6B4G - The Resurrection Shuffle

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Cressy Snr
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#151 Re: 6B4G - The Resurrection Shuffle

Post by Cressy Snr »

OK, after much havering and deliberating, a decision has been made.
I'm not prepared to go ahead with the project as it stands, It's far too heavy and complex.

I have not given it up, but there is scope for considerable simplification and weight shedding.
Looking at those pentode curves, generated on Nick's uTester, it seems pretty obvious to me that the reason the original iteration of this amplifier sounded so good, was down to the driver, rather than the fact that there was a 6B4G in the output stage.

I'll get going this week on the chassis punching and the mounting of sockets and iron. Events this last week, mean that I now know that this is the last valve amp that will come out of the ends of my fingers. Speakers will be the thing I'll be concentrating on after this.

The valve amp is now a pure romance/nostalgia project. It will come to Owston along with the large Omnis and a point and squirt speaker based on Dave Dlugos' (Planet10) Mileva and Demitri, which came out of the original 2006 Metronome collaboration; same drivers, same TL loading but completely different philosophies. We can have fun comparing.
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IslandPink
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#152 Re: 6B4G - The Resurrection Shuffle

Post by IslandPink »

Cressy Snr wrote: Sun Sep 10, 2017 10:38 pm the reason the original iteration of this amplifier sounded so good, was down to the driver, rather than the fact that there was a 6B4G in the output stage.
..and they were 1953 Sylvania 6B4G's and the power supply was Ace ...
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Cressy Snr
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#153 Re: 6B4G - The Resurrection Shuffle

Post by Cressy Snr »

IslandPink wrote: Sun Sep 10, 2017 10:40 pm
Cressy Snr wrote: Sun Sep 10, 2017 10:38 pm the reason the original iteration of this amplifier sounded so good, was down to the driver, rather than the fact that there was a 6B4G in the output stage.
...and the power supply was Ace ...
Prcisely and that PSU is where it is headed again, but with all the additional advantages of the stuff I've learned since then. :D

At this stage of the evolution of my DIY career it is speakers, where the mileage for system improvement is greatest. That has become very clear over the course of the last week.

Chassis is ready. Stand by for holes. 8)
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#154 Re: 6B4G - The Resurrection Shuffle

Post by IslandPink »

Cressy Snr wrote: Sun Sep 10, 2017 10:43 pmAt this stage of the evolution of my DIY career it is speakers, where the mileage for system improvement is greatest. That has become very clear over the course of the last week.
No arguments on that one :D
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Cressy Snr
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#155 Re: 6B4G - The Resurrection Shuffle

Post by Cressy Snr »

Right!
Got one possible layout:
Image

Front row,
Centre two valves are the PCL 86 shunt regs: one for each of the two outer 12GN7 pentode drivers.

Back row,
Large valve between the two JJ 2A340 is the 6336A series pass valve for the power stage regulator.
Two valves behind the series pass valve are the 6AU6 error amp and the 0B2 VR tube voltage reference.
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#156 Re: 6B4G - The Resurrection Shuffle

Post by steve s »

Nice to see it moving on Steve...
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number
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jack
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#157 Re: 6B4G - The Resurrection Shuffle

Post by jack »

steve s wrote: Wed Sep 13, 2017 9:21 pm Nice to see it moving on Steve...
Indeed. Loads of fun!
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#158 Re: 6B4G - The Resurrection Shuffle

Post by jack »

simon wrote: Tue Aug 22, 2017 8:14 pm Merlin Blencoe's power supply book is out of print now (seen Jack is looking for a copy on DIYAudio) but Merlin once posted it was because there were so many errors in it he wasn't happy with it. I'm sure most of it is just fine, but that comment alone has made me a little uneasy about its content. That said there's little new in the valve world so there should be corroborating text elsewhere.
I just found this on his website:
http://www.valvewizard.co.uk/ wrote:15 November 2013: I've been getting a lot of mail about my power supplies book. I'm sorry to say I permanently removed it from print. It contained too many mistakes and typos, and it didn't match the style of my preamp books. Do not email me asking if I have spare copies or PDFs; your email will be ignored. Fortunately, all the best material from the power supply book can now be found in the final chapter of my hi-fi preamps book!
(my highlighting)
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#159 Re: 6B4G - The Resurrection Shuffle

Post by IslandPink »

Oooh Errr !
Anyway, nice to see progress Steve - I need inspiration for what I need to make as the 4-channel amp now, for the OB speakers. Putting it off, but seeing a metal box with bulbs and transformers sticking out of it can only help.
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#160 Re: 6B4G - The Resurrection Shuffle

Post by simon »

That's good to know Jack
Cressy Snr
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#161 Re: 6B4G - The Resurrection Shuffle

Post by Cressy Snr »

Need a few resistors and caps ordered.
Commissioned Ant to make a 20 x 14 x 4" high oak case with 2mm ally top plate.
It'll go quiet for a while now.
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#162 Re: 6B4G - The Resurrection Shuffle

Post by jack »

Just for the hell of it, I modelled the shunt regulator in LTspiceXVIII using Derk Reefman models generated from real valves analysed by uTracer then processed by ExtractModel as described in http://www.dos4ever.com/uTracer3/uTracer3_pag14.html

These models are not theoretical - they are generated from actual tubes of the type you need - in the case of valves with multiple sections, multiple models are generated - they are very accurate, far better than purely theoretical models - with a 100mA load, I get about 341V out...

The available model library is now pretty extensive and contains most of the normal valves we use. One interesting thing he points out is that triode-strapped pentodes/tetrodes do not behave as the normal pentode/tetrode model with its pins joined up - there are separate models again for those cases.

The reg seems pretty good, though I want to do modelling with variable loading, e.g. step response, rather than just ripple on the input which it seems to remove pretty accurately - with 4V ripple on the input (1%) there was only 100mV ripple on Vout (0.03%)...
Reg.png
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Cressy Snr
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#163 Re: 6B4G - The Resurrection Shuffle

Post by Cressy Snr »

Nice to know the theory is borne out in practice. :)
Cheers Nick.

I'm going to have to go back to my orignal timetable for this project, which was to start it in the new year. So it's now put back until the end of January at the earliest.
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Cressy Snr
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#164 Re: 6B4G - The Resurrection Shuffle

Post by Cressy Snr »

Been thinking a bit more about this project and I'm afraid I've come to the conclusion that it is nothing more than a nostalgia exercise. I really can't justify forking money out on something that my heart is not really in. Had this discussion at Steve's place a couple of Fridays ago and there's just no point in doing a build of something I'm no longer interested in. I really can't be arsed.

I realise that this may be disappointing for some of us, but I've done more than enough projects over the years and I've reached the point where I'm happy with what the system is doing. The solid state pre/power amp and the phono stage simply sound lovely with my speakers and with the addition of the Goldring E3 phono cartridge, I have something quite special, that ticks all the boxes on my mental list of what a music system ought to sound like.

My main DIY interest now lies in omnidirectional and semi/omnidirectional loudspeakers, combined with quarter-wave bass loading, and of course my long running Metronome concept for direct radiator setups. So rather than be hopping from one thing to another, I've decided to impose some sorely needed focus on my efforts.
Of course anyone else is welcome to build it and I have all the valves, except the 6B4Gs (Andrew L has those) I do have an unused brand new pair of JJ 2A3-40 for a reasonable price, which I reckon would be sh*t hot in this amp.
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#165 Re: 6B4G - The Resurrection Shuffle

Post by jack »

Completely understand - it's a MASSIVE commitment.

Shame really, as you say, for the rest of us, as it's a great project (in every way) and the original thread is now a bit of a "shadow" of its former self...

If you can dig out the final schematics, at upload them to the forum (as opposed to using an external hosting server), then at least they're preserved here...

Cheers!
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