Replacement lamp socket for Focomat v35

logan2z · Jul 3, 2019

Does anyone know of a good source for a replacement v35 bulb socket? The lamp base is of type GZ6.35. Pictures of the existing socket attached (apologies for the poor quality, my cell phone camera seems to be slowly dying). I searched around online but didn't see anything that looked exactly the same. One side of the socket is stamped '881' if that's useful information.

logan2z · Jul 3, 2019

Thanks to a kind Photrio member it looks like I may have found a suitable replacement socket. Thanks!

mgb74 · Jul 6, 2019

Once confirmed, why don't you post the details here. Will help someone else looking in the future.

AgX · Jul 7, 2019

Here a european source of various models:
http://www.wittnercinetec.com/epage...c-Super8-16mm-Film/Categories/Lampenfassungen

logan2z · Jul 7, 2019

I bought mine from a place called Bulbworks. The '881' on the original socket refers to a part number from Bender+Wirth, apparently the original supplier to Leitz.

https://www.bulbworks.com/light-bulbs/881

I haven't received the socket yet so don't know how well it works, but will post a follow-up once I do.

AgX · Jul 7, 2019

Bender&Wirth... I forgot about them. Manufacturer of such sockets and back then even present on Photokina.
Today they have less choices than Wittner I linked to above.

logan2z · Jul 13, 2019

I received the replacement lamp socket and it seems to work well. I had a noticeable flicker from the bulb in the Focomat when using the old socket that looks to be fixed with the new socket - or is it? As a simple test, I decided to use the light meter from my RH Designs Analyzer Pro to repeatedly measure the light output of the enlarger in the same spot on the baseboard with no negative in the carrier. Most of the measurements were the same but occasionally I would get one that read higher or lower. Oddly, I never did perceive an obvious change in light level as I did before replacing the socket. To eliminate the meter as a source of erroneous readings, I repeated the experiment with my Beseler 23C. Every reading on the Beseler was identical. So, I have to assume that the light output of the v35 is still fluctuating somewhat despite me not being able to actually perceive the variation.

I'm not much of an electronics person. Can anyone suggest how I might be able to track down the source of the problem in the v35?

OGTrout · Jul 15, 2019

Could it be the transformer for the lamp? I have a Durst colour enlarger, the socket on mine is the same and I also replaced it with the same part (BenderWirth 881), but while the light was more consistent than before it still isn't as consistent as I feel it should be. I also had trouble with my prints coming out darker than my test prints if I did the print as a cumulative exposure at once, e.g using 15 seconds instead of the 3 x 5 seconds on a test strip. I didn't track down the problem, but the transformer had crossed my mind.
I'm now using a condenser head as I prefer the way it looks but also find it much easier to work with.

logan2z · Jul 15, 2019

OGTrout said:
Could it be the transformer for the lamp? I

It could be, I'm just not sure how to test that or replace the transformer if it's the culprit.

MattKing · Jul 15, 2019

OGTrout said:
I also had trouble with my prints coming out darker than my test prints if I did the print as a cumulative exposure at once, e.g using 15 seconds instead of the 3 x 5 seconds on a test strip.

That is normal - 15 seconds straight includes just one set of ramp-up and ramp-down exposures, while three 5 second exposures includes three sets of ramp-up and ramp-down exposures.

OGTrout · Jul 18, 2019

MattKing said:
That is normal - 15 seconds straight includes just one set of ramp-up and ramp-down exposures, while three 5 second exposures includes three sets of ramp-up and ramp-down exposures.

That's about what I thought, however it had never been an issue with the condenser heads (230v lamp, no transformer) I'd used previously and I've never used any other diffusion enlarger to compare against. In general I seem to find the b+w head easier to achieve the prints I want, and find it easier moving between negatives with less testing and less wasted paper.

glbeas · Jul 18, 2019

logan2z said:
It could be, I'm just not sure how to test that or replace the transformer if it's the culprit.

If you have a voltmeter try to measure the voltage at the leads with the bulb in place and operating. Any variation should show itself then.
It could also be the meter if the light level is different between the enlargers. Try the comparison again with the lenses stopped down to match the light levels of each other. Be sure there is no other source of light that could affect the results.

logan2z · Jul 18, 2019

glbeas said:
If you have a voltmeter try to measure the voltage at the leads with the bulb in place and operating. Any variation should show itself then.
It could also be the meter if the light level is different between the enlargers. Try the comparison again with the lenses stopped down to match the light levels of each other. Be sure there is no other source of light that could affect the results.

Thanks for the suggestion, I'll try and measure the voltage at the bulb to see if there is any variation over time.

Re: the meter, I wasn't looking for the same reading across the two enlargers, just that it was consistent for a given enlarger over time. It was consistent with the Beseler but varied with the v35. I did this under darkroom conditions so I don't think there were any other sources of light that could have affected the measurements.

glbeas · Jul 18, 2019

Have you also checked the electrical connections elsewhere in the unit? Switches, plugs, etc. If there is a failing connection the resulting arcing can cause the variations, which is what your old socket was doing.

logan2z · Jul 19, 2019

glbeas said:
Have you also checked the electrical connections elsewhere in the unit? Switches, plugs, etc. If there is a failing connection the resulting arcing can cause the variations, which is what your old socket was doing.

I haven't done that yet. I'll have to remove the baseboard and look at all of the connections to see if there are any obvious issues.

Replacement lamp socket for Focomat v35

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