Jobo 3005 rotation question

[atlcruiser]

Hi All,
I just got my brand spankin new 3005 drum from Greg...great to deal with BTW :) I sold my left kidney.

I planned to used a CPE2+ for this drum. Of course eveyone told me the CPE2+ was too small! I got a heat gun and bent back the edges of the trough and got the drum in there with no real issue.


So, now I have one speed marked 75. I am guessing this is 75 rpm. The drum turns very fast. It actually turns so fast that on the clockwise cycle when the motor brakes to reverse to the counterclockwise direction the drive gear will jump a tooth! If I hold the processor just right this will not happen :)

I need to slow down the motor. The JOBO drum directions talk of setting the rotation speed at 50 on multi-speed units. Any ideas how to slow this guy down?


So far I have done 10 sheets and all seem fine but the contrast is a bit lower than normal. I had been using a jobo print drum with 2 sheets in it. It also turned much slower. When I was modifying the tank to hold the big drum I managed to clean out a bunch of crap and installed new rollers. This got the motor to the correct default, very fast, speed.

In the print drum I would use rollo pyro at 7.5 min for nice negs. Prior to rollo pyro I used rodinal 1:50 for 12.5 min for nice negs. It would seem to me that the increased speed of the rotation would increase agitation and make a more contrasty neg; not less contrast as I am not getting. Am I on the right track?

thanks all

[Greg Blank]

:) Your drum is moving so fast the developer is not contacting the film. Like a pail of water when you swing your arm its staying in one spot. Seriously though the 75 means 75 RPM. Assuming you are doing 5 sheets you will need a total of 1,000 ml of chemistry. Instead of doing one developer run at say ten minutes do two at five minutes using 500ml each. That should give you plenty of coverage, and plenty of developer strength to processor all five sheets. You may have to play around with concentration until you get contrast to match what you are looking for. I would not mess with the motor to limit it.

[Jay DeFehr]

David,

It's possible the faster rotation is oxidizing your developer faster, leading to lower contrast negatives, and probably higher levels of general stain, too. Having left my ATL behind, but not my expert drums, I've been hand rolling, and the resistance is significant. I'm sure the expert drums are a lot harder on motors than any other type of drum. I rotate my drums very slowly, and I can feel the solution moving from one chamber to the next, and have a feel for how long it takes for the solution to fill and drain. I think a high rotation speed would create a lot of turbulence in the drum, and result in inefficient agitation. The idea is to get maximum solution movement with minimum oxidation, and turbulence works against both those goals. So I agree, you need to slow that motor way down.

There are a lot of members here who know a lot about electronics, and someone might be able to recommend a fix. Something like this might work:

http://www.ebay.com/itm/Vintage-Ohmite-Panel-Mount-Variac-2-Used-/180724204224?pt=LH_DefaultDomain_0&hash=item2a140082c0#ht_1190wt_1393

[Greg Blank]

Great idea break into the motor housing and screw with the DC motor make sure you Call me for the replacement motor it will be waiting. ;D

[atlcruiser]

I thought I would have an issue with the motor not turning the drum enough...never did i think it would turn too fast!

I was using 750 developer and 500ml of wash x 2 and 500 fixer. From what I read on the paperwork that should be plenty but I will try your idea of 2 runs with 500ml each run.

My LAST option will be to dig into the motor. I had hoped that one of the other JOBO processor controls with multi speeds might plug and play into this one.

I also have a couple of unirollers that will handle this just fine for B+W.

Thanks again Greg for a perfect transaction...the kidney scar will clear up soon :)

[Greg Blank]

The CPA and CPP2 processors ramp the voltage, guessing that is the case here. In other words as the weight load increases so does the voltage supplied to the motor. Eventually the relays that switch the motor polarity wear out becuase the RPM is trying to be maintained by the circuit design. Do not use the device Jay pointed out. The Motors are DC voltage supplied by the inbuilt AC transformer and then rectified to be DC to the motor. The variac is an AC supply device & you can not hook it directly to the motor. If you decide against my advice to leave the motor alone, at least make sure the processor is turned off and unplugged before opening and playing around with anything.

[atlcruiser]

Greg, trust me.....I am not digging into this motor anytime soon :)


Thanks for the explanation of how it works; even more reason not to mess with it

[John Koehrer]

So if you can't adjust the AC voltage, how about the DC?
If you're looking for a constant speed why not use a voltage divider?

[Jay DeFehr]

Thanks, Greg. Is there a similar device for DC motors? It seems I've seen one on a JOBO. The JOBO was plugged into the unit, and the unit was plugged into the wall- the motor itself was unmolested. I think I remember whose JOBO it was- I'll see if I can find out.

[Greg Blank]

There is realistically only so much info I can give, I am affliated if only now indirectly to Jobo and that bears an element of responsible answering,- consider that legal issues could be a factor:

Personally I don't give a damn if your socks burn off and the hair on your behind acts as a OC safe light :D

Could one wire a DC- power source to the motor? Maybe.
Would doing so produce problems - perhaps.
Would I provide documentational help- NO.

Could I fix these issues or modify said processor- most likely. But not in my best interest.

Thanks, for asking!