Durst 670

Luckypete · Feb 19, 2025

My Durst 670 has blown 2 bulbs in the space of a couple of months. I checked the voltage across she 2 terminals with my multimeter: one way measures 14.5 V the other way 11.4 V The transformer output says 11V & 12V. I presume the transformer is faulty?

koraks · Feb 19, 2025

Luckypete said:
I presume the transformer is faulty?

In a strict sense, not the transformer as such, but the voltage control circuit that goes with it. It's common on these. I've had one particular unit that measured OK, yet kept blowing bulbs. Since a spare was available, I never really got to the bottom of it.

These power supplies are getting kind of temperamental.

Luckypete · Feb 19, 2025

Looking at replacements there seems to be 2 different model/versions: one EST 305N Stabilised, the other not described as Stablised

Anyone could elaborate please?

koraks · Feb 19, 2025

The stabilized supplies have additional circuitry that keeps the bulb voltage constant even if the voltage on your wall outlet fluctuates. The non-stabilized units don't do this and the output voltage will fluctuate in correspondence with the input. Especially when doing B&W work, it's generally not really needed to use a stabilized unit (and arguably, it does fairly little for color work either). The stabilized units are more complex and more prone to failure. Many of course do still work, and if they break, they can usually be repaired by a skilled technician.

Luckypete · Feb 19, 2025

Im in the UK, anyone know of a company that could/would repair the transformer?

DREW WILEY · Feb 19, 2025

Where were the bulbs made? That can make a big difference.

Luckypete · Feb 19, 2025

This is what I used.

Luckypete · Feb 19, 2025

As advised...

Renato Tonelli · Feb 19, 2025

DREW WILEY said:
Where were the bulbs made? That can make a big difference.

That’s been my experience.
My bulbs labeled and sold by Durst seemed to last and last. The other ones not so much; I bought some that were really inexpensive and they blew within weeks. USHIO-branded lamps is what I have been buying of late and so far-so-good.

Luckypete · Feb 19, 2025

Can only seem to get Osram & Phillips here in the UK !!

DREW WILEY · Feb 19, 2025

That identifies the brands, but not the actual source of manufacture. Some brands offer both high quality bulbs and and very inferior ones made in China. Even with the same specification number, that can spell the difference between an enlarger bulb lasting ten years versus a few weeks.

I stick with Japanese made USHIO (or their Mexican made bulbs are also good), or try to find actual US made commercial grade GE bulbs (GE no longer makes bulbs at all, but plenty are still around). EU made Eiko is also good. Going with private label "official" enlarger bulbs just means you're going to pay five or ten times as much for the same thing. Durst themselves never made bulbs, just bought them from another source. But almost any cheapo equivalent made in China, including most Phillips items, is going to be disappointing.

ic-racer · Feb 19, 2025

Bad socket can cause that [blowing bulbs], presuming you have a triac based PWM driving circuit, rather than a simple transformer.

DREW WILEY · Feb 19, 2025

Yes, sockets should be periodically checked for corrosion.

Luckypete · Feb 20, 2025

I have a TRA 305N which I believe is the "non-stabilised" unit – I have ordered a EST 305N.

I will keep searching for alternative bulbs, however at the moment I have no choice other than Osram or Phillips, it does not specify where they are manufactured.

I would also prefer to replace the bulb socket, it looks ok, but its seems like a sealed unit and I cannot find a suitable (new) replacement.

I will try to find an electronics outfit who can repair my TRA 305N and upgrade the voltage output circuit, it cant be that difficult.

koraks · Feb 20, 2025

Luckypete said:
I have a TRA 305N which I believe is the "non-stabilised" unit

Then there's really no reason to suspect the power supply is the culprit.

Luckypete said:
I will try to find an electronics outfit who can repair my TRA 305N and upgrade the voltage output circuit, it cant be that difficult.

The unregulated TRA305N doesn't have a 'voltage output circuit'; there's nothing to repair.

Luckypete · Feb 20, 2025

I am no electronics guru here, however I measured the voltage at the bulb socket and it is 14.5V +-

If it's just a simple step-down transformer then could it be faulty?

Oh by the way the insulation around the two bulb pins was really badly corroded or degraded and discolored.

koraks · Feb 20, 2025

Luckypete said:
If it's just a simple step-down transformer then could it be faulty?

Nope. Transformers don't fail by giving too high a voltage. They rarely fail to begin with, and if they do, they invariably fail open - so no more power coming out.
You should measure the voltage with a bulb installed as it'll drop some under load.

Luckypete said:
Oh by the way the insulation around the two bulb pins was really badly corroded or degraded and discolored.

OK, but it's more about the contacts within the socket.

Luckypete · Feb 20, 2025

Yes I agree: and thanks for your knowledge about the transformer. As I said I would like to change the socket but cannot find the same or similar – as of now !

I will measure the V under load as you suggest.

At least I will have a spare transformer

BobUK · Feb 20, 2025

Luckypete said:
I have a TRA 305N which I believe is the "non-stabilised" unit – I have ordered a EST 305N.

I will keep searching for alternative bulbs, however at the moment I have no choice other than Osram or Phillips, it does not specify where they are manufactured.

I would also prefer to replace the bulb socket, it looks ok, but its seems like a sealed unit and I cannot find a suitable (new) replacement.

I will try to find an electronics outfit who can repair my TRA 305N and upgrade the voltage output circuit, it cant be that difficult.

I have had my Durst enlarger since the 1980s. Had to replace the bulb two pin socket twice. The last time the light was flickering due to the corroded connector.
I gave up on replacing the socket, and have replaced it with two small lengths of tinned brass tube soldered to the wires and pins of the light bulb.
Only problem is if the bulb goes I will have to dig out the soldering iron to replace it. Not a great problem though.

BobUK · Feb 20, 2025

Just had a look at ebay UK. DFB Sound and Light have socket G6.35 item code 355834337078 priced at £2.99 free postage.
At those prices you could buy a couple of spares for the future.
Disconnect the power supply.
Cut the old socket off, and solder the new one in place, plus some heat shrink insulating tube over the joints.

Before buying check for yourself that that is the correct socket for your lamp.

If you are anything like me you will put the spares away in a safe place, and promptly forget where.

Luckypete · Feb 20, 2025

Yes I had a look at that – however it states 75 Watt Max.

I rather like your own solution with the tube/soldering.

Did you remove all the connections shown here and have the wires soldered to the tube at one end and the bulb at the other – it eliminates the many connections for sure.

Reply to Koraks:

"The unregulated TRA305N doesn't have a 'voltage output circuit'; there's nothing to repair."

See attached pic. this is a circuit ??

koraks · Feb 20, 2025

Luckypete said:
Yes I had a look at that – however it states 75 Watt Max.

Does it?

G6.35 GX5.3 Bi Pin Ceramic Halogen Lamp Holder for Low Voltage Bulbs | eBay

Lamp Base: G4, GU4, GX4, GZ4, G5.3, GU5.3, GX5.3, G6.35, GX6.35, GY6.35, GZ6.35. The Ceramic dichroic lamp holder for high temperature applications that include mainly Tungsten Halogens, Incandescent and HID bulb types.

www.ebay.co.uk

I don't see it. Anyway, that socket should work fine.

Luckypete said:
See attached pic. this is a circuit ??

Yes, you're correct. So that's a stabilized supply. Sorry for not having checked your earlier assumption that it was a non-stabilized unit; I assumed you had verified it.

BobUK · Feb 20, 2025

Whilst I had the opportunity I replaced the wires from the small screw terminal block to the socket with slightly longer wires.
The brass tubes were cut halfway across then along one half of the length. A fine jewellers saw was used for the cut.
The slotted end of the tubes were flattened slightly to be a good fit around the lamp pins.
I tinned the lamp connecting pins with solder before making the connections.
Then soldered everything up.
Use some insulating heat shrink tube over the solder joints for safety.

Small brass tubing can be purchased in about 10 inch lengths from model making shops. The sort of place that sell bits and pieces for radio controlled planes, helicopters, cars etc.

Steve906 · Feb 20, 2025

Its not really a good idea to solder to these bulbs. The lamp holders are supplied with crimped in leads with high temperature insulation.
The lamp can easily get hot enough to melt solder and damage normal insulation !

The following is for my Modular 70 -

The voltage to the lamp is AC (chopped not PWM if the stabiliser is used) and should be measured on an AC meter with floating ground.

I use the Osram xenophot 64627 HLX EFP 12v 100w gz6.35 they say made in Germany on the lamp and box. They also have a warning that the lamp can reach >500 deg C

The holders are listed on amazon UK - search "g6.35 socket" also MR16

It may not be relevant but my transformer outputs 17V AC and 12V AC - the 17v is regulated by the stabiliser to 11.7v chopped AC
The 12V is only used by micro head and/or other accessories unless the stabilser is removed (it was an option on the M70).

Steve.

BobUK · Feb 20, 2025

Steve906 said:
Its not really a good idea to solder to these bulbs. The lamp holders are supplied with crimped in leads with high temperature insulation.
The lamp can easily get hot enough to melt solder and damage normal insulation !

I use the Osram xenophot 64627 HLX EFP 12v 100w gz6.35 they say made in Germany on the lamp and box. They also have a warning that the lamp can reach >500 deg C

Steve.

I have shortened the quote.

Hello Steve.
Perhaps I have been lucky so far regards melting solder.

I would have thought the temperature of the lamp would be measured in front of the reflected element. Not around the back by the connectors. The front of the lamp would be hotter I think.

I ditched the correct connector due to arcing inside the tubes that the bulb pins go into.

Up to now things have gone well.

Possibly 500c could be reached if the bulbs are used in a slide projector for a long time continuous.

It would be nice to hear other peoples thoughts on this.

ps I will borrow one of those laser thermometers tomorrow, and see what it reads.

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