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  1. #1
    Les Paul Forum Member reswot's Avatar
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    NAD - the Cosmic Ray

    Hey, all... Just thought I'd share a little amp that I built for my own amusement.

    I had the idea of building an amp with a Komet-style preamp mated to a Princeton Reverb output section so that it wouldn't blow out my windows when I played it. As I was working out the design, though, I decided to beef up the output section by going with heavier-than-stock Deluxe Reverb-style PT & OT, and also adding a choke. I worried that the PR OT couldn't handle what I was going to throw at it. While I was beefing up the trannies, I also increased filtering in the first couple of stages from 20uf to 40uf to tighten it up a bit.

    I used a PR-style chassis from Weber and Heyboer PT and OT. I ordered the choke from Classic Tone. I had the board made by Doug Hoffman. I got the faceplate and rear plate made by Precision Design in IN; they had the dimensions of Weber's chassis, so it was easy to tell them what I wanted.

    For the cab, I got a PR-sized cab from Peter Mather. I wanted to do a little tribute to Komet, so I had him put the white triangle on the top. I went with a Mesa-style handle and no chassis straps because I didn't want to distract too much from the tolex.

    For the speaker, I used a Weber Legacy 65 watt, 75Hz, 50 oz magnet. I could have used a 65 watt H75 from Scumback, or even a Celestion Creamback, but I wanted the frame painted red. I suppose I could have asked Jim if he'd have painted one of his frames red, but I didn't think about it...

    When I was thinking of what to call it, I thought I needed a "space-y" name (y'know, Komet, Asteroid...) and thought of Cosmic Ray's Starlight Cafe at Magic Kingdom. I thought the name "Cosmic Ray" was fitting and kind of funny, so I went with that.

    Anyway, it sounds really cool. I've tried it with both 6V6GTs (from TAD) and a set of 6L6GC-STRs from Tung Sol. Both sound really good. The 6L6s may sound just a bit better, as the midrange is scooped just a bit, but the 6V6s sound good and I don't have to buy another set of tubes (I borrowed the 6L6s from my Vibrolux Reverb). It's really no louder with the 6L6s, as it's going to be limited by the OT. The preamp tubes are all Tung Sols.

    Here are a few pics. I could post the schematic if anyone's interested, but it's not that hard to figure out once you know where I was coming from. I can also post a layout that I made up before built the amp -- a couple of things were moved around when I actually built it, but it's basically accurate.











    Last edited by reswot; 07-31-19 at 04:37 PM.

  2. #2
    Les Paul Forum Member goldtop0's Avatar
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    Re: NAD - the Cosmic Ray

    That's a great build and I bet the tone is superb .......
    Love the '50s look also.

  3. #3

    Re: NAD - the Cosmic Ray

    If it sounds half as good as it looks, you're in business!

  4. #4
    Les Paul Forum Member CoyotesGator's Avatar
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    Re: NAD - the Cosmic Ray

    Nicely done!

    As I see it, I serve the beat. Groove is everything.

    Big Al

  5. #5
    Les Paul Forum Member reswot's Avatar
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    Re: NAD - the Cosmic Ray

    Thanks, guys...

    In hindsight, there are a couple of things I could have done differently.

    If I'd used V2, V3, and V4 positions for my preamp and PI (rather than V1, V2, and V3), I'd have had shorter runs on the leads. I didn't do that, though, because I wanted that extra space to run the leads from the OT without it being to crowded. I thought about both ways, but went with this way. That's one of the problems of using a chassis made for another amp!

    Also, I should have put the hard/soft switch in the third hole, rather than the first. That would have made a much shorter run on these wires. I get a bit of hum in the "soft" position, and I wonder if that's why.

    Other than that it sounds really good. The speaker is still a bit tight, although the folks at Weber did break it in a bit; it'll only get better with more playing.

    The only oddity I've come across is that I cranked the volume full-on yesterday (through an attenuator) and got a thump like a fender vibrato, so I need to sort that out. Still, it was only when it was maxed out and I'd never turn it up that high.

  6. #6
    Les Paul Forum Member
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    Re: NAD - the Cosmic Ray

    Quote Originally Posted by reswot View Post
    I should have put the hard/soft switch in the third hole, rather than the first. That would have made a much shorter run on these wires. I get a bit of hum in the "soft" position, and I wonder if that's why.
    I assume that's the reason for the coiled wire around the switch wire - to try to shield them? I can't see clearly from the photo but it looks as if that is grounded at both ends? If so that could be causing a ground loop, it's normal practice for a shielded wire to ground at one end only. You could try replacing that with some proper shielded wire to see if it helps, also it looks like the switch wires are running pretty much parallel to the heater wires, it might be worth trying to re-route them to keep them away from the heater wiring as much as possible.

    Nice build by the way

  7. #7
    Les Paul Forum Member reswot's Avatar
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    Re: NAD - the Cosmic Ray

    The shield is grounded at only one end; the other end is tucked in the coil. I did it this way because that’s how the Komet is done. I used shielded wire on a previous build.

    I can try rerouting the coil and seeing what happens.

    Thanks.

  8. #8
    Les Paul Forum Member
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    Re: NAD - the Cosmic Ray

    Reshot, that is one sharp looking amp. Thanks for the unveiling, and yes...I would like to see the schematic and layout. I have been looking at and thinking about an Express, and this thread led me to the Francesca schematic, which I had not seen. Again....thanks for showing the beautiful amp and for the gracious offer of a look at your work. I wish. Cold play through ..or even hear it. These types of amps are non-existent around here. I have been considering an Express for some time. This thread might make me come to a decision as to what I want to do with some parts I have.
    "As soon as man does not take his existence for granted, but beholds it as something unfathomably mysterious, thought begins." Albert Schweitzer

  9. #9

    Re: NAD - the Cosmic Ray

    I bet it sounds great.

    What does the hard/soft attack do?

  10. #10
    Les Paul Forum Member reswot's Avatar
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    Re: NAD - the Cosmic Ray

    The attack switch is a connected to a split load plate resistor (or a pair of resistors, actually). It taps off the signal to the coupling cap (or tone stack) either between the two resistors or before (normal) to change the amount of gain.

    Note that I edited this, as last night I was tired and stated it can come after instead of before.

    I’ll try to post the schematic and layout tomorrow.
    Last edited by reswot; 08-03-19 at 08:23 AM.

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