Hello Everyone, today I just picked up on Facebook Marketplace a Cornell Dubilier Capacitor Analyzer Model BF-50 and I was wondering what the concensus was about those as far as how they compared to the Solar version and the Knight and the Heathkit versions of the Capacitor analyzers?

The one i just bought is going to need to be electrically restored as it currently isn't in working order but it looks pretty straight forward and it looks like its all there, I paid $50 plus shipping for it so I don't know if that was a good price or not, but it seems like a pretty good deal to me compared to how much I've seen working Knight and Heathkit ones going for on eBay.

Any information would be appreciated.

Also how common or uncommon are 12A7 rectifier tubes? I'm curious because that's what this capacitor checker uses and its missing that tube.

I picked one up local a few years ago that I still have to get around to recapping. Even with all the tired caps I was still able to get it to work to some extent.
Quality wise it's excellent. The solid wooden cabinet is all nice and solid,
The push buttons selectors are very well built.

It'll test anything a Heathkit, Solar, Knight will do. As much as I like the Heathkit C3 I would say it's built far better.

You'll also have to do a recap on yours. It doesn't look too bad to do theres a few old dry electolytics in there for filters and a bunch of wax paper caps

Here's a manual I found for them.
hallmanlabs.com/wp-content/uploads/2018/04/cornell-dubilier-bf50-owners-manual.pdf


The 12A7 is 10 bucks or less if you shop around.

I picked one up local a few years ago that I still have to get around to recapping. Even with all the tired caps I was still able to get it to work to some extent.
Quality wise it's excellent. The solid wooden cabinet is all nice and solid,
The push buttons selectors are very well built.

It'll test anything a Heathkit, Solar, Knight will do. As much as I like the Heathkit C3 I would say it's built far better.

You'll also have to do a recap on yours. It doesn't look too bad to do theres a few old dry electolytics in there for filters and a bunch of wax paper caps

Here's a manual I found for them.
hallmanlabs.com/wp-content/uploads/2018/04/cornell-dubilier-bf50-owners-manual.pdf


The 12A7 is 10 bucks or less if you shop around.

Thanks for the info, I think that the reason why the person I bought mine from couldn't get it to power on was because the 12A7 tube is missing.

the one I bought is missing its original leather handle but I think I could make a new one fairly easily with some leather from a local craft shop.

I picked one up local a few years ago that I still have to get around to recapping. Even with all the tired caps I was still able to get it to work to some extent.
Quality wise it's excellent. The solid wooden cabinet is all nice and solid,
The push buttons selectors are very well built.

It'll test anything a Heathkit, Solar, Knight will do. As much as I like the Heathkit C3 I would say it's built far better.

You'll also have to do a recap on yours. It doesn't look too bad to do theres a few old dry electolytics in there for filters and a bunch of wax paper caps

Here's a manual I found for them.
hallmanlabs.com/wp-content/uploads/2018/04/cornell-dubilier-bf50-owners-manual.pdf


The 12A7 is 10 bucks or less if you shop around.

That baby came over on the Mayflower.:D
The 12A7 is a rectifier and low power output penthode. I have one!

That baby came over on the Mayflower.:D
The 12A7 is a rectifier and low power output penthode. I have one!

Nice! Yes I saw the copyright date on the manual for the unit, 1938! :scratch2:

Yeah having no 12A7 would stop it dead in it's tracks. One half of it is the rectifier, and the other half is the amp.

The inside of yours is identical to how I remember mine right down to the blue electrolytics.

Yeah having no 12A7 would stop it dead in it's tracks. One half of it is the rectifier, and the other half is the amp.

The inside of yours is identical to how I remember mine right down to the blue electrolytics.

That's a good sign, that means it hasn't been fiddled around with much over the years. I ordered a 12A7 earlier today, so it should be here by Friday hopefully.

That's a good sign, that means it hasn't been fiddled around with much over the years. I ordered a 12A7 earlier today, so it should be here by Friday hopefully.

The only thing that does look a bit out of place is the big green power resistor that is below the push button switches.
https://i.postimg.cc/pLM0G0SD/Screenshot-2022-01-10-22-54-01-1.png (https://postimages.org/)
Looks like it was changed. Seems kind of strange that there's no spaghetti and such long bare leads traveling across a metal switch.
Otherwise everthing looks the same as how I remember mine.

There's a big wax paper in there that need to be accurate. 2.4 mfd. 60 v. This is part of the bridge capacitors for comparing your cap under test in that range.

The only thing that does look a bit out of place is the big green power resistor that is below the push button switches.
https://i.postimg.cc/pLM0G0SD/Screenshot-2022-01-10-22-54-01-1.png (https://postimages.org/)
Looks like it was changed. Seems kind of strange that there's no spaghetti and such long bare leads traveling across a metal switch.
Otherwise everthing looks the same as how I remember mine.

There's a big wax paper in there that need to be accurate. 2.4 mfd. 60 v. This is part of the bridge capacitors for comparing your cap under test in that range.

I'll check into that when it arrives. It was just mailed out, so it should be coming hopefully the same day as the tube.

Is that resistor supposed to be there?

As for the 2.4 uF 60 V cap, I saw that in the parts list in the manual you sent me, and I was trying to figure out if that was a paper or an electrolytic cap, apparently it's a paper cap by the sounds of it.

Does value of the replacement cap for the 2.4 uF 60 V cap have to be exactly the same as the original? I'm asking because I know that that exact value isn't made anymore, because 2.2 uF is a more common replacement value today.

There's a few highter wattage resistors in the circuit so it's likely suppost to be there. I just find how it's installed to be sloppy and not likely original.


All you'll need to do is parallel a 0.2 along with the 2.2 or whatever combination to get 2.4 mfd. The 2.4 mfd is one of the caps used for bridge reference and if it's off the dial will be off.

There's a few highter wattage resistors in the circuit so it's likely suppost to be there. I just find how it's installed to be sloppy and not likely original.


All you'll need to do is parallel a 0.2 along with the 2.2 or whatever combination to get 2.4 mfd. The 2.4 mfd is one of the caps used for bridge reference and if it's off the dial will be off.

Should I use a regular film/mylar cap in the 2.4 uF 60 V cap position or would a NP electrolytic work there? Just wondering.

Should I use a regular film/mylar cap in the 2.4 uF 60 V cap position or would a NP electrolytic work there? Just wondering.
I don't know how a NP electolytic would work and you'd likely only be able to get 2.2 mfd and have to mix and match to make up the difference. You could try it. Myself I would stick to a film caps. Heathkit used big war surplus oil filled caps for this capacitor on the old model C1 condenser checkers.

I don't know how a NP electolytic would work and you'd likely only be able to get 2.2 mfd and have to mix and match to make up the difference. You could try it. Myself I would stick to a film caps. Heathkit used big war surplus oil filled caps for this capacitor on the old model C1 condenser checkers.

I'll just see what I can come up with.

I don't know how a NP electolytic would work and you'd likely only be able to get 2.2 mfd and have to mix and match to make up the difference. You could try it. Myself I would stick to a film caps. Heathkit used big war surplus oil filled caps for this capacitor on the old model C1 condenser checkers.
I looked up the schematic for the Heath-kit C-1.
It's dated 1948! I think Heath-kit would've never survived without those war-surplus parts and tubes. A 12A6 for a rectifier? They used them in a few kits as both a rectifier and an output tube. :D

I looked up the schematic for the Heath-kit C-1.
It's dated 1948! I think Heath-kit would've never survived without those war-surplus parts and tubes. A 12A6 for a rectifier? They used them in a few kits as both a rectifier and an output tube. :D

Lol yeah. I forgot how they used the 12A6 as a rectifier. Just wire the grids to the plate and you're good to go. Come to think of it I think my tubes have JAN numbers on them. Those war surplus part must have gave Heathkit quite a edge allowing them to sell kits for far less than assembled equipment.

I loved mine till the transformer got some shorted turns between the some of the secondary windings and fried the wire wound pot for the main control. I still need to get around to rewinding the transformer. When it was working it was very accurate for both caps and resistors.

They must have got one sweet deal on all those post war parts. Might explain all the chicken head knobs on the equipment too. I wonder if the early scopes were running war surplus CRT tubes.....

Lol yeah. I forgot how they used the 12A6 as a rectifier. Just wire the grids to the plate and you're good to go. Come to think of it I think my tubes have JAN numbers on them. Those war surplus part must have gave Heathkit quite a edge allowing them to sell kits for far less than assembled equipment.

I loved mine till the transformer got some shorted turns between the some of the secondary windings and fried the wire wound pot for the main control. I still need to get around to rewinding the transformer. When it was working it was very accurate for both caps and resistors.

They must have got one sweet deal on all those post war parts. Might explain all the chicken head knobs on the equipment too. I wonder if the early scopes were running war surplus CRT tubes.....

All the caps used in this cap checker are capacitors I have in my stash the only capacitor I'm worried about being able to get is a .00112 uF cap that's in the 12A7 circuit somewhere, is that one a critical value or can that one just be replaced with a regular .001 uF cap and just be done with it?

Yeah that's a tricky on to get. It'll be a mix and match of .01 and a .0015 to get it.
You've got the value incorrect. It's .0115 MFD 2% 200 VOLT

I was checking through my caps and it's going to be a crapshoot of selecting caps that are that close, and I have to question how accurate my capacity meter is on my DMM getting that close of detail.

It's inportant to get it as accurate as possible as it is used in the bridge and I believe this is used on the low side of the scale for measuring small caps.

Yeah that's a tricky on to get. It'll be a mix and match of .01 and a .0015 to get it.
You've got the value incorrect. It's .0115 MFD 2% 200 VOLT

I was checking through my caps and it's going to be a crapshoot of selecting caps that are that close, and I have to question how accurate my capacity meter is on my DMM getting that close of detail.

It's inportant to get it as accurate as possible as it is used in the bridge and I believe this is used on the low side of the scale for measuring small caps.

Ok, yeah sorry, I was trying to remember the value off the top of my head as I didn't have the schematic in front of me at the moment, but either way, that's still going to be a tricky capacitor to replicate.

I'm assuming that the voltage of the capacitors doesn't matter in this case and I could go with 630 V capacitors and it would be fine, just the capacitance is what matters?

I think you're good with anything above around 50 volt.

I think you're good with anything above around 50 volt.

that's what I figured but I wanted to be on the safe side and ask anyways because I didn't want to mess up the accuracy of the device.

I got my capacitor checker in the mail today, and it was packed really well, they even wrapped the box in paper just like how they used to do it years ago!

This sucker is much bigger than it looks in the pictures (and its heavy!)

this thing from what I can see looks like its never been touched except for that old power resistor and an unmarked capacitor, all of the rest of the capacitors in this thing are the original Cornell-Dubilier capacitors.

The control panel on this unit has a couple of patent dates from 1931 on it. :scratch2:

the rivets that held the control panel plate to the rear cover plate were all sheared off, so I'm gonna have to re-pop rivet the control panel board to the back cover and grind the rivet heads flush like the originals were.

Some of these capacitors are going to be tricky to get to unfortunately and its kind of cramped inside this thing.

The mysterious 21377 part, which looks like a capacitor:

https://antiqueradios.com/forums/viewtopic.php?f=8&t=357126

:scratch2: jr

The mysterious 21377 part, which looks like a capacitor:

https://antiqueradios.com/forums/viewtopic.php?f=8&t=357126

:scratch2: jr

Ok, so it looks to be a flasher device of some sort...:scratch2:

I'll leave that part alone. :thmbsp: :yes:

Well I checked the original 6E5 Tube (it was a coke bottle style tube) and it was a dud. :sigh:

I also found a little black sheet metal shield looking thing inside the cabinet and I was wondering if it was supposed to be some sort of adaptor for the eye tube to adapt the eye tube opening to one of those slender non-coke bottle looking eye tubes. :scratch2:

OK, so the 2.4 uF cap (C1) in this unit is listed as an AC voltage capacitor, is that correct or is that a typo in the manual?
I'm asking because there are no capacitors listed in mouser or digikey that's an AC rated cap at that value (no 2.4 uF 60 VAC caps.)

OK so an update, I removed the original 2.4 uF Cap from the unit and it looks like what they did at the factory was used a 2 uF 60 VAC capacitor in parallel with a .4 uF 600 VDC capacitor to come up with the 2.4 uF 60 VAC capacitor, which I ended up having to do something similar which was order a 2.2 uF 63 VAC (100 VDC) capacitor and then a .22 MFD 630 VDC capacitor which will be paralleled to come up with the 2.4 uF cap I will need.

unfortunately the .12 uF cap is turning out to be a tricky capacitor to locate (they list it as a capacitor that is available at Mouser but its not one that they keep in stock and the factory lead time is 22 weeks.)

OK, so that green resistor you guys thought looked out of place and looked like it might of been replaced, its original to the unit, its R12 on the schematic for this unit, its the 15K ohm 5W WW resistor that bridges between switch 6 and 7 on the leakage test button panel, and it does actually have spaghetti sleeving on it, its really dark brown colored which is why it doesn't look like its got any on the leads in the picture.

OK, so I was checking out the capacitors a little more closely in this unit and there are 4 mica capacitors that are not marked and I'm not sure what those are supposed to be, I was wondering if the 4 mica capacitors isn't the .0115 MFD capacitor, because otherwise I don't see any caps marked with the value .0115 MFD in this unit. :scratch2:

Also there seems to be some capacitors in this unit that aren't listed in the parts list/schematic for this unit, such as a second .12 MFD 400 VDC capacitor and a second .4 MFD 600 VDC capacitor (the first one was part of the 2.4 MFD 60 VAC capacitor.)

Any ideas as to what those caps might be all about? :scratch2:

UPDATE: I figured out what the second .4 uF 600V capacitor was from, it was replacement for the second .5 uF 600V Capacitor that was in the unit, (which I was wondering why there didn't seem to be a second .5 uF 600V cap in the unit.)

Also I noticed that there was quite a bit of shoddy repair work done on this unit in the past (this was apparently owned by the US Government at one point in time as the case was etched twice with marks stating US-H920M and then OE-1968, and whoever was doing the maintenance on this device for whatever Government agency that owned this did quick and sloppy work, basically just did whatever they had to to keep it going), so I corrected a lot of shoddy repair work including relocating that green power resistor (which was original to the unit as it had the same part number listed as the manual listed for that particular part) so that it was going down along the bottom side of the switch array rather than the back of the switch array like it was previously.

OK so I have a question about this unit, since the original 6E5 tube was DOA (open filiment) I'm going to have to replace the original 6E5 tube with another eye tube and the only semi functional eye tubes I've got (that produces a bright green glow) is a 6N5 and a couple of 6U5/6G5 tubes and the 6N5 eye tube I have is the brightest of all of the eye tubes I have.

My question is, could I use a 6N5 eye tube in this unit and this unit still work?

Any help with this matter would be appreciated. :scratch2:

OK So I got the capacitor checker up and running finally, unfortunately my eye tubes I have are not very bright so I have to have the lights off overhead in order to see anything.

Any ideas as to what that black sheet metal shroud thing is that I was referring to in an earlier posting?
See attached picture below.

Also it seems like the flasher module (the C-D Part No. 21377) isn't working because when I was going through the various capacitor tests that are supposed to utilize that section (leakage tests) the eye tube didn't flash, and I was using really old paper caps that I would of thought would of triggered that function. :scratch2:

Also was this thing supposed to have test probe leads? I'm asking because there are standard sized banana plug inputs on the control panel that accept standard size banana plugs, and this thing didn't have any test leads with it when I got it.

Any help with this would be appreciated.

Mine has alligator clips and banana plugs. Leads are about 2 foot long.

I think the shroud is someones add on, mine doesn't have one.


Edit. I seen the pics Yeah I also think this is a capacitor. No clue on the ratings though. If I recall, when it's working the eye will open and close if there's leakage. If the leakage is slight it would pulse once every second or so, and if it was very leaky it would pulse rapidly. I think mine was working on the leakage test. It's a shame I don't have it in front of me or I would take some measurments off it.

Heathkit's early C1 and C2 testers had much the same idea using a neon bulb.

Mine has alligator clips and banana plugs. Leads are about 2 foot long.

I think the shroud is someones add on, mine doesn't have one.


Edit. I seen the pics Yeah I also think this is a capacitor. No clue on the ratings though. If I recall, when it's working the eye will open and close if there's leakage. If the leakage is slight it would pulse once every second or so, and if it was very leaky it would pulse rapidly. I think mine was working on the leakage test. It's a shame I don't have it in front of me or I would take some measurments off it.

Heathkit's early C1 and C2 testers had much the same idea using a neon bulb.

Ok, thanks, I'll just have to make up some of my own test leads using hookup wire, a couple of banana plugs and some alligator clips.

As for the C-D Part 21377, according to a thread on the ARF that Jr. had posted a link to in here, they were saying that that part was some sort of flasher module that utilized a neon bulb or some sort of gas discharge tube assembly that had to be sealed in a dark tube because of it being a "light dependent" circuit, but the person that was explaining that on there had admitted that it was just a guess on his part since the service/owners manual doesn't give any additional information about that part other than a part number, making me wonder if it wasn't some sort of proprietary part that Cornell-Dubilier didn't want others to duplicate.:scratch2:

You'd think if it was a cap that they would have just listed it, but they kept it kind of cryptic as to what it is, and don't have it listed on the parts list for resistors and capacitors, just on the schematic.

I'm trying to remember how mine worked on leakage and it seemed like the eye flashed open and closed. If this was the case, a gas discharge tube, or a neon bulb would make sense.

You'd think if it was a cap that they would have just listed it, but they kept it kind of cryptic as to what it is, and don't have it listed on the parts list for resistors and capacitors, just on the schematic.

I'm trying to remember how mine worked on leakage and it seemed like the eye flashed open and closed. If this was the case, a gas discharge tube, or a neon bulb would make sense.

I'm guessing that's what it is, because like I said the ARF forum thread linked to here by Jr. suggested that might of been what it was.

But like I said when I was testing some capacitors I had on hand (including some of the ones I took out of the cap checker itself) it didn't seem like it was working like it should of...:scratch2:

Although like I said, it doesn't help matters any that my selection of eye tubes I have on hand are crap (they are very weak and don't glow very bright and aren't very responsive.)

I was able to source from a friend of mine (a fellow antique radio collector who lives locally) a NOS 6E5 Eye Tube for my capacitor checker and now its working as it should.
I checked several capacitors (new and old ones) and the cap checker worked just like its supposed to. :thmbsp: :banana:

Right on glad it's working. Was I correct that the eye flashes with leakage?

Right on glad it's working. Was I correct that the eye flashes with leakage?

Yes it does, but not a flash like in the sense of like flashing Christmas lights, but more like the eye tube flashes open and shut depending on how much leakage there is.

That's what I remember mine doing too. Glad you got it going.
I'll have to ge mine going. I should have all the caps to replace the wax papers now, and I think I've got enough Electrolytics on hand.

Yes, I actually used it to get my Zenith Trans-Oceanic Radio recapped and I also used it to help recap my 1935 GE, it turns out that the capacitors in my Trans-Oceanic while they were "bumblebee" caps the majority of them were still good yet, none of them measured shorted and measured very little leakage. There was one cap that measured "shorted" (eye tube stayed open) and that was the capacitor going between the cathode of the 1L6 tube to ground (cathode bypass cap) which would explain why my radio liked to fade in and out sometimes with distant stations, seeing as the 1L6 tube is the RF Amplifier tube and if anything electrical related to that goes bonkers then your radio usually starts fading in and out.