6C33C SE-OTL Project

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IslandPink
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#31 Re: 6C33C SE-OTL Project

Post by IslandPink »

Very very interesting ...
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Ray P
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#32 Re: 6C33C SE-OTL Project

Post by Ray P »

I'm working on my own build of this 6C33C SE-OTL amp, though I'm rather slower than Wolfgang...

I plan to use a regulated supply for the 6SN7 stage, specifically a Neurochrome Maida regulator that I have available.

https://www.neurochrome.com/21st-centur ... r-rev-2-0/

The obvious approach for the 6C33C B+ supply is to use the same CLCLC approach as Wolfgang but I keep wondering about using a couple more Neurochrome regulators here as well. Bearing in mind that the design uses a current sink on the cathode of the 6C33Cs I would welcome any views/comments/observations from the panel about this option?

Ta
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#33 Re: 6C33C SE-OTL Project

Post by Wolfgang »

Maybe it's easier to find the right answers, Ray, if we reformulate the question a little?

What goal(s) do you want to achieve using two regulators for the 6C33?

Is it rather an aesthetic issue that you don't like to work with clumsy chokes and big caps or are you concerned about how mains voltage fluctuations could negatively impact the sound (must be pretty bad over there as I have read recently, up to +/- 10V)?
All issues around the 6C33 like less distortion, absolute stable Ip etc have already been taken care with the CCS. In this respect another regulation process could only negatively impact the CCS unless it's completely out of its way (set to 1A or more).

Mains voltage fluctuation would however heavily impact the AC heaters of the 6C3 if you don't use a very oversized transformer. (didn't try this so I couldn't tell what size would work).
With 50VA per tube it gets exactly 12,6V at 120V. At 118V it's already 12,4V which sounds actually even better IMO! I stabilize my mains voltage with a PS audio Power Plant as we have mains fluctuations between 3 to 7V.

With CCS the voltage drop of the B+ psu is 20V and this is pretty immune against minor mains voltage fluctuations. If I remember correctly +/- 3-5V change with the Variac didn't affect the B+ voltage at all.
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#34 Re: 6C33C SE-OTL Project

Post by RhythMick »

Ray P wrote: Wed Jun 06, 2018 9:30 pm I'm working on my own build of this 6C33C SE-OTL amp, though I'm rather slower than Wolfgang...

I plan to use a regulated supply for the 6SN7 stage, specifically a Neurochrome Maida regulator that I have available.

https://www.neurochrome.com/21st-centur ... r-rev-2-0/

The obvious approach for the 6C33C B+ supply is to use the same CLCLC approach as Wolfgang but I keep wondering about using a couple more Neurochrome regulators here as well. Bearing in mind that the design uses a current sink on the cathode of the 6C33Cs I would welcome any views/comments/observations from the panel about this option?

Ta
My view is that if you change the power supply you change the amp. Maybe that's what you want, but if you're aiming for the same result I wouldn't start by fundamentally changing the PSU.
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#35 Re: 6C33C SE-OTL Project

Post by Wolfgang »

And to change the sound of this amp as it is now would be such a loss as it exudes reality of music. Incredible dynamics, lightning fast transients against a pitch dark noise free background. It doesn’t get better and it seems to have limitless power. If I needed it to drive 8 ohm speakers I would simply add another 6C33 per channel . The only thing it really needs is a powerful preamp/buffer with gain to drive it. My #26 or my 2A3 buffer (single DHT with gain) for example are a perfect match. Driving it directly with the Soekris DAC was rather disappointing.
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Ray P
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#36 Re: 6C33C SE-OTL Project

Post by Ray P »

I haven't decided to use the Neurochrome regs for the 6C33Cs but just want to canvas some opinions/thoughts before I start spending on components.

My rationale for considering the Neurochromes has several aspects;
1. These regulators have a reputation for extremely good ripple rejection, and good music set against an inky black background.
2. As the 6C33Cs will be operating very close to the edge of their envelope fluctutions in mains voltage will increase the B+ voltage with a possible impact on reliability.

Should I choose to explore the Neurochrome regulator route I would configure them with a healthy peak current headroom, well above the constant load imposed by the current sink.
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Ray P
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#37 Re: 6C33C SE-OTL Project

Post by Ray P »

Wolfgang wrote: Fri Jun 08, 2018 8:39 pm And to change the sound of this amp as it is now would be such a loss...
Unless the change turns out to be a further improvement to the sound...
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#38 Re: 6C33C SE-OTL Project

Post by Wolfgang »

True but very hard to imagine from where I am sitting (sweet spot).

I think I should upload a recording so that everyone on this forum can get a picture what I am talking about.
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#39 Re: 6C33C SE-OTL Project

Post by Ray P »

I've been thinking further on the power supply options and another consideration with this particular amplifier is heat management and the neurochrome regulators would add to that issue if used with the 6C33Cs so, on reflection, I will take the low risk route and go with the CLCLC B+ supplies for the 6C33Cs, as per Wolfgang's build.

Heat is much less of an issue with the neurochrome regulator powering the 6SN7 pre-stage so I will stick with that.

That decided I can now push on with sorting out my chassis and ordering parts.
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#40 Re: 6C33C SE-OTL Project

Post by Ray P »

I've got a few days leave from work so I'm using the opportunity to work out a chassis layout and ordering parts.

The main issue to deal with is heat management due to the 6C33C filaments, 12V @ 3A, which results in a lot of localised heating, compounded by most Septar sockets having relatively poor contact arrangements.

I've managed to pick up some Johnson septar sockets from the US for a reasonable price - in his write-up on using 6C33Cs 'Romy' rates the Johnson sockets as much better than the Russian and Chinese sockets, which he suggests neeed periodic replacement.

I'm now working on how I can set out the chassis to try and dissipate the heat from the 6C33Cs and to prevent a general temperature rise inside the chassis that might shorten the life of other components (such as electrolytic caps). Lots of vent slots and careful placement of parts required. I'm also keeping the possibility of using a fan up my sleeve.

I'll post more info, and eventually some pictures, as I progress the project.
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Dave the bass
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#41 Re: 6C33C SE-OTL Project

Post by Dave the bass »

Ray P wrote: Tue Jul 03, 2018 11:42 am I'm also keeping the possibility of using a fan up my sleeve.
Won’t that just cause the hot air to blow up to your armpit?
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Nick
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#42 Re: 6C33C SE-OTL Project

Post by Nick »

Ray P wrote: Tue Jul 03, 2018 11:42 am I've got a few days leave from work so I'm using the opportunity to work out a chassis layout and ordering parts.

The main issue to deal with is heat management due to the 6C33C filaments, 12V @ 3A, which results in a lot of localised heating, compounded by most Septar sockets having relatively poor contact arrangements.
Remember that the dissipation from the valve will be the heater + the plate dissipation.

So something like 12 * 3 + 105 * 0.45 so 83W or so.
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Ray P
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#43 Re: 6C33C SE-OTL Project

Post by Ray P »

Nick wrote: Tue Jul 03, 2018 2:03 pm Remember that the dissipation from the valve will be the heater + the plate dissipation.
No, not forgotton and I'm making sure there will be plenty of vents to enable heat to be convected away.

The heat issue with the filaments is that it causes localised heating of the valve pins and socket connectors, and thence the ceramic base, so i'm paying attention to trying to thermally couple the ceramic base to the chassis...

As said before, I'm also giving myself the option of using a fan to increase airflow (into my armpit...). I'm just looking at 'silent' PC fans to work out how I could use them.
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#44 Re: 6C33C SE-OTL Project

Post by Ray P »

If I need to add fan cooling this looks as though it should do the job nicely;

https://www.quietpc.com/nf-a9-flx

Looks like it just needs a 12V supply and it ought to be possible to put together a switched speed controller by adapting the LNA cables.

Any thoughts/observations?
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#45 Re: 6C33C SE-OTL Project

Post by Ray P »

and its bigger brother;

https://www.quietpc.com/nf-s12a-flx
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