Remember These?

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Nick
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#436 Re: Remember These?

Post by Nick »

They also have a habit of dying from static is you go too close to them.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
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Nick
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#437 Re: Remember These?

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Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
Cressy Snr
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#438 Re: Remember These?

Post by Cressy Snr »

That's a beast :shock:

At least the 783 does in theory work as a starting point for further experiment.
Ray and me have been toying with the idea of a mosfet CCS kit from the USA once we've got the amps going in our respective proper boxes, but that IXYS thing looks just the job for future improvement.I for one would probably need a bit of help to make it work though. :)
There's probably a great deal of untapped potential lurking in these single tube OTLs, a potential that a bog standard Lazy Man's constant current sink won't quite let out. Nevertheless the 13E1 OTL does, on the breadboard at least, sound fantastic.
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Ray P
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#439 Re: Remember These?

Post by Ray P »

I've already taken delivery of a pair of the K&K Audio current sinks and have been working to be able to easily install them in my build. They're based around these Mosfets - FQH8N100C.

The webpage with information about the boards, part way down here;

http://www.kandkaudio.com/other-kits/

mentions them being tested to 400mA but I've exchanged mails with Kevin at K&K and he's confident that they'll be fine at 500mA as long as the heatsink is big enough. The only complication is that the voltage at the cathode that we'll be working with is too low for its onboard voltage reference to operate so I plan to hook it up to my B+ supply via a dropper resistor - it's a simple mod that's detailed in the kit documentation. Let me know if you want to know more.
Sorry, I couldn't resist!
Cressy Snr
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#440 Re: Remember These?

Post by Cressy Snr »

Cheers Ray.
I'm starting to feel that this bloody thing is taking on a life of its own and soon there are going to have to be some choices made pretty sharpish and stuck to, or it'll never get boxed. :lol:
Sgt. Baker started talkin’ with a Bullhorn in his hand.
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Mike H
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#441 Re: Remember These?

Post by Mike H »

Cressy Snr wrote: Tue Feb 12, 2019 3:02 pm That's a beast :shock:
Croly Hap. :shock:
 
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RhythMick
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#442 Re: Remember These?

Post by RhythMick »

Mike H wrote: Tue Feb 12, 2019 10:04 pm
Cressy Snr wrote: Tue Feb 12, 2019 3:02 pm That's a beast :shock:
Croly Hap. :shock:
Well said
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#443 Re: Remember These?

Post by Cressy Snr »

Cressy Snr wrote: Tue Feb 12, 2019 8:56 pm I'm starting to feel that this bloody thing is taking on a life of its own and soon there are going to have to be some choices made pretty sharpish and stuck to, or it'll never get boxed. :lol:
So, a choice has had to be made, and I've decided to use the LM317HVT/NOPB, 1.5A, 60V regulator IC in the 13E1 cathodes for now, and have ordered some. Although this may not be the best choice of cathode current sink componentry among the DIY OTL experts, it is the logical one for SS novices. It will work on a 4V drop, is as simple to use as the TL783 and will get me up and running without fuss. Fancier bits of silicon can always be tried later on by liasing with those who are more practiced in the dark arts. :)
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Ray P
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#444 Re: Remember These?

Post by Ray P »

Or you could look at the LM338 if you wanted something more robust, though it doesn't seem to be available in a HV version;

https://www.digikey.co.uk/product-detai ... -ND/212669

Also, at least in the short term, you might want to consider protecting the LM317 as per BR's modiifcation to the original 300B circuit - I can let you have the details if of interest. Wolfgang is of the view that the protection is detrimental to the sound but for peace of mind maybe worth a try - could always be removed later. I use the protection arond the 'TL783s in the 300B SE-OTL amps I bought to Owston.

I think I might just go straight for the K&K current sinks in my build and see how they work out.

I should also dig out my copy of BRs book, Tubes and Circuits, that published the initial 300B circuit and see what he says about the current sink aspect of the design. I can recall mention of it necessitating AC filament supplies for the 300Bs, but we're not dealing with a DHT with the 13E1 so the considerations will be different.
Sorry, I couldn't resist!
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#445 Re: Remember These?

Post by Cressy Snr »

My LM317HVs have shipped, so I should have them tomorrow,

The Texas Instruments LM317-HV, has on-board, safe area, current limit, thermal overload protection, that "makes the device blowout proof" and the protection functions operate even if the adjust terminal becomes disconnected, so says the datasheet at least. The LM317HV is nearly four times the cost of the vanilla LM317T, so hopefully it will work nice and safe in the cathodes of the 13E1.

Yes, in "Tubes and Circuits," Bruce does mention that usage of the LM317T in the 300B amp precludes the use of DC filaments.
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#446 Re: Remember These?

Post by Cressy Snr »

Now I've made a firm decision about which way to go with the OTL and all the components are here, I can start the thing.

The box is the first thing on the agenda and is of the 'wood surround' type, with aluminium top plate. Apertures will be cut in the front and back faces of the box to house stainless steel panels that will carry the IEC inlet, mains fuse holder, 5 phono inputs and a pair of speaker outlets on the back. Power on switch, HT on switch, indicator light, source selector and volume control will be on the front stainless steel panel insert.

The top plate is in two pieces. The lower piece will have all the bits bolted to it. Mains and 25V heater toroids go on top, chokes, caps and 6H30pi DC heater board etc underneath. The two top mounted toroids will enclosed under cylindrical housings made from sprayed up round cake tins. 13E1 sockets will be mounted on circular chrome steel fan guards so that air can flow up from below. There will be a second top plate in order to hide the bolt heads and give a nice finish. I'm currently looking at a light powder blue gloss finish for the top plate and transformer housings. With the chrome of the fan guards and the stainless panel inserts, we should get a nice retro vibe.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
Cressy Snr
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#447 Re: Remember These?

Post by Cressy Snr »

I've cut the four sides for the box out of MDF....er that's it. :roll:
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Ray P
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#448 Re: Remember These?

Post by Ray P »

It's a start Steve! :)
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IslandPink
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#449 Re: Remember These?

Post by IslandPink »

I haven't done anything since Saturday ... but this weekend will be different !
"Once you find out ... the Circumstances ; then you can go out"
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Ali Tait
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#450 Re: Remember These?

Post by Ali Tait »

Yeah c’mon Mark, wanna hear it in stereo!
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