$9 Densitometer

[htmlguru4242]

I love eBay. I picked up this Tobias TBX Densitometer for $9 (yes, nine) USD + shipping. It was listed in poor cosmetic condition, and non-functional. The control panel had fallen off, which was fixed in about 30 seconds with some E6000. Spoiler-alert, it's 100% functional - evidently the fool who sold it failed to notice it was missing a fuse.

Since it was "non-functional" I'd planned on removing the guts and replacing them with an AVR micrcontroller and an I2C lux sensor that I had hanging around. When I got it, I noticed it was missing a fuse, which I replaced with a paperclip (this is dangerous - kids, don't try this at home). A couple of the switches need cleaning, but other than that, it's fully functional.

I'm excited than I can now start with some real sensitometry.

Does anyone have an idea on the age of this thing? Also, the "xmit" function is straightforward, but does anyone know what the "Auto Xmit" function does? I can't find a manual from Tobias, and Mike Butkus doesn't delve into darkroom gear, so I'm a little lost here.

(For the few of y'all who don't know, Mike ( https://butkus.org/chinon/index.html ) has an outstanding library of vintage photo gear manuals, and should be your first stop if you need a manual for old gear. Everything is free, though he does accept donations, which in my opinion are well-deserved. (I have no affiliation with the site whatsoever, I've just made extensive use of it in the past.)

For the technical folks, the electronics inside are computerized, but seriously vintage - a the power supply is all linear with huge filter caps, a Zilog Z8 microcontroller with an external ROM (EEPROM I'm guessing, from the ceramic package and sticker - which I may dump and see the software that makes this thing tick), a bunch of support chips, and some 74LS glue logic - real live TTL stuff. There are a few metal-can packages on the analog board (IDK if they're transistors or op-amps, I didn't tear it down that far). The display board (which has socketed 7 segment displays) looks like it was made in house, because there's no soldermask, and all of the traces are tinned.

A very sad roll of Svema Micrat Orto direct is sitting on top of it; I'm still trying to nail down the correct development chems and times.

 

[koraks]

There are a few metal-can packages on the analog board (IDK if they're transistors or op-amps, I didn't tear it down that far).

Likely mostly the former. Easy enough to count the pins; if there are 7 or so, they're opamps. Back in those days, high performance opamps often came in metal cans.

Nice score!

 

[htmlguru4242]

Likely mostly the former. Easy enough to count the pins; if there are 7 or so, they're opamps. Back in those days, high performance opamps often came in metal cans.

Nice score!

I'd imagine they are as well - I just haven't bothered to tear the whole thing apart and look, since I really don't have a reason to.

 

[koraks]

I can imagine. The unit looks in great shape btw.

 

[Kino]

Nice find, however, if the replacement lamps are anything like those of the Macbeth series, you will pay dearly for a replacement!

Luckily, Tobias is still in business, but I wouldn't wait to grab a replacement bulb if I were you.

 

[albada]

Also, you might want to replace those electrolytic caps. You are probably aware that they dry out.

 

[ic-racer]

Very nice. I have two Tobias TBX I got over 20 years ago. I thought I got a good deal back then, $25 for both. I got the service manual and the matching Wejex sensitometer too. I found them easy to keep running.

Tobias Densitometer Tune Up

I was doing some year-end cleaning and got out my spare densitometer for a checkup. Seems to work OK but the button did not work all the time. Thanks to Mouser's extensive database of switches, I was able to get an exact replacement.

www.photrio.com

 

[htmlguru4242]

Very nice. I have two Tobias TBX I got over 20 years ago. I thought I got a good deal back then, $25 for both. I got the service manual and the matching Wejex sensitometer too. I found them easy to keep running.

Tobias Densitometer Tune Up

I was doing some year-end cleaning and got out my spare densitometer for a checkup. Seems to work OK but the button did not work all the time. Thanks to Mouser's extensive database of switches, I was able to get an exact replacement.

www.photrio.com

Is that one board of ICs all that's in there (other than the PSU board)? If so, they really simplified things from the TBX I have. Or is there another board in there somewhere?

 

[htmlguru4242]

Nice find, however, if the replacement lamps are anything like those of the Macbeth series, you will pay dearly for a replacement!

Luckily, Tobias is still in business, but I wouldn't wait to grab a replacement bulb if I were you.

I've attempted to contact Tobias via phone and e-mail a few times (including before I ordered the unit, to see if there was a manual), and haven't heard back.

Do you know of a secret to getting in touch with them?

Everything from Macbeth / XRite as far as test and process control stuff goes is expensive, for no other reason than ... it can be? I know they're calibrated, and may even be custom production runs of lamps, but $200+ for a lamp? You can't be serious.

 

[Kino]

I've attempted to contact Tobias via phone and e-mail a few times (including before I ordered the unit, to see if there was a manual), and haven't heard back.

Do you know of a secret to getting in touch with them?

Everything from Macbeth / XRite as far as test and process control stuff goes is expensive, for no other reason than ... it can be? I know they're calibrated, and may even be custom production runs of lamps, but $200+ for a lamp? You can't be serious.

No, sorry.

Yeah, the Macbeth/XRite parts are stupid expensive. In the end, if Tobias turns out to be similar, I suggest you check out the Dektronics Printalyzer transmission/reflective densitometer with LED illumination for about the price of ONE Macbeth bulb.

Printalyzer Densitometer — Dektronics

Compact budget-friendly densitometer for anyone who wants to take a more analytical approach to testing black and white photographic film or paper.

www.dektronics.com

I intend to buy one but it's a bit down on the priority list at the moment...

 

[ic-racer]

Is that one board of ICs all that's in there (other than the PSU board)? If so, they really simplified things from the TBX I have. Or is there another board in there somewhere?

There is a third PC board on the side of the enclosure as seen in this diagram. I also want to correct, mine are TCX for color, but I have only ever used them for B&W.
I included a page from the calibration instructions, in case your device calibrates in a similar manner.

 

[htmlguru4242]

No, sorry.

Yeah, the Macbeth/XRite parts are stupid expensive. In the end, if Tobias turns out to be similar, I suggest you check out the Dektronics Printalyzer transmission/reflective densitometer with LED illumination for about the price of ONE Macbeth bulb.

Printalyzer Densitometer — Dektronics

Compact budget-friendly densitometer for anyone who wants to take a more analytical approach to testing black and white photographic film or paper.

www.dektronics.com

I intend to buy one but it's a bit down on the priority list at the moment...

Honestly, if the bulb goes and it's that outrageous to replace, I'm sure I can find a suitable [commodity] lamp and re-calibrate. I know ISO has spectral standards for illumination in densitometry, and it's definitely important for color work, but I can't see it making that much of a difference with B&W films.

 

[Kino]

Honestly, if the bulb goes and it's that outrageous to replace, I'm sure I can find a suitable [commodity] lamp and re-calibrate. I know ISO has spectral standards for illumination in densitometry, and it's definitely important for color work, but I can't see it making that much of a difference with B&W films.

Yes, it's all relative anyway. As long as you are not trying to coordinate between two labs to exacting tolerances, and the unit is stable and repeatable, you are good.

 

[ic-racer]

I do have a spare lamp for my two units which cost over $100 which is not too bad as a new Tobias TCX is over $3000.

 

[htmlguru4242]

I spoke to one of the engineers at Tobias, who said he'd get back to me on the exact cost of the lamp if I wanted, but he knew they were "fairly" expensive.

I had about a 40 minute conversation with him - evidently their former lamp supplier are no longer around, and sourcing lamps with proper specs is nearly impossible with current industry conditions due to the dominance of LEDs. Evidently they attempted to design an LED replacement, but were unable to obtain an adequate spectral match - which is unsurprising.

 

[ic-racer]

I got my spare lamp from Interlight: Sylvania 7P6v. May be the same as in your unit.

 

[htmlguru4242]

I spoke to one of the engineers at Tobias, who said he'd get back to me on the exact cost of the lamp if I wanted, but he knew they were "fairly" expensive.

I had about a 40 minute conversation with him - evidently their former lamp supplier are no longer around, and sourcing lamps with proper specs is nearly impossible with current industry conditions due to the dominance of LEDs. Evidently they attempted to design an LED replacement, but were unable to obtain an adequate spectral match - which is unsurprising.

Did I accidentally strikethrough my post, or did it get moderated? Ha.

 

[koraks]

did it get moderated

Certainly not! I read your post when it just appeared and was puzzled by the strikethrough. In the edit history I can see that it wasn't modified until you fixed the strikethrough thing 14 minutes ago.

 

[htmlguru4242]

Certainly not! I read your post when it just appeared and was puzzled by the strikethrough. In the edit history I can see that it wasn't modified until you fixed the strikethrough thing 14 minutes ago.

Excellent. Thank you!