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  #16  
Old 05-09-2014, 08:49 AM
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NoPegs NoPegs is offline
The glass is -3dB.
 
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Informational update. I consulted another matriarch of things woodworking and until I can get her some images of the unfinished interiors and/or endgrain structure her best guess is something along the lines of Norway Maple...

http://www.wood-database.com/lumber-.../norway-maple/

Goes to show that being from the northeast most of the maple I see doesn't look anything at all like that when sawn...

My brain thinks of this as "maple"

http://www.wood-database.com/lumber-...ds/hard-maple/
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  #17  
Old 05-10-2014, 08:49 AM
powerking powerking is offline
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Regarding the Canned-ohm resistor network, I replaced mine with 5 7.5-Kohm 5% 3w metal oxide resistors arranged on a terminal strip w/teflon tubing on the leads. This is 50% more power rating than the origninal (~~ 7.5W dissapation on the Canned-ohm network). Math of 500V accross the network comes out to about 7.5W. From the schematic, to me that is all this piece of the circuit is used for; the capacitor leakage test voltage accross the cap being tested; nothing else. When I measured each of the sections of the Canned-ohm one, they were not exactly "close" to each other; hence why I replaced it per the above.


Tom (PK)
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  #18  
Old 05-10-2014, 11:17 AM
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Looks to me that the resistor network also supplies the plate bias for the eye-tube.
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  #19  
Old 05-11-2014, 09:58 PM
powerking powerking is offline
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Yup, I mis-spoke about the leakage resistor network. It does supply the ~~ 200Vdc to the 6E5 tube (tap off the position #2 of the leakage/selector switch and where the other 8uF cap filters it too)..; my bad...

Tom (PK)
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  #20  
Old 05-12-2014, 06:41 AM
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NoPegs NoPegs is offline
The glass is -3dB.
 
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Quote:
Originally Posted by powerking View Post
Regarding the Canned-ohm resistor network, I replaced mine with 5 7.5-Kohm 5% 3w metal oxide resistors arranged on a terminal strip w/teflon tubing on the leads. This is 50% more power rating than the origninal (~~ 7.5W dissapation on the Canned-ohm network). Math of 500V accross the network comes out to about 7.5W. From the schematic, to me that is all this piece of the circuit is used for; the capacitor leakage test voltage accross the cap being tested; nothing else. When I measured each of the sections of the Canned-ohm one, they were not exactly "close" to each other; hence why I replaced it per the above.


Tom (PK)
Quote:
Originally Posted by Notimetolooz View Post
Looks to me that the resistor network also supplies the plate bias for the eye-tube.
Hmm, I'll play it by ear when it arrives. I know eye tubes can be finnicky, but usually its the 1meg between the plates that screws them up. I'm hoping my can of ohms hasn't leaked and this is all just undue worrying on my part.

Quote:
Originally Posted by powerking View Post
Yup, I mis-spoke about the leakage resistor network. It does supply the ~~ 200Vdc to the 6E5 tube (tap off the position #2 of the leakage/selector switch and where the other 8uF cap filters it too)..; my bad...

Tom (PK)
Edit: Disregard this. I have brought shame upon my house by screwing up Ohm's Law in public.

I think your math is a bit off there, 500v into ~36k is, indeed, just under 7W on a good day, however if you replaced them with 3w metal film resistors, you're in for a potential smoke scenario, because they're in series. Still only rated for 3W.

(I bet you mistyped it, or maybe your rectifier is just that far gone that it can't stump up the full 14mA for some reason.)


In related news my CB-1 is now within 50 miles of my door. Will it get here today? I hope so. Will it make very sad noises when I pick it up? I really hope not.

Last edited by NoPegs; 05-12-2014 at 08:07 AM. Reason: I broke Ohm's Law. :(
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  #21  
Old 05-12-2014, 07:01 AM
powerking powerking is offline
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NoPegs,

My math should be correct. The original Canned-Ohm resistor sees a TOTAL power dissapation of ~~ 7.5W. Therefore if you put 5 7.5K-ohm 3W resistors in series they are each dissapating about 1.3W @500V end-to-end. And I used metal oxide 5% ones, not metal film (not that critical for the leakage tests).


Tom (PK)
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  #22  
Old 05-12-2014, 07:56 AM
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The glass is -3dB.
 
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Quote:
Originally Posted by powerking View Post
NoPegs,

My math should be correct. The original Canned-Ohm resistor sees a TOTAL power dissapation of ~~ 7.5W. Therefore if you put 5 7.5K-ohm 3W resistors in series they are each dissapating about 1.3W @500V end-to-end. And I used metal oxide 5% ones, not metal film (not that critical for the leakage tests).


Tom (PK)
Argh! You're right. "100v each" at 13.4mA is 1.34W... Next thing I know I'll screw up my zip-code!

At least if I screwed this up in the past my error was on the safe side of the equation instead of coming up short(ed).
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  #23  
Old 05-13-2014, 10:14 AM
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The glass is -3dB.
 
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It has arrived...

Allrighty! I was surprised to find that the seller did an excellent job of packing it. I had asked to put something firm but squishy between the lid and the dial plate, because in the pictures he listed with it, there were no screws holding the face on. Strangely it arrived with 9 out of 10 screws installed, and the 10th one was discovered inside the cabinet.

I did some quick poking after unboxing it yesterday (Working 3rd shift is a bummer, didn't get delivered until almost 1400, I stayed up for it.) just to get a feel for it. I think the segment of my candohm furthest from the chassis connection is open, but I only grabbed the DMM out of my go-bag to check, and the probes it has are kind of dull and awkward so I'll be double checking that in the next day or so.

The good news seems to be that all windings on the power transformer have what appear to be valid readings of resistance. The main potentiometer also checks out in both overall value and linearity. Bonus points awarded because the mechanical action is nice and smooth too.

My "goat" shields are unpainted and kind of corroded, so I have to figure out how best to polish them up without flattening them out in the process.

There is rust inside, but not anything serious. Going to get a new pot of naval jelly if it doesn't come right off with some steel wool and cutting oil.

I'll see about taking some decently composed pictures, but that might not happen till the weekend.

My initial thoughts are "Well, it turns out to be smaller than my breadbox." I knew they were smaller in person, but when I sent the better half a quick cell pic of it next to my previously mentioned breadbox for scale, she commented on how "cute, but intelligently cute." it is. I quite like it myself, but its good that she approves.


Were the front plates lacquered/shellaced/varnished? Mine has a strong brown tint to it. I prodded it with some denatured alcohol and it comes off, nice and shiny underneath. I honestly can't tell if it's aged shellac or decades of tobacco smoke tar. I just gave it another eyeballing and the inside of the lid has some "condensate" on it. This could be from being stored in a hot attic for years with the lid closed. Baked the shellac off the wood. Might have solved that mystery myself just now.

After stripping the goats off the tubes, it looks like at some point in the past someone "cleaned" the tubes. Neither have markings that I can reveal with any of the usual voodoo. (I haven't tried gold sputtering, although I do have a stash of gold leaf on hand, *mad science cackle*) Obviously the eye-tube is an eye tube. The rectifier is a UX-4 base so probably a 1V, but I can't be certain due to the absence of markings. It's a Sylvania with the really, really old logo. Definitely a rectifier from the internal construction.

I'll admit to only having an emissions type tester, Accurate Instruments Co 257. No UX-4 or UX-6 sockets, and I know I can't make the eye tube do anything with the voltages it supplies, but if I break out the pins and connect the 1V up, 6.3v filament, and test it like one side of a 5U4 or 6X5 (Which I can test with my unit.) I can confirm that it hasn't failed, without blowing it up in the process, right? (After my epic failure at Ohm's law yesterday, I'm kind of spooked now.)

Filaments are good on both tubes, hoping I lucked into a low-hours eye-tube in the process, but I won't know that for a while.

I'll ask the wood ladies what their final answers are, after I take some better lit pictures. The good news is whatever wood it is constructed out of, replicating it will be a trivial task, so you need not remain sans-cabinet much longer, drdave3!

I may end up just lightly steaming mine so it deconstructs, trace out the panels and then glue it up nice and solidly again. It's just a wee bit loose as it sits. I have to think about that.

Has anyone tried to calibrate one of these things? I mean just improving the overall accuracy, not anything excessive like you'd do for a scope or VTVM... Seems to be a calibration pot inside, and the manual mentions factory re-calibration. I'll take any tips I can before pushing into new territory and experimenting myself.


Wow, apologies to anyone who's still reading after the wall of text up there. Thank you!
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  #24  
Old 05-13-2014, 11:21 AM
powerking powerking is offline
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The hardware and hinges were nickle plated steel. I cleaned mine up using the ultra-sonic cleaner with Birchwood-Casey case cleaner solution. Then used the Dremel tool with a felt buff w/jeweler's rouge. Then totally clean them with acetone and paint with clear lacquor. I had researched some "home" nickel plating products but decided this was too much money for the desired end results. I'll post pictures of the final "product" forthcoming.

Tom (PK)
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  #25  
Old 05-13-2014, 11:48 AM
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NoPegs NoPegs is offline
The glass is -3dB.
 
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Quote:
Originally Posted by powerking View Post
The hardware and hinges were nickle plated steel. I cleaned mine up using the ultra-sonic cleaner with Birchwood-Casey case cleaner solution. Then used the Dremel tool with a felt buff w/jeweler's rouge. Then totally clean them with acetone and paint with clear lacquor. I had researched some "home" nickel plating products but decided this was too much money for the desired end results. I'll post pictures of the final "product" forthcoming.

Tom (PK)
Ask your local gunsmiths if they could get them plated for you with their next batch of bits they send out... I bet you're pleasantly surprised with both the results, and the "cost" of tagging along...

I'm looking at mine now and I never would have thought "Hmm, this was nickel plated." Makes sense now that you point it out, though.
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  #26  
Old 05-13-2014, 02:50 PM
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Might want to watch the filament voltage when you test the 1V. Some testers depend on the filament current to load the filament supply to the right voltage. I don't know the filament current specks of the 1V so this might be an unimportant point.
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  #27  
Old 05-14-2014, 05:29 AM
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NoPegs NoPegs is offline
The glass is -3dB.
 
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Originally Posted by Electronic M View Post
Might want to watch the filament voltage when you test the 1V. Some testers depend on the filament current to load the filament supply to the right voltage. I don't know the filament current specks of the 1V so this might be an unimportant point.
You raise a valid point. Sadly in my case my unit is just a tapped autotransformer, I have 1.4, 3.0, 5.0, 6.3, 12.6, 25, 50, and 115v filament voltage positions. Now I do have about 127 volts average (Did you know you can buy actual 130v incandescent lightbulbs? I learned that real quick after moving in here and going through too many normal bulbs in the first 3 months.) so I do use my variac when possible. Otherwise I warm a tube up on the next lower setting for 2-3 mins and if it tests marginal I'll bump it up to the listed position and see if it makes a difference. So far everything that tested marginal on the lower setting hasn't improved on the "listed" setting at 10% overvoltage average.

Now for something like a 35Z5 it lists the 25v tap position, so I don't bother warming it up on 12.6 because I'm still short 10v or so at the listed position. Some day I'll acquire an actual tube tester with lots of levers... Someday...


Related morning thought: 115v position, Was that really a common filament rating at some point in the 60s? It does have compactron sockets, and if anything was nutty enough to use a 115v filament (That wasn't a rectifier.) it'd have to be a compactron...
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  #28  
Old 05-14-2014, 01:09 PM
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Quote:
Originally Posted by NoPegs View Post
Has anyone tried to calibrate one of these things? I mean just improving the overall accuracy, not anything excessive like you'd do for a scope or VTVM... Seems to be a calibration pot inside, and the manual mentions factory re-calibration. I'll take any tips I can before pushing into new territory and experimenting myself.
From my experience with a Heathkit cap tester and looking at the CB-1-60 schematic, if there is a pot inside it isn't stock.
The only stock calibration on the Heathkit involved loosening the dial shaft lockscrew while measuring a know capacitor and moving the dial until it shows the correct value. I would use a value near the middle of the middle range. I ordered a 5% cap from Mouser (or was it Digi-Key?). If the other cap ranges are then off then the bridge reference cap value(s) would need to be changed. If you are going to re-cap the bridge cap I would use 5% anyway.
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  #29  
Old 05-14-2014, 01:16 PM
powerking powerking is offline
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Agreed,

There is/was no calibration inside the CB-1-60 other than the position of dial knobs on the P.F. and main R/C pots. Regarding the resistors and precision caps in the Wien bridge; I went with 1% metal film & polyester types for best performance/accuracy.

Tom (PK)
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  #30  
Old 05-14-2014, 04:22 PM
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Quote:
Originally Posted by NoPegs View Post
Related morning thought: 115v position, Was that really a common filament rating at some point in the 60s? It does have compactron sockets, and if anything was nutty enough to use a 115v filament (That wasn't a rectifier.) it'd have to be a compactron...
I don't know of any compactrons that have a filament voltage above 40V.

There was an octal 117L7 (?) that contained a rectifier and a power pentode that was made for '1 tube wonder' phonographs before selenium rectifiers became common in cheap phonos.
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