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1970 Junghans Starburst w726 transistor

OZtralia

By OZtralia
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OZtralia New Member

OZtralia

Posted
Posted

Hello from Oztralia .. my name is AL and I am new to this forum ... I am on a mission to see if I can fix my 90 year old Mothers Junghans Starburst Wall Clock.

I may be asking a question that has been covered many times and I apologize if that is the case, these old clocks and their simple movements just give up when they are ready.

I sent the movement to my tech guy (not clock doctor) in Melbourne who has in fact repaired many of my circuit boards etc. and he did not claim to be able to fix it as it was not his typical line of work. He did however get the movement to work for all of 5 minutes using an AC122 resistor and did confirm everything else is working with the exception of that resistor which he pronounced as DOA/Faulty on an overseas purchase. I know I can put a quartz movement from Japan in as a replacement IF such a thing existed today in Australia with all the knockoff poor quality parts that are available to us but that is not what sits well with this Classic Clock if you know what I mean. Reading a few posts from you website, when the correct questions are asked, I am led to believe my Tech guy would need a Germanium Transistor but have no idea for sure as I can only Google possibilities.

Summary:- Am I to concede defeat as it has been 7 months so far ... OR ... is there a magical place I can purchase this resistor/s

Cheers AL 

OZtralia New Member

OZtralia

Posted
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Posted
On 9/7/2024 at 6:08 PM, praezis said:

If you search the net for transistor AC122 you will find many.

Frank

Hi Frank and Thanks for the suggestion,

Sorry I may have worded things incorrectly. The ac122 is no good as it only ran for 5min, I am looking for the same germanium transistor that was used on the w726 movement back in the '70s or a modern equivalent as i believe it is the missing link for a working clock again. Do you or anybody else on the forum have some idea as to where I might find such a transistor? ... I see you are in Germany and that is where Junghans originated from so I have my fingers crossed.🫰👍

Cheers AL

On 9/7/2024 at 6:18 PM, RichardHarris123 said:

Hello and welcome from Leeds, England. 

Cheers Richard ... Thanks

On 9/7/2024 at 8:10 PM, Nucejoe said:

Welcome to the WRT forum.

Cheers Nucejoe ... Thanks

rjenkinsgb WRT Addict

rjenkinsgb

Posted
Posted
24 minutes ago, OZtralia said:

The ac122 is no good as it only ran for 5min, I am looking for the same germanium transistor that was used on the w726 movement back in the '70s or a modern equivalent as i believe it is the missing link for a working clock again.

Germanium transistors have not been manufactured in a very long time.

There are many "new old stock" ones around, but many have degraded to the point they are useless.

The only way  to get a decent one is to buy a batch and go through them with a transistor tester, to see which actually work, then use the best one.

I have a batch of a dozen (I think) AC128 for a repair a couple of year ago; only three actually worked as they should, the others varied between very leaky and totally useless.

AndyGSi Distinguished Member

AndyGSi

Posted
Posted (edited)
33 minutes ago, rjenkinsgb said:

The only way  to get a decent one is to buy a batch and go through them with a transistor tester, to see which actually work, then use the best one.

If you buy from a reputable supplier and not eBay then they'll have already done this.

Edit

Unless it's a reputable supplier that also has an eBay listing.

https://www.ebay.co.uk/itm/254202098283

Edited by AndyGSi
  • Like 2
praezis Distinguished Member

praezis

Posted
Posted

At first I would not hesitate to try a silicium PNP transistor. Sometimes they work, too, though their B-E treshold is higher (GE 0.3 V, SI 0.6 V)

Frank

rjenkinsgb WRT Addict

rjenkinsgb

Posted
Posted
5 hours ago, praezis said:

At first I would not hesitate to try a silicium PNP transistor

Silicon transistors require a higher base bias; I found the original patents for the clock circuits, and those do not have any real bias to bring the base in to operating range, relying on the very low base voltage threshold and possibly even the leakage of the germanium devices.

It would not do any harm to try a PNP silicon device, though it looks unlikely that it would work if the circuits I found were accurate.

 

6 hours ago, AndyGSi said:

Unless it's a reputable supplier that also has an eBay listing.

Those are actually gain-graded devices - the higher gain ones they have should be perfect for the clock!

  • Like 1
AndyGSi Distinguished Member

AndyGSi

Posted
Posted
17 minutes ago, rjenkinsgb said:

It would not do any harm to try a PNP silicon device, though it looks unlikely that it would work if the circuits I found were accurate.

I think if it's just running off a single 1.5V cell then you're right that there
wouldn't be sufficient voltage to operate with a silicon transistor.

nevenbekriev Distinguished Member

nevenbekriev

Posted
Posted

Yes, it operates on single 1,5V battery, but the base is not driven by the battery, it is driven by the base coil, which generates voltage from the passing magnets through it. So, it is possible to use silicium transistor, but slight modification of the cirquit is needed as to add some bias to the base of transistor.

My first question will be if the coils are intact, as this is the main problem in such watches. You don't need more powerful transistor and there is no reason AC122 to last for only 5 mins. The resistance of the coils there should be several kiloohms and no big current can pass thru the transistor.

  • Like 1
AndyGSi Distinguished Member

AndyGSi

Posted
Posted
2 hours ago, nevenbekriev said:

Yes, it operates on single 1,5V battery, but the base is not driven by the battery, it is driven by the base coil, which generates voltage from the passing magnets through it. So, it is possible to use silicium transistor, but slight modification of the cirquit is needed as to add some bias to the base of transistor.

My first question will be if the coils are intact, as this is the main problem in such watches. You don't need more powerful transistor and there is no reason AC122 to last for only 5 mins. The resistance of the coils there should be several kiloohms and no big current can pass thru the transistor.

This isn't a watch it's a wall clock.

  • 2 weeks later...
OZtralia New Member

OZtralia

Posted
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Posted

Thank You all for your support on this problem of mine it is very much appreciated. To clarify a little more I have attached some images as I have absolutely no idea what is what when you go and get all technical on me but I am absorbing your one on one discussions with great interest. Andy's link to a UK ebay site shows germanium transistors NOS are available but what would the specs of my original one be so that I can buy one that might look different but do the job?       

image001.jpg

image002.jpg

IMG_20240921_091841.jpg

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