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Cornet 2 tube phono stage (~100KB)

post #1 of 32
Thread Starter 
For a while now, I've been wanting to build a vacuum tube phono stage. I looked long and hard at mainly three options: the Mapletree, the Bottlehead, and some of the Hagerman designs. They all look pretty good, and I did a lot of reading of various reviews... you know the drill. Settle on something and hope for the best. I ended up settling on the Hagerman Cornet2, which is an improved version of his original cornet, and includes some of the tweaks that builders of the original Cornet were adding.

Rather than going into a lot of specific detail on Jim's design, I'm just going to put up the link to the specifications. There is also a section where Jim Hagerman talks about his design philosophy. I always like reading those sorts of things, it gives you a nice insight into the designer, and talks about his or her preferences, goals, and anything else that is important to them in designing gear.

So I got the board and scrounged up some parts. I was able to use some from the parts bin, and others I bought specifically. The documentation does offer a complete list with part numbers for the standard build, but you can gather your bits from anywhere. The board took me two evenings to populate. The first night I did all the parts matching, the second night was soldering. The large coupling caps I ordered from Mike Percy, so he sent a matched pair.

I've been doing a little bit of casework this week, whenever I find a bit of time. I'd much rather dive in and spend a full day or two, going from start to finish, but between family and work, there is not much time to spare. Here's a few pics of the casework:

rear panel, .125" thick... the IEC cutout was slow going:


top plate drilling, w/transformer:


detail; got to love a stepped bit:


board mounted under top plate:


Last night I finished the wiring, and plugged it into the variac... ready for smoke! Ah, but no smoke or sparks. Everything seemed to be running as it should. Checked the plate voltage and power supply, they are a little on the low side throughout. I connected the PSU using the 120v leads first (for preliminary testing), and will swap them to the 110v leads tonight and recheck voltage readings. The stage is tube rectified with a 5Y3. So, I'm also on the lookout for a reasonable 5Y3 with an ST envelope.
Maybe I will get a listen this weekend.
post #2 of 32
Quote:
Last night I finished the wiring, and plugged it into the variac... ready for smoke!
You did not let the magic smoke out of the box ?

So it,it is still inside waiting ?


uh ohhh

So on to the chassis plate :

All holes including the IEC and tube socket cutouts were done by hand ? If yes then pat yourself on the back man.Very professional looking job

and obviously,we need the dirty little details on how this baby sounds
post #3 of 32
Other than a Dremel w/ cutting disc (or a CNC machine!!), what is the easiest way to cut the square IEC connector hole ?!?
post #4 of 32
Quote:
what is the easiest way to cut the square IEC connector hole ?!?
A scroll saw.
post #5 of 32
Thread Starter 
Quote:
Originally Posted by rickcr42
You did not let the magic smoke out of the box ?
I ordered some smoking resistors (the Robert Goulet metallized type) from n_maher, but he is out of stock. I think he used them all up in his PPA! (heh).

Quote:
Originally Posted by chillysalsa
Other than a Dremel w/ cutting disc (or a CNC machine!!), what is the easiest way to cut the square IEC connector hole ?!?
I use a shark-guided laser beam most of the time.
But for this project, I used a stepped drill bit, scrollsaw, a hand file, and about 8,000 calories.

For the IEC, I drilled a .75" hole, then used a scrollsaw to cut out to and along the line I scribed. You can also use a small jeweller's saw, but either way, you have to go REALLY slow, as the aluminum is soft and there is a lot of drag. Ease it along. Took maybe five minutes with the saw. This sounds fast, but when you are proceeding at a snail's pace, it feels and sounds like forever. Then I file the last 64th" or so out to the line... another 15 minutes, or more, depending how you make out sawing. I do have a couple Dremel tools, but I've never had very good luck cutting an IEC opening with them.

The first three (smaller) tube socket holes were drilled with a single stepped bit. The third (rectifier) hole was beyond the reach of my drill press! And although I have maybe four Greenlee punches, I don't have one that fat. I was about to panic, but figured I would try the Makita cordless drill with the mongo stepped bit. This bit is intimidating in the press, so it did not look promising. Well, if you don't have a giant stepped bit, buy one now. This thing even works with a hand-guided rechargeable drill. I applied some kerosene to the bit first, and the plate was screwed to a scrap of plywood, then I used a 5 gallon pail for the support. Took 2 minutes total, stopping to clean away the swarf now and then.

When I cut normal IEC openings, the "D" shaped type, I will usually lay out the barn-shape of it with a little template, then drill out the six corners with a 3/16" bit. Then connect the dots with a saw, and file. It's slow, but it comes out nice and neat. When I was building amps regularly, I'd have paid out for a nice IEC punch, but never found one that was a normal draw-stud type.
post #6 of 32
Even better Mark.Very nice work man and I am totally 100% impressed with how you go about constructing your projects, as always
post #7 of 32
Thread Starter 
Thanks man.

I left out one KEY detail. When you are cutting big holes with any spinning tool, you really need to cover the material with either a layer of heavy masking tape, or some contact paper (plastic actually). Otherwise, you will find that suddenly a long strand of material will start swinging around and make a nice rosette pattern around the hole, possibly slicing your finger open, too. The masking tape actually works better for me, I find that the bit will tear through it, while palstic film sometimes pulls away, letting bits of swarf underneath.

The stepped bit did not really do this, but many ordinary jobber bits- the type most people have on hand, do just that. It's a good way to ruin your day, and your panel.
post #8 of 32
Holy smokes batman.... they want $9,959.00 for a completed Cornet2?

What parts came in the kit Mark?
post #9 of 32
Thread Starter 
Quote:
Originally Posted by MisterX
Holy smokes batman.... they want $9,959.00 for a completed Cornet2?

What parts came in the kit Mark?
What was that thread about 'does DIY save money?'
I guess NOT!

I think it's $999 for a built one. You can build it yourself with the parts he describes, for about $380, or $300 without the chassis, if you already have something suitable.

The "1/2 kit" is more like a "1/4 kit", in that it is the PC board, a little manual describing the parts selection, schematic, and a layout diagram for the four tube holes in the cover plate. Which is nice, since you want them to line up to the sockets below, hopefully.

I was sweating that last detail, but it lines up just fine.
post #10 of 32
Yeah, I was always drilling the corners of the IEC, and then doing the connect the dot thing with a dremel cutting disk... of course every now and then the dremel would 'bite' too much and screw you, so I would cut from the interior side that won't be visible anyway.

I was kind of hoping there was some magic method.
post #11 of 32
Quote:
Originally Posted by Voodoochile
I ordered some smoking resistors (the Robert Goulet metallized type) from n_maher, but he is out of stock. I think he used them all up in his PPA! (heh).
Oh man... just like that my head-fi legacy has been cemented.

I was about to say, "Nice work Mark, very clean panel layouts and holes. That IEC cutout is a thing of beauty. Let us know how it sounds, blah blah blah." What I would say now is not suitable for Head-Fi .

Nate

P.s.
post #12 of 32
Quote:
Originally Posted by Voodoochile
I ordered some smoking resistors (the Robert Goulet metallized type) from n_maher, but he is out of stock. I think he used them all up in his PPA! (heh).
In Nate's defense, it was my PPA that had the smoking resistors, and it was my attempt at adjusting the buffer bias that did said resistors in, so let's not let Nate's legacy be tarnished as a result of him helping me with my screw-up!!!

That said, beautiful work!
post #13 of 32
Quote:
Oh man... just like that my head-fi legacy has been cemented.
I smell a custom title coming
post #14 of 32
Quote:
Originally Posted by rickcr42
I smell a custom title coming
Well, as long as you don't smell smoke...


/U.
post #15 of 32
Quote:
Originally Posted by rickcr42
I smell a custom title coming
Bring it on, I ain't skeered. Plus, it could be worse, I could be Oski the Maunshter!

Nate
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