Big and shiny autumn amplifier

the thermionic watercooler

Big and shiny autumn amplifier

Postby Olof » Thu Sep 01, 2016 12:15 pm

September is here, so it is officially autumn and time for big and not properly thought through projects! I've been thinking on and off for a while about doing something with voltage regulation. I know common sense dictates that you design the output stage of the amplifier first, but I feel like starting in the other end. I want to build something with a tube regulated power supply, so that's where I'll start.

After looking at plenty of similar designs, this is what I've come up with:

20160901-194244.jpg
regulator
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A 6080 tube can pass plenty of current and since it's dual the two channels can be separated already at the power transformer. The ECC83 is also dual, and high gain enough to control the pass tube. The potentiometer sets the output comfortably to 250V-300V but can probably go a bit wider if the input voltage is not too far off or too close. I could claim that the 0B2 is chosen for stability and not the fancy color but well...

I've run some simulations in LTspice and it seems to work like I intend it to, with proper line and load regulation. The output should bee good enough to drive a pair of push-pull EL84 or maybe something even bigger.

Assuming there will be some slow days at work I will make this thing happen before the winter holidays. By then it will be cold and not a problem to light up a small army of tubes. (lol)

Any thoughts or advise is highly appreciated!

Olof
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Re: Big and shiny autumn amplifier

Postby Geek » Thu Sep 01, 2016 8:09 pm

Hi Olaf,

Simple regulators like that can give reasonable results.

But that "77K" on the ECC83 anode and 6080 grid... is that a typo? Making it no less than 470K will improve regulation big time.
(my Lambda lab-grade bench PSU uses 680K there)

If both 275V windings on the transformer are the same current, parallel them or use them in series with a FWCT rectifier setup for more efficient use of transformer VA and a cooler running unit.

Cheers!
-= Gregg =-
Fine wine comes in glass bottles, not plastic sacks. Therefore the finer electrons are also found in glass bottles.
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Re: Big and shiny autumn amplifier

Postby Olof » Fri Sep 02, 2016 12:58 am

Hi Geek, thanks for the input!

The 77k was just put there to give the ECC83 roughly 1mA, haven't poked around with it at all. I simulated the circuit just now with 470k and 680k instead, you are completely right, both line and load regulation is improved. So that's a keeper!

My though was to use the other 275V winding to the other channel with a copy of this circuit there as well, using the other halves of the 6080 and ECC83. I'm thinking this would give ridiculously good channel separation and as a bonus it would require two 0B2 tubes instead of one, twice the glow! The drawback is of course twice as many caps, coils and rectifiers as well...

Olof
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Re: Big and shiny autumn amplifier

Postby Geek » Fri Sep 02, 2016 4:11 am

That makes sense.

Logic says if the channel separation noticeably improves, that means the regulators suck - but I have personally heard the improvement in a "Dual Monoblock" design out of one PSU, tube and SS.

Look forward to the project being developed :))

Cheers!
-= Gregg =-
Fine wine comes in glass bottles, not plastic sacks. Therefore the finer electrons are also found in glass bottles.
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Re: Big and shiny autumn amplifier

Postby Olof » Tue Sep 06, 2016 1:16 am

I needed to do my homework on regulator tubes, so I got myself a bunch. These are the tubes I measured:

0C3small.jpg
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0B2small.jpg
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0A3small.jpg
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0A2small.jpg
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Out of these four, 0B2 and 0C3 performed better than the others with some margin. Here is what I got for them:

0C3measure.PNG
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0B2measure.PNG
0B2measure.PNG (13.87 KiB) Viewed 3053 times


Even though the 0C3 seems slightly better in performance, the 0B2 is much less bulky and way more shiny, so I will likely stick with my original plan of using 0B2!
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Re: Big and shiny autumn amplifier

Postby Olof » Thu Sep 08, 2016 8:26 am

All the tubes have arrived, things are taking shape! I did not fully realize how much bigger the 6080 was... can't wait to get that beast up and running!

I'm thinking the regulator (excluding the pi-filter from the transformer) should fit snugly on a 160x100mm prototype board. Still haven't decided what to do with the heaters, should they be elevated to one of the VR tubes as center tap? Will I need to strip away the pads not used on the board to avoid sparks?
layout regulator.jpg
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2016-09-08 14.32.22.jpg
2016-09-08 14.32.22.jpg (211.01 KiB) Viewed 2991 times
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Re: Big and shiny autumn amplifier

Postby Olof » Fri Sep 23, 2016 2:04 am

Transformer has arrived, now I'm only waiting for the big slow boat from china to bring me the sockets! I found some nice leftover ferrites at work which will do nicely as inductors. First one came out at 1.66H 45R, using exactly four sheets of high-tech insulation material (printer paper) for the air gap. There is still plenty of space left on the coil former, I might redo it with thicker wire for a lower resistance. Also might go for a narrower gap for higher inductance, but then I might risk saturating the core... I should probably do the math (lol) Anyone with experience on this?

20160922_184808.jpg
Winding inductor
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20160922_194437.jpg
1.66H
20160922_194437.jpg (138.75 KiB) Viewed 2871 times
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Re: Big and shiny autumn amplifier

Postby Olof » Thu Oct 06, 2016 7:50 am

What do you know, it worked without a single bang or puff of smoke! Haven't dared to actually push it, just checked the function. Shiny part achieved!

Now the question is what to do with it? A stereo-35? A Mullard 5-10?

IMG_6793small.JPG
IMG_6793small.JPG (235.33 KiB) Viewed 2771 times
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Re: Big and shiny autumn amplifier

Postby HK » Sat Aug 04, 2018 9:35 am

Well, kind Sir ... what became of this shiny project?

Inquiring minds like to learn. [:)
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