Need help identifying old diode in WSW preamp

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rjb5191

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Oct 26, 2017
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162
Location
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I suspect I have a bad diode in my old WSW 811 432 Line amp / preamp. When i move it physically in the slightest, it seems to go open. I would like to replace it but have no idea what it is. I can't find schematics and I can't find anything in a google search that looks similar. Its from a 1960 vintage console so I'm guessing it's germanium.

In the picture its the small brown component with fine leads and a black and green dots, down and left of center in the photo. Any help is much appreciated!
 

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I don't know what Diode that is, but some ideas to help out:

- if it works but intermittently, you can carefully unsolder it and measure it with a component tester, even if some times it goes open you can try to measure it different times until you get a reading, then at least you will have some information about it's characteristics that will be useful to choose a replacement

- another idea is if you have another channel, take the Diode from the good channel and measure it

You can measure it with a cheap unit like this one, very useful tool:
https://www.aliexpress.com/item/32310123631.html
Or a Peak Atlas, much more expensive:
https://www.peakelec.co.uk/acatalog/dca55-atlas-dca-semiconductor-analyser.html
 
I don't know what Diode that is, but some ideas to help out:

- if it works but intermittently, you can carefully unsolder it and measure it with a component tester, even if some times it goes open you can try to measure it different times until you get a reading, then at least you will have some information about it's characteristics that will be useful to choose a replacement

- another idea is if you have another channel, take the Diode from the good channel and measure it

You can measure it with a cheap unit like this one, very useful tool:
https://www.aliexpress.com/item/32310123631.html
Or a Peak Atlas, much more expensive:
https://www.peakelec.co.uk/acatalog/dca55-atlas-dca-semiconductor-analyser.html
The Peak is nice - it will tell you which end is which, if it is germanium or silicon, and roughly if its good - but you don't need a Peak for that. Germanium transistors and diodes will show a lower resistance (and voltage drop). We have a Peak here, it get used very seldom in real work. It mostly gets used when we get large shipments of unsorted active devices in. or when someone mixes up a large bunch of LED's while prototyping. There it is great for rapidly rough sorting things.

have you just tried hitting it with flux and reheating the connections carefully with your soldering iron? (use a heatsink if you don't do lots of delicate soldering, germanium stuff hates heat)
 
some diodes get pretty warm - Im going to wander out and see if any of our modules are open - kind of running out of steam here tonight, and coffee. I think I could find the same module and quick test ours. We may have replacements in stock even.
 
I am looking at an 811430B - there are a few more out there in this size format/generation. I will look in the morning I need got to climb a ladder and pull a large box of modules down to check them out. It's late. There is much here from that era - I may have an exact replacement if needed. I just need to do some digging in the daylight.
 
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gotta love the input impedances on these... I am thinking our Ribbons are going to be fun with these things.
 

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im not sure where your diode is located - is it part of a temperature compensation scheme?
Sadly I don't have the schematic; information on these is scarce. You can see that there is a second diode that is essentially mirrored with symmetric circuit values around it. Temperature compensation seems reasonable given the germanium transistors. This unit has been having a bit higher hiss than my other and I've been trying to track the reason for that down. I really like these units.

P.S. with your bounty of WSW gear, don't be shy to send some my way if your warehouse is bursting at the seams! ;)
 

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..this is not a line amp /preamp - it's a summing amplifier..

In another mix-amplifier from the 811-series (attached 811-514), diodes are all PSU zeners, protection, and relay decoupling. All non-critical..

Are you sure you're not looking at a NTC? Those are weird and mission-critical

/Jakob E.
 

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probably time to put a meter on the mystery component. you could fire up the channel, and measure the voltage drop across the device. Then do you math for resistance running, let it cool down, lift one leg of the thing and measure resistance. compare that to your running number...
 
..this is not a line amp /preamp - it's a summing amplifier..

In another mix-amplifier from the 811-series (attached 811-514), diodes are all PSU zeners, protection, and relay decoupling. All non-critical..

Are you sure you're not looking at a NTC? Those are weird and mission-critical

/Jakob E.
Hey Jakob, Do you happen to have the Schematic for 811-516? There are a couple of those laying around here too.
 
..this is not a line amp /preamp - it's a summing amplifier..

In another mix-amplifier from the 811-series (attached 811-514), diodes are all PSU zeners, protection, and relay decoupling. All non-critical..

Are you sure you're not looking at a NTC? Those are weird and mission-critical

/Jakob E.
I know this is about the repair first, and not really about how to use this amp, but isn't the 811514 that you postet pretty much identical to the preamp section of the 811510 - so the 811432 should be pretty similar to the 811430 without the switches, or am I completely wrong about that. Sure, by designation they are summing amps, but the WSW stuff from that era is pretty much all "universal" amps albeit with slightly different configurations, right?
 
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