetics. B on functionality. The night we planned to do the quick resto became significantly more complicated once the candohm decided to flake out and we had to do major surgery to replace it. I had planned on the first pass to be just add a 7.5k resistor in place of the open section at the end, swap the caps, and fire it up. We wound up replacing the bias resistors, and having to reconfigure the wiring with what little I had handy at the time. The patient lived, but is horribly disfigured... I've been a bit... distracted... lately. Pictures shortly as to why. (Spoiler: Rigol.) I have grand plans for my CB-1-60. Soon it shall become the CB-1-60 Mk II. With any luck it will survive another 60+ years. (Yes, I'm honor-bound to remain true to the original design. I'm making some slight modifications, but by means are we talking paint or transistors. There might be a diode involved, I haven't quite decided on that bit.) |
#40
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Here's a bit of a teaser since I've had some time to work on my plans with the holiday and all...
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Audiokarma |
#41
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Quote:
After you place your components, you simply connect the "dots" with virtual wiring and flip a virtual toggle switch on and virtually see what your design will do with virtual meters for R, I, E, and even a P meter! Oh, and a scope to boot! Anyway, well worth it if you are into circuit design and presentation. Maybe my teachers and professors were too picky.......
__________________
"Face piles of trials with smiles, for it riles them to believe that you perceive the web they weave, and keep on thinking free" |
#42
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Here's what the schematic looks like (I didn't bother cleaning it up, I just needed it electrically correct and component-correct so that I could lash the whole thing up as a PCB.) There's no spoiler tag option installed here at VK so I have to transmit this in the clear I guess... Hint: Look at the component numbers, and then go look at the CB-1-60 schematic... Here's a teaser that has no airwires pictured and also has the traces on the correct side of the copper for through-hole components. I still need to pop things apart and take some mounting and clearance measurements before I decide the final shape/size of the board and where to place the mounting holes on it. I'm also holding off on designating the isolation slots to be milled out until I revise the layout more based on measurements, but be assured I am taking the fact that there's ~500VDC on this board into account. |
#43
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It looks like there was a "pilot error" in your CAD drawings regarding C6 and C7 and their polarity thereof; (LOL) and magic smoke would result...
http://www.allaboutcircuits.com/vol_1/chpt_13/5.html Also, why all the bother of doing a 21st century PC board when a simple time period correct 8-way terminal strip will do the same function (and terminal strips were how it was done; construction at the time) to somewhat maintain the authenticity of it? How far does one go with a restoration or a total re-engineering of this type of vintage gear? In the 1940's when this unit was produced, man-kind had no idea of how PCB materials like FR-4 would eventually revolutionize the electronic world of construction. Tom (PK) |
#44
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Yep, non-polarized film caps though, I just needed the right package style for pad placement and spacing. (Strangely the board layout icon is non-polarized but the schematic capture icon is...) If it were a polarized package style one of the pads for the caps would be square to indicate polarity. I'll have to play around with some of the other cap options and see what else is "not accurate."
As to why I'm going with a modern PCB style upgrade, the board will evolve over the next few weeks. I'm adding the ability to change the target voltage on the eye tube, and maybe one or two other things, including possibly adding a 1µF to "700"µF range. (700 only because that's the normal scale max of "70" x10, I honestly don't expect accuracy out of it, but I'll see what I can do.) The target voltage taps are for two reasons. First, to preserve the life of any eye tube by running it at a lower voltage that provides adequate brightness. (probably +160). Second, having higher taps (I'll go as high as +260) will allow one to use an already mostly worn out eye tube right down to the final nub of darkness. This considers a future where there are no NOS eye tubes available at any price, all have been used, some a lot more than others. The process of testing these changes will be very ugly, but once a working system has been achieved, boards will be made, components attached, and wiring replaced with some new manufacture cloth-covered wire. The goal is to have an intelligent blend of old and new. |
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