[stevebrot]

The K20D can handle the voltage through the pc sync port. Thanks for the info.

Ummmm...no. The PC port syncs electronically, the same as the hot shoe. The circuits are functionally isolated, but both are vulnerable.


Steve

[Not a Number]

The Sunpak 3600 and Vivitar 285 are not safe on modern cameras as they have high trigger voltages.

Some 285s have high voltage, it depends on when they were made. The only way to make sure is to measure the trigger voltage.

Question about vivitar 285 zoom thyristor flash - PentaxForums.com

[RebelCharlie]

Ummmm...no. The PC port syncs electronically, the same as the hot shoe. The circuits are functionally isolated, but both are vulnerable.


Steve

According to this pentax rep. the sync port can handle high voltages, not sure if it also applies to the hotshoe.

You Tube

You Tube

[stevebrot]

According to this pentax rep. the sync port can handle high voltages, not sure if it also applies to the hotshoe. Pentax K20D - YouTube

I remember that video, including the footnote regarding safely syncing studio strobes. The claim regarding higher voltages at the PC port caused some discussion here at PF. Your pondering regarding the hot shoe is pertinent. At the time Hoya would not confirm protection at the shoe and were noncomitant regarding voltage limits for either the hot shoe or PC fitting.

Flash trigger voltage - PENTAX official answer - PentaxForums.com

From the K20D manual, page 151...

You can connect an external flash to the
camera with a sync cord by using the X-sync
socket.

...followed by a warning...

* The use of high-voltage or high-current external flashes may cause a camera breakdown.

The same or similar text has been found in the manuals for all models having a PC port since. I don't remember if any K20D users here at the time sync'ed studio strobes or high voltage flash directly from the PC port. I don't know how often the topic has come up since, probably due to the ready availability of inexpensive radio sync since then.

I have not tried higher voltage on the PC port on my K-3, though if you give it a try with your K20D, I would be interested in the outcome. If you do go too high, the most likely outcome would be a camera freeze requiring a battery-out shut-down (personal experience at the hot shoe ) . Also possible is a fried circuit board.


Steve

[Not a Number]

I just found a copy of the Vivitar 283 service manual:

http://krebsmicro.com/283manual/vivitar_283.pdf

Regarding the Vivitar 285HV as I recall when used with the HVP-1 or 510V rechargeable battery it would bypass the main capacitor and trigger the tube directly. Ultra-fast recycle times as you didn't need to wait for the capacitor to charge.

When used on the 283 or standard 285 the normal circuit with the capacitor is still used but you benefit from faster recycle times as well as greatly increased number of flashes.

There are also battery packs by Quantum that can be used.

[Lord Lucan]

Regarding the Vivitar 285HV as I recall when used with the HVP-1 or 510V rechargeable battery it would bypass the main capacitor and trigger the tube directly. Ultra-fast recycle times as you didn't need to wait for the capacitor to charge.When used on the 283 or standard 285 the normal circuit with the capacitor is still used but you benefit from faster recycle times

So that is why the 285HV has the "HV" suffix (despite the fact that the trigger volyage is low compared with the plain "285" version). I may be wrong, but I'm surprised if the capacitor is bypassed when a high voltage external pack is used. Capacitors can be charged almost instantaneously if the supply to them is up to it. The two main bottlenecks in flash speed are the maximum current the batteries can produce without dragging their voltage down, and the power capacity of the inverter circuit.

An external battery pack can bypass those two bottlenecks, but there is no need to bypass the capacitor. I would think there would be quite a danger in letting an external battery get straight to the discharge tube. If the quench thyristor were to fail there could be quite a glass explosion as the whole battery started to run down through the flash tube unchecked.

[Not a Number]

I may be wrong, but I'm surprised if the capacitor is bypassed when a high voltage external pack is used.

I'm going off of memory from what I read about the HV 20-35 years ago. Ok, the HVP-1 cannot be used with the standard 285. It can be used with the 283. I went back to the user manuals so the information floating around on the Internet is incorrect. The standard 285 can use the LVP-2 pack which uses D-cell batteries.

According to the manuals you need to have fresh AA or the NiCad pack in the 285HV installed when using the HVP-1 in order to use the sync circuits. From what I remembered reading was the HV goes directly to the tube, it could have meant the flash capacitor. The flash tube uses 330+/-30V so the 510V is stepped down. Note the recycle time on the 285HV using the HVP-1 is 1.25 to 1.50 seconds with the internal NiCad pack and depending on if the rechargeable HV battery is used or not. On the 283 the recycle time is 1-3 seconds using the external HVP-1 batteries.

Using NiCad batteries shortens the recycle time from 9 to 4-5 seconds (full power flash).

283 no. flash & recycleSpecs (sorry too lazy to crop to the relevant text):




285:


285HV:


note: the 285HV has a "finite" number of flashes when using the SB-4 AC adapter because it needs AA batteries or the NiCad pack to power the sync circuits.

I haven't been able to find the user manual for the HVP-1 which would probably give more detailed specs than from the 283 system marketing brochure (blue page).