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The Vintage Audio section / Re: 84 y.o. Pilot restoration
« Last post by Steerpike on Today at 01:02:34 AM »
Turns out it had been gutted and had modern junk inside.

That is so nasty - I hate seeing that, and it happens too often.
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General Discussion / Re: Do you also see evidence of fraud here?
« Last post by Steerpike on Today at 12:57:35 AM »
Reminds me when CD's first came on to the scene and all speakers manufacturers were saying that their speakers were "Digital Ready" wtf, :facepalm: since when is a driver digital anything. You could not get anything more analogue.

Philips DID make a digital loudspeaker... not a commercial product, but a few as a laboratory exercise:
The voice coil has 16 taps on it - so it behaves like the R-2R ladder in the D/A converter.
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Valves/Tubes / Re: 100 watt push-pull fixed bias amplifier
« Last post by Ampdog on Today at 12:47:32 AM »
The OPT's do not have 16ohmm output taps, so the C12/13 network will have to adjusted. I have 4 ohm and 8 ohm though. Do you have any idea how to adjust R22 and R23 accordingly?

Karel,

Apology! I seem to have missed this question.

The winding ratio between 16 ohm and 8 ohm is 1.414, thus R22 + R23 will have to be decreased  to 70,7%, giving 4,2K total resistance.  If one stays with the feedback via C12 to the 4 ohm output winding, then R23 becomes about 2,2K, with R22 remaining at 3K. (R23 now connected to your 8 ohm output.)

But the values of C12, C13  are entirely a function of the OPT characteristics. They work in the supersonic region, to compensate for OPT internal capacitance and leakage reactance (thus phase correctors.)  Their effect for that particular OPT is somewhere >60 KHz and certainly cannot be trimmed by hearing.  Thus I cannot recommend values for your OPT; to get those right one will need a square wave generator and oscilloscope to check. 

Also the necessity of C12 might indicate some inequality between secondary sections of the particular OPT; ???  I have always just used a single RC feedback combination from the whole secondary, but that is with using all secondary windings for both 8 ohm and 4 ohm outputs (for three secondary sections the usual 30% - 40% - 30%  secondary winding segmentation).


P.S:  Despite Dr Gillespie's remark that his design is stable, I would still add a 680 ohm 5W resistor over the secondaries just to assure stability without a load. (I do this in all my valve designs. Stray capacitance for point-to-point wiring will always differ from model to model.)
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I agree with John Cleese's conclusion about experts at the end of the 2nd bit.

https://www.youtube.com/watch?v=LdZFmeMWrtk&feature=youtu.be
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Open Talk / Re: What is This?
« Last post by Telephono on Yesterday at 11:21:23 PM »
Thanks for the info!
I figured it was probably burgled and discarded.

Likely so.

Or someone tossed it after the original owner passed away. Many Masonic items end up in the dump or backyard fire - usually through a mix of ignorance, fear and misplaced religious zeal on the part of family members.

Please do try to reconnect it with a local lodge, it looks like it was hand-made by someone and presented to a lodge member as a gift. The name inside the box should make finding its original home quite easy.

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Open Talk / Re: Earth leakage kept tripping
« Last post by VALVAGLO on Yesterday at 10:53:27 PM »
My well meaning domestic regularly spills water as she fills the steam iron.  POP goes the earth leakage.
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General Discussion / Re: Where can I find speaker wall plates in SA?
« Last post by Hi-Phibian on Yesterday at 10:06:51 PM »
Used to be quite a standard thing with the multi room kit. 
Would think elan control 4 niles should all be able to offer these through their local channels.
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AV Items: For sale / Re: 2m audioquest rockefeller
« Last post by geo on Yesterday at 10:01:47 PM »
Single cable used for center channel and bi-wired 36v Dbs can be upgraded to 72v
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Have a listen to the Bentley Acoustics as well. Very well priced for the speakers you get.
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Computers & Networking / Re: 7.1 gaming headsets. What's up with that?
« Last post by kalgat on Yesterday at 09:59:20 PM »
I have a pair of these, which have 10 discreet drivers vs others which fake it with witchcraft

https://www.asus.com/za/Headphones-Headsets/STRIX_71/

The spatial sound is very good but not worth the price and not required (if the enemy is above you were dead anyway)

Here is a recent top 15 list from techradar https://www.techradar.com/news/computing-components/best-pc-gaming-headset-1322675 which might help you find the best bang for buck
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