Vivitar 283 sync voltage reduction, power level control

[Charles Krebs]

I use the old Vivitar 283 electronic flash for my microscope flash. (See here for some info, and the actual modification for the microscope can be seen at the bottom of this page).

I have a bunch of these units that I keep as "spares" since they have been discontinued for some time. Most of mine are made in Japan and have a sync voltage of around 275 volts, which does not co-exist well with many digital cameras and radio slaves . I wanted to give one to my son for his "strobist" endeavors, but they needed to be modified. (Toward the end of their production, these flash units were made in Korea and China. Most of these do not have the high trigger voltage of the ones made in Japan. It's easy to measure the voltage via the two contacts on the flash hot foot)

In the past I've used a Wein Safe-sync to lower the trigger voltage, but they cost more than the used flash unit itself. There were a couple of DIY circuits that I had seen in the past and relocated a good one here:
http://repairfaq.cis.upenn.edu/Misc/zpaofu1.pdf

I'm no electronics wizard, but it's very simple to assemble and the parts cost me less than $2.00. It works beautifully, and lowers the sync voltage to about 4.6 volts. (For one of the cameras used with my microscope flash I use this circuit wired into a flash sync cord instead of the Wein Safe-Sync). But I thought it would be fun to fix a couple of these units “internally” along with a nice variable power control. I looked at the Vivitar 283 repair manual and realized that, rather than disassembling the flash unit, it would be possible to utilize some of the contacts on the front to incorporate this circuit. (The other two front contacts are used to vary the power outputs). So this circuit (for trigger voltage reduction), along with a small rotary switch set up with resistors (for varying the power output) were put into a small box attached to the front of the flash.

This first image shows the front of a Vivitar 283 with the sensor unplugged. The two contacts marked with the red arrows are the ones that are used to vary the power output with different resistor values (found here).

The contacts marked A, B, and G are used with the voltage reduction circuit as indicated.





This is the voltage reduction circuit as I put it together for the small box. It could be made much smaller if needed.


Here's a small 12 position rotary switch that has been set up with resistors to provided 1/2 stop power level increments (Full power to -5 1/2 stops).


Here's the finished flash. I've added an inexpensive "eBay" metal foot to the flash. This also provides a standard "PC" connection.


An important note... modifying the sync voltage in this manner lowers the voltage to the flash shoe contacts. The (proprietary) Vivitar flash connection on the side of the flash remains unchanged. I've placed black tape over it, and if I need a corded connection I use the "new" PC connection in the metal foot. (But generally these are fired with either an optical slave or a radio slave via the hot foot).

These have worked out very nicely. If all you want are a couple of fairly powerful, shoe mount, manual flash units with an adjustable power range, it sure is far more economical than SB-900's or 580 EX's.

[Planapo]

Much appreciated, Charlie!

I still have to put my Vivitar 283 units to some good use. Despite your and Rik's great help my DIY project of last summer ground to halt when I found out that the soldering gun we have was much too powerful for such a job, and then as I have hardly any experience with practical electronics and soldering, my milquetoast me got a bit hesitant, and so the project is still unfinished... (Hope I'm using that "milquetoast" correctly here? )

But meanwhile I have found me a suitable soldering iron of low power and want to proceed with this project, especially with the new information you give here. One question remains: On your website you've kindly provided the detailed resistance values corresponding to power reduction given in - f-stops. Thing is, with the standard resistors I can purchase from my supplier, I mostly can't get combinations that match exactly the values you provide. Would I be fine with the nearest possible resistance values that are achievable with combinations of the standard resistors I can buy?

Thanks again for sharing all this!
--Betty

[Charles Krebs]

Betty,

Don't worry about matching exactly. For each value I use either a single resistor or, at most, two to get close to the values provided. Somewhere I have a list of the resistors I used (all common values). I'll look for it later tonight.

[rjlittlefield]

(Hope I'm using that "milquetoast" correctly here? )

Looks correct to me. And thank you for prompting me to look up the etymology of that word:

[Wiktionary] From the character Caspar Milquetoast of the comic strip The Timid Soul, created by Harold Webster and first published in 1924.

--Rik

[elf]

Is the metal foot necessary or is it more for the convience of the PC connection?

[Charles Krebs]

Elf,

Metal foot is not necessary. (If you have an unmodified 275 volt version I strongly recommend that you do not install this type of metal foot, or you will regularly be surprised by small shocks if you handle the unit and touch the base contact and the metal foot simultaneously ). I like the way it locks down, and like having the standard PC connection even if I rarely use it.

Betty,

Here are the "average" of the 4 units tested some time ago, and, in parenthesis, the resistors I used on the 12 position switch:

Full 250,000 or greater (can leave position open without resistor)
-.5--150000 (150K)
-1----78400 (75K+3.3K)
-1.5--57000 (56K +1K)
-2----35290 (36K)
-2.5--26500 (27K)
-3----17720 (18K)
-3.5--12350 (12K+330)
-4-----9550 (10K) or (6.2K+3.3K)
-4.5---7600 (7.5K+100)
-5-----5680 (5.6K+100)
-5.5---4400 (4.3K+100)

That's twelve positions. If you toggle to a second switch, like I did for my microscope "box" you can use these values to reduce power still more.

-6-----3150 (3K+100)
-6.5---2400 (2.4K)
-7-----1530 (1.5K)
-7.5----800 (820)
-8------155 (150)

[Planapo]

Thanks much for the values of the norm-resistors, Charlie, already added to my shopping list!

Then I had a look at my Vivitar units again, all "random bay-samples":

Made in Japan, ser.-no. 2752459, 109 V
Made in Japan, ser.-no. 2056330, 104 V
Made in Japan, ser.-no. 2038000, 107 V
Made in Japan, ser.-no. 1064313, 94 V

and am surprised now that, though they are all made in Japan, the voltage values I had measured were all well below 250 V
since you wrote:

Most of mine are made in Japan and have a sync voltage of around 275 volts...Toward the end of their production, these flash units were made in Korea and China. Most of these do not have the high trigger voltage of the ones made in Japan.

I am a little in doubt about my volt meter, or should I rather doubt my measuring skills. To be on the safe side, I think I will better add this voltage reduction circuit to the control unit, aah, milquetoast again!

Leading over to
Thanks Rik for the linguistic help! Well, um, you know being a learner of English as a foreign language, it's my ultimate goal to blend in with the native speakers. But that I have made you look up the etymology of "milquetoast" now gives me the slight impression that sometimes I must stand out quite a lot using odd or funny vocabulary without even realizing it.

--Betty

[rjlittlefield]

But that I have made you look up the etymology of "milquetoast" now gives me the slight impression that sometimes I must stand out quite a lot using odd or funny vocabulary without even realizing it.

I have heard the word frequently enough, but only spoken, and in my head I had always imagined it as "milktoast". Seeing it written as "milquetoast" prompted me to investigate, whereupon I learned that my imagined spelling was simply wrong, not a regionalism as I had hoped. Fear not, aside from asking "is this right?" -- which of course no native speaker would ever do -- you could easily blend in with us native speakers simply by dumbing down your vocabulary and making an occasional mistake!

I am a little in doubt about my volt meter, or should I rather doubt my measuring skills.

I am not familiar with the triggering circuits in those flash units. There do exist simple circuits that would put 275 V across one voltmeter while only putting 100 V across another. Such circuits are characterized by having a high internal resistance that greatly limits their ability to supply current. They can be measured accurately only by using a meter with high input impedance. Most digital meters these days have input impedance of 10 M ohms, but I have seen some with only 1 M. Perhaps this is the source of the difference. Or perhaps your flashes really do have a different open-circuit trigger voltage.

--Rik

[lothman]

Thanks Charles,
as always a very helpfull instruction. May I use this thread for another question.

What has to be done if I want to use another flash tube as the original built in. This would allow to achieve a lot smaller setup or even a ring flash tube for a darkfield illumination with a microscope lens and perhaps still having ttl control of the camera .

Any ideas what specification the built in flash tubes have and what to do if they are replaced with one /severla smaller ones.
Regards
Lothman

[elf]

I've recently acquired several Vivitar 283s and am planning to do the flash power modifications but not the sync power modification as I will be using wireless triggers. What was the reason to use a set of resistors instead of a potentiometer for setting the flash power?

[Charles Krebs]

elf,

The values needed do not match up "nicely" with the travel on any potentiometer I've tried, regardless of the "taper" (and I have tried many different types). As a result you may have a great amount of rotation for some 1/2 stop changes, and then so little rotation for the lower powers that it becomes hard and annoying to try and set a specific value. I've settled on using discrete resistors in half stop intervals with switches that have nice click stops. I can change power levels by "feel" without even looking at the dials. Just makes things simpler and faster.

[elf]

Thanks. I plotted the resistor values and it's easy to see why it would be hard to get the lower values.

I've also been thinking about building one of these to control multiple flashes: http://code.google.com/p/strobist-proje ... e-trigger/. It allows you to set the quench time so it may be possible to get even lower power output from the 283s and also allow using other flash units.

[AndrewC]

Thanks. I plotted the resistor values and it's easy to see why it would be hard to get the lower values.

I've also been thinking about building one of these to control multiple flashes: http://code.google.com/p/strobist-proje ... e-trigger/. It allows you to set the quench time so it may be possible to get even lower power output from the 283s and also allow using other flash units.

The link you gave works by using the fire and quench signal lines you get on TTL flashes. The Vivitar 283 mod's work in a different way by adjusting the R component of an RC timing circuit. Not completely transferrable.

If you have any familiarity with electronics and microcontrollers it is very easy to make something allow precise control of TTL flashes - my favourites are Nikon SB-23 strobes.

[elf]

Thanks Andrew. You saved me a lot of soldering time I have an inexpensive transmitter and reciever coming from Hong Kong to experiment with. If the 283s and the wireless trigger don't work well, I'll build one for TTL flashes.

[Charles Krebs]

I have an inexpensive transmitter and reciever coming from Hong Kong to experiment with

elf... don't know which one you're getting. I've been using the RF602 units since the end of last year and they've been very good. Thing is... some of these will not like the high voltage of the older Vivitar 283's. So it might be worth checking and/or just lowering the sync voltage if you have one of the "high voltage" Vivitars.