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Old 9th Apr 2021, 5:00 pm   #1
Jez1234
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Default Bruel and Kjaer 2610 Measuring Amplifier

Both a success story and salutary warning that even an old hand at this game can fall foul of his own assumptions...

I've had this for quite some time. A cal sticker on it said it was due cal in 2000 and it can't have been more than a year or two after this that it (and in fact a whole lot of other top quality test gear), came my way from an ex colleague at what had been an old GEC-Plessey place which had changed hands and was trading under a new name.

I'd got many items working already when I came round to looking at this item.
The immediately obvious problem was that on powering up the needle pegged against the anticlockwise backstop.... I can almost hear the howls of laughter at this point from those familiar with this instrument!

Whilst I received B&K handbooks and even service manuals for some of the B&K gear I acquired there was no documentation on this (If anyone can help remedy that it would be most appreciated!) and it took me a few years of trying on various web forums etc until eventually, after describing the issue, someone emailed me the parts of the service manual pertaining to the metering and its calibration etc.

Well, after maybe 10 hours work split over 3 or so attempts over the years I was no nearer to finding the fault... in fact I could find no fault as such but for some bizarre reason the needle continued to peg to the left...

Now some of the tests I'd made which included measuring the outputs at the DC and AC outputs of the instruments had basically told me it was A1... but all my experience was telling me that no instrument in working order pegs its needle like that.... All the evidence was actually staring me in the face once "the penny dropped"!!

But.... to get back to a few days earlier, when I powered it up again this week, determined to get to the bottom of this, non of the LED's lit up... I quickly found that the smoothing cap for the 6V regulated supply had gone S/C! I did a few more tests and found a couple of 220uF 16V blue Philips that were measuring about 20R ESR and one of these was the input cap to the measuring section... Hmmm.. So these were also replaced.

Well this had the 6V supply returned and the LED's lighting but several other functions, oh including the 3 LED's on the right of the instrument for averaging time, had not been returned to normal service... The meter now didn't respond at all (I should have said that although pegged to the left enough input signal would move it up the scale) and the DC output was at a fixed seemingly random voltage.

I can only guess at leakage current having needed time to drop in the new input cap but after leaving the thing switched on and rather dejectedly going for a cuppa and ciggy I noticed about 30 mins later that the 3 extinguished LED's had magically lit up! Still nothing on the meter though even though I'd left it with the cal signal switched on. I left it still on whilst doing a bit of housework and maybe an hour later I noticed that the meter was now showing precisely the correct reading for cal signal!

I was now in fact simply back where I'd been in the first place before the S/C smoothing cap and temporary strange behaviour of various functions.

I read in more detail the cal instructions I had and made some more measurements until I came up to the bit about "inject blah blah mV and check for FSD (it passed this), now reduce signal by precisely 30dB and check that meter reads 0dB"... well this is where the mixture of joy and swearing happened !! 0dB and 1 on the 1 to 10 scale of the meter are at the point where the meter needle resides with no power on!! Argh!! Those ****** Danes!! And ****** stupid me who must have looked at that meter 100's of times and not spotted this!

It's only meant to peg the needle to the left without input signal isn't it! Doh! i.e on the 30V range the AC and DC outputs give zero output for zero input whilst the needle sits pegged to the left, off scale, and as the input reaches around 0.7V the meter starts to move until at precisely 1V input the needle is where it would be with the instrument switched off... and indicates precisely 1V!!

I'd been so blinded by my assumption that any instrument that pegs the needle like that is faulty that I'd spent hours and hours looking for the cause of this mysterious voltage offset "fault", in conjunction with the partial schematics I have yes but without bothering to read in detail the text parts... well there was no point in the fine details till I'd got this DC offset fixed was there?? DOH again!!

Well it's now had all functions and calibration checked and works just great so I've removed the old cal stickers, given it a clean, replaced the missing rubber feet, fitted working festoon lamps above the meter and it now proudly joins the other B&K gear on my bench

Last edited by Jez1234; 9th Apr 2021 at 5:09 pm.
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Old 9th Apr 2021, 5:10 pm   #2
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Default Re: Bruel and Kjaer 2610 Measuring Amplifier

Maybe a mod could correct the 7 to & in the title. Oops.
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Old 9th Apr 2021, 5:15 pm   #3
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Default Re: Bruel and Kjaer 2610 Measuring Amplifier

Congratulations! - and you have my sympathy Jez. There are various eccentricities in vintage B&K instruments and finding documentation can be like seeking hens' teeth! Many of their instruments are also designed and built in a way that tells us they never expected them to need repair.

Still, it's satisfying to have got it sorted and calibrated.

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Old 9th Apr 2021, 6:34 pm   #4
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Default Re: Bruel and Kjaer 2610 Measuring Amplifier

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... but all my experience was telling me that no instrument in working order pegs its needle like that....
Well, now you know! zero signal is -infinity dB on whatever scale.

But there are some instruments which are pegged left even with power off. These have scales with dB marked linearly across the sweep. Instead of electronics doing the logarithmic conversion, it's done in the movement by shaped pole pieces, and the spring forces the pointer far off-scale to the left.

They just sit there and look at you, looking broken. They've conned quite a few people.

HP used them in their acoustic and phone line gear. At South Queensferry we built the 'Psophometer' which had a Bell System weighting frequency response which Bell called 'Psophometric weighting'. Inevitably, it was referred to colloquially as the P***-off meter.

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Old 9th Apr 2021, 6:52 pm   #5
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Default Re: Bruel and Kjaer 2610 Measuring Amplifier

Oh they are certainly eccentric! I mean what's wrong with BNC connectors that they felt the need to design their own plug and socket arrangement that's compatible with nothing else?

Superb test gear though and up there with HP, Tek, Marconi Instruments etc.

If I can fathom why I might need a Psophometer.... (indeed precisely what one actually does beyond being "some sort of AC voltmeter for signal/noise testing"... and why the hell it has a switch for "Q-RMS/Peak"? A strange beast!) I have a 2429 that according to a sticker on it is noisy.

Amongst further B&K kit there's a 1/3rd octave filter bank that could be useful but a brief glance inside 20 years ago revealed that it seems to be a "build yourself a B&K filter bank self assembly kit"! IIRC all the thick film filter modules had been de-soldered, all the cables disconnected, all the plug in boards unplugged, all the switches removed and then the lot just bunged inside and the lid screwed back on! A lot of work to find out what was so wrong with it for this to have been done to it...

A Tek scope from the same source was "fun".... A 475 or 485 (can't remember and can't be bothered to look for it) that was very non functional. After a couple of days work I'd bodged new PSU smoothing caps that were never meant to fit into place, changed several out of spec or high ESR electrolytics and a few S/C tants and their series resistors and hey presto, a sharp, well focused display and all functions seemingly A1... until I came to trying other positions of the main timebase control and found it only worked at all in a few positions. Well I traced it to the switch board itself, removed it and opened up the switch chamber...OMG! Some of the gold plated switch "fingers" had been snapped off altogether... the best bit though was a small piece of paper about an inch square I found inside the switch chamber which simply said "sorry" on it!! Argh! It's sat in disgrace in some or other cupboard ever since.
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Old 9th Apr 2021, 6:56 pm   #6
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Default Re: Bruel and Kjaer 2610 Measuring Amplifier

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Originally Posted by Jez1234 View Post
... but all my experience was telling me that no instrument in working order pegs its needle like that....
Well, now you know! zero signal is -infinity dB on whatever scale.

But there are some instruments which are pegged left even with power off. These have scales with dB marked linearly across the sweep. Instead of electronics doing the logarithmic conversion, it's done in the movement by shaped pole pieces, and the spring forces the pointer far off-scale to the left.

They just sit there and look at you, looking broken. They've conned quite a few people.

HP used them in their acoustic and phone line gear. At South Queensferry we built the 'Psophometer' which had a Bell System weighting frequency response which Bell called 'Psophometric weighting'. Inevitably, it was referred to colloquially as the P***-off meter.

David
Aha! Hadn't seen your reply David when I posted the bit about "what the hell does a Psophometer do anyway?". You must be psychic! Has to be one of the most obscure items of test gear...
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Old 9th Apr 2021, 8:30 pm   #7
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Default Re: Bruel and Kjaer 2610 Measuring Amplifier

And there I was thinking you were very refined calling it by its proper name, when all along you hadn't yet read my reply spilling the beans on its nickname.

Psophometric was the frequency response shaping for noise measurements on the Bell phone system. Europe used one of the CCITT weightings.

In the line of 'What noise annoys an oyster' these weightings are to take account of the non flatness of the annoyance to humans of background noise. So the audio signal passes through the weighting filter, gets rectified and operates a meter, the scaling telling you how ****ed-off (in decibels) an average human will be on hearing it. So the nick name is doubly appropriate.

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Old 9th Apr 2021, 8:41 pm   #8
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Default Re: Bruel and Kjaer 2610 Measuring Amplifier

Quote:
Originally Posted by Radio Wrangler View Post
Quote:
Originally Posted by Jez1234 View Post
... but all my experience was telling me that no instrument in working order pegs its needle like that....
Well, now you know! zero signal is -infinity dB on whatever scale.

But there are some instruments which are pegged left even with power off. These have scales with dB marked linearly across the sweep. Instead of electronics doing the logarithmic conversion, it's done in the movement by shaped pole pieces, and the spring forces the pointer far off-scale to the left.

They just sit there and look at you, looking broken. They've conned quite a few people.

HP used them in their acoustic and phone line gear. At South Queensferry we built the 'Psophometer' which had a Bell System weighting frequency response which Bell called 'Psophometric weighting'. Inevitably, it was referred to colloquially as the P***-off meter.

David
I've got a HP 3400A here with a log scale for dB (the zero adjust is blanked off) and it does stay to the left with no power, unfortunately it now needs a lot of work as the front got smashed in on it's journey here, the casing for the meter movement is very broken inside, one day I'll have a look to see if it can be transplanted into another casing, or if it's beyond repair.
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Old 9th Apr 2021, 10:12 pm   #9
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Default Re: Bruel and Kjaer 2610 Measuring Amplifier

I'm quite jealous of this - I used to work in noise and vibration, and these were really useful bits of gear, even into the times when your signal would subsequently disappear into am A-to-D and some kind of software analyser. I expect you know that the 2610 (and I think the earlier 2606) can use interchangeable scales, and the meter hinges out to allow you to change them. The LEDs behind the scale plate light up little windows which allow you to work out what is going on, with whichever scale plate.

Not having one, I'm working on a 2209 SLM, which should be persuadable to behave the same way as a high-impedance signal amplifier. I have four and none of them so far work properly

I have a bunch of B&K spares - mic extension cables (but no mics and preamps, surprise surprise!), 7-pin mic plugs, B&K jack plugs, the odd manual and a few of those interchangeable meter scales. If anyone needs anything feel free to ask by PM - if I've got it surplus, it can join the normal charity sell-up I do.

cheers
Mark
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Old 9th Apr 2021, 10:30 pm   #10
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Default Re: Bruel and Kjaer 2610 Measuring Amplifier

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... HP used them in their acoustic and phone line gear. At South Queensferry we built the 'Psophometer' ...
My HP8903A has a 'Psoph' filter button on it. I don't think I've ever pressed it, and now I don't think I ever will .

Cheers,

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Old 10th Apr 2021, 1:04 pm   #11
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Default Re: Bruel and Kjaer 2610 Measuring Amplifier

I've got CCITT in an 8903B, along with 400Hz highpass. These filters were optional, so you could get all sorts of combinations.

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Old 10th Apr 2021, 3:42 pm   #12
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Default Re: Bruel and Kjaer 2610 Measuring Amplifier

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I'm quite jealous of this - I used to work in noise and vibration, and these were really useful bits of gear, even into the times when your signal would subsequently disappear into am A-to-D and some kind of software analyser. I expect you know that the 2610 (and I think the earlier 2606) can use interchangeable scales, and the meter hinges out to allow you to change them. The LEDs behind the scale plate light up little windows which allow you to work out what is going on, with whichever scale plate.

Not having one, I'm working on a 2209 SLM, which should be persuadable to behave the same way as a high-impedance signal amplifier. I have four and none of them so far work properly

I have a bunch of B&K spares - mic extension cables (but no mics and preamps, surprise surprise!), 7-pin mic plugs, B&K jack plugs, the odd manual and a few of those interchangeable meter scales. If anyone needs anything feel free to ask by PM - if I've got it surplus, it can join the normal charity sell-up I do.

cheers
Mark
That's the one yep. I only have the "standard" meter scale, "linear in dB" type for the 2610.
Also have the earlier and even more "all singing and dancing" 2607 which has B, C and D weighting available as well as the A weighting of the 2610 and the 2609, the latter has been my stalwart AF measuring amp since I got, fixed and calibrated it. The 2607 has the standard SA0051 meter scale and again I have no others for it. This one is linear on voltage and has usual squashed scale for dB but the unit can be switched to Log or Lin, unlike the later 2610, and originally would have been delivered with meter scales for both. It's many years since I tried the 2607... have it on the bench right now to try later on, whilst I'm in a B&K frame of mind IIRC it kinda works but a couple of the features don't or are out of cal. Unlike the mainly op amp and 4000 series CMOS 2610 the 2607 is pretty much all discrete and hideously complicated and as I'd long ago sorted the 2609 it has sat there for years untouched...

Together with the 1023 sine generator the 2609 has proved most useful in testing the phono stages I make for noise and RIAA accuracy (via a reverse RIAA network). Also at the R&D stage I've used the 2609 as the output section of a much lower noise and higher gain set up with a balanced input <1nV/rt/Hz home brewed pre amp before it and its AC output feeding one channel of a scope to see what the noise looks like... not all noises are created equal so seeing it's spikyness etc helps!

I had a beautifully serendipitous event with the fixing of the 1023 sine generator actually! When I was around 15 years old I had passed on to me by a friends father who was an electrical engineer a sample pack of two Beckman "Nixie tube" type displays that some rep had given him. Now although these work like Nixie tubes they were much more modern and miniaturised and look more like large LED 7 segment displays with glass fronts. I never had any use for these but being a hoarder...
Well I'll go to the top of our stairs but the B&K 1023, which amongst other issues had two duff digits in the display, only used exactly these display devices which I'd kept for 35 years!!
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Old 10th Apr 2021, 6:50 pm   #13
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Default Re: Bruel and Kjaer 2610 Measuring Amplifier

That's fantastic - I really like that kind of serendipitous thing. We never had one of those sine generators (we had a bunch of more ancient B&K BFOs and mic amplifiers in BIG boxes which all ended up in a skip, I'm sad to say) but we did have a couple of B&K phase meters which used the same display elements, I think. I'd be surprised if they have not hit the skip by now, and I'm not often along there where I used to work in order to find out what is being thrown out. [On the offchance you have use for a Norsonic 830, I have one in the current charity sellup - got to try when you meet someone else with such wierd interests ].
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Old 10th Apr 2021, 8:17 pm   #14
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That's such a disaster those old B&K items ending up in a skip!! The old stand-up vertical valve stuff with polished wood surrounds was really fabulous. Build quality to give Tek scopes of the day something to worry about!

The Norsonic will be a bit too full of digital unobtainium etc for me... I've been there before... I've got what should be pretty much the ultimate in LCR meters, the Genrad Digibridge, which has been giving me the V's every time I walk past it for years 'cos it has ROM's and PROM's etc, no doubt one of which is corrupted... and probably winning the lottery will be more likely than it ever working again!
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Old 10th Apr 2021, 9:06 pm   #15
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Default Re: Bruel and Kjaer 2610 Measuring Amplifier

I know what you mean about the 830 - though you never know, someone here may have hoarded just the right (programmed) EPROM for your bridge . I like the older stuff too. When I said I didn't have a measuring amp, I had forgotten that I kept one of these

https://picclick.co.uk/Bruel-Kjaer-T...134795906.html

- much less useful as an instrument than the 830, but it lights up lovely. From memory it looks like it behaves pretty much the same as the later measuring amps like yours (with the addition of a filter set, obviously) - I ought to drag it out and use it. I guess it will be full of valves, and will warm the room!

(By the way, I worked in acoustics for more than 25 years, and I never did find a use for B,C or D weighting - I have a vague memory that 'C' might have been to do with impulse noise and 'D' to do with aircraft, or the other way around. Colleagues had worked on gunnery noise and Concorde, but all my work was 'A' or nothing!)
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Old 10th Apr 2021, 10:00 pm   #16
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That's fantastic - I really like that kind of serendipitous thing. We never had one of those sine generators (we had a bunch of more ancient B&K BFOs and mic amplifiers in BIG boxes which all ended up in a skip, I'm sad to say) but we did have a couple of B&K phase meters which used the same display elements, I think. I'd be surprised if they have not hit the skip by now, and I'm not often along there where I used to work in order to find out what is being thrown out. [On the offchance you have use for a Norsonic 830, I have one in the current charity sellup - got to try when you meet someone else with such wierd interests ].
I think "look mum no computer" on youtube would have emptied that skip if he had known about them, he seems to have a wall of older B&K stuff. Certain old test gear seems to be in demand for making electronic music the old fashioned way.

David
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Old 10th Apr 2021, 10:32 pm   #17
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I know what you mean about the 830 - though you never know, someone here may have hoarded just the right (programmed) EPROM for your bridge . I like the older stuff too. When I said I didn't have a measuring amp, I had forgotten that I kept one of these

https://picclick.co.uk/Bruel-Kjaer-T...134795906.html

- much less useful as an instrument than the 830, but it lights up lovely. From memory it looks like it behaves pretty much the same as the later measuring amps like yours (with the addition of a filter set, obviously) - I ought to drag it out and use it. I guess it will be full of valves, and will warm the room!

(By the way, I worked in acoustics for more than 25 years, and I never did find a use for B,C or D weighting - I have a vague memory that 'C' might have been to do with impulse noise and 'D' to do with aircraft, or the other way around. Colleagues had worked on gunnery noise and Concorde, but all my work was 'A' or nothing!)
Now that 2113 is the biz! Lovely

I've also never needed more than A weighting... in fact I noticed in a B&K brochure that "the proposed new D weighting is included"... Hmm...

I powered up that 2607 and it is not looking good to put it mildly! I can't find anything working correctly in fact! I see what you mean about them not thinking it could need repairing, in as much as it has maybe 20 plug in PCB's, non of which can be accessed for servicing in situ. Virtually impossible to service then without jigs to provide rail voltages and connections to the outside world to mimic use when fitted to the unit. I can't see this one getting repaired but will prob at least check out all rails are present and correct.
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Old 10th Apr 2021, 10:48 pm   #18
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Default Re: Bruel and Kjaer 2610 Measuring Amplifier

I once knew a lot more about acoustics, than I ever did about electronics (where, in company here, I have 'L' plates on). So you'll have a much better chance with the 2607 than I ever would!

The 2113 would have been used back in the lab (when dinosaurs roamed the earth) with a SLM into a tape recorder on site - an older colleague had a collection of data recorders, from Ferrographs through Uhers, to a Store 4 I sold on here, to Nagras, then Pro Walkmans, to portable DAT at the end. Somewhere around the Nagra-Walkman era, lab based digital FFT became a thing and the 2113 would have gone into a cupboard. Though sometimes the lab gear went out on site - a colleague remembered taking an OnoSokki 900 (I kept two of them too - digital or not, they're really great to use ) up a precarious ladder, at a time when it cost more than his house...
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Old 11th Apr 2021, 1:42 am   #19
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I once knew a lot more about acoustics, than I ever did about electronics (where, in company here, I have 'L' plates on). So you'll have a much better chance with the 2607 than I ever would!

The 2113 would have been used back in the lab (when dinosaurs roamed the earth) with a SLM into a tape recorder on site - an older colleague had a collection of data recorders, from Ferrographs through Uhers, to a Store 4 I sold on here, to Nagras, then Pro Walkmans, to portable DAT at the end. Somewhere around the Nagra-Walkman era, lab based digital FFT became a thing and the 2113 would have gone into a cupboard. Though sometimes the lab gear went out on site - a colleague remembered taking an OnoSokki 900 (I kept two of them too - digital or not, they're really great to use ) up a precarious ladder, at a time when it cost more than his house...
Hi Fi gear here, so electronics but well crossing over with acoustics dabblings Have a series 7 Ferrograph that worked A1 when it was last switched on.... 15 years or so ago! Nagras are of course cheap nasty crap that needs disposing of properly and if you have any laying around you should send them to me so I can take them to the skip for you
Would Nicolet Scientific be foul language I wonder? Mini-Ubiquitous FFT Analyser... a story for another day I think... if this was the Mini one then I hate to think how big the normal one was!
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Old 11th Apr 2021, 2:38 am   #20
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Default Re: Bruel and Kjaer 2610 Measuring Amplifier

We're not going to have the Nagra versus Stellavox wars are we? The one no-one can afford to fight.

I see Kudelski are still on the go but have gone cultist/boutique.

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