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Thread: The Build: Chassis fabrication to power-on

  1. #36
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    I used to make clocks and misplaced holes in plates are not uncommon. The rule is never to scrap off the plate. Here's a simple technique that works with most metals;

    1. Lightly countersink each side of the hole - I use a hand countersink
    2. Select a piece of rod of the same (or similar) material to the parent. It needs to be a good, preferably tight fit.
    3. Cut it so that it projects 1/2 the diameter on each side.
    4. Rivet over, working from each side.
    5. Cut a small hole in a piece of acetate film and locate this over the rivet 'head'.
    6. Use a riffler or preferably a bulls-foot file to remove the surplus rivet material - the acetate prevents damage to the surrounding metal.
    7. Finish smooth with abrasive papers, making sure the grain and surface texture matches the parent.

    Sounds involved, but takes just a few minutes to do. The rivet swells into a barrel shape and along with the countersinking locks it in place. This technique is centuries old. I was explaining it to a customer about two weeks ago and showed him a clock I'd made with incorrect hole spacing for some wheels, except neither of us could see where the holes had been plugged.

    Practice on some scrap to get the feel.

  2. #37
    Senior Member SoulFetish's Avatar
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    Quote Originally Posted by Mick Bailey View Post
    I used to make clocks and misplaced holes in plates are not uncommon. The rule is never to scrap off the plate. Here's a simple technique that works with most metals;

    1. Lightly countersink each side of the hole - I use a hand countersink
    2. Select a piece of rod of the same (or similar) material to the parent. It needs to be a good, preferably tight fit.
    3. Cut it so that it projects 1/2 the diameter on each side.
    4. Rivet over, working from each side.
    5. Cut a small hole in a piece of acetate film and locate this over the rivet 'head'.
    6. Use a riffler or preferably a bulls-foot file to remove the surplus rivet material - the acetate prevents damage to the surrounding metal.
    7. Finish smooth with abrasive papers, making sure the grain and surface texture matches the parent.

    Sounds involved, but takes just a few minutes to do. The rivet swells into a barrel shape and along with the countersinking locks it in place. This technique is centuries old. I was explaining it to a customer about two weeks ago and showed him a clock I'd made with incorrect hole spacing for some wheels, except neither of us could see where the holes had been plugged.

    Practice on some scrap to get the feel.
    DAMNIT, MICK! I would LOVE this if it was a forum option! This sounds like a great technique and I have some really nice hand counter-sink/deburring tools, so it should be easy-peasy with aluminum.

    Gingertube, I dig the idea of perforating the aluminum as well, but, I'm trying to find ways of cutting down on the build time.
    Hello, my name is Corey, and I'm a recovering shredder. I has been 2 months since my last sweep arpeggio.

    I'm probably being a smart ass..

  3. #38
    Senior Member SoulFetish's Avatar
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    So I've pretty much set up the wiring for the back panel (bias controls & test points, driver and bias protection etc.).



    The few odds and ends I'm missing are a .77uF-.82uF axial cap, and a 6-32 nylock nut... I think that's it. Oh, and some small heat shrink tubing.
    What are your opinions on grid protection, should I use a couple of NE-2 lamps or zeners? I have a bin of 45V/5W zeners, but the leads are too big. So, I'll have to get some smaller ones if I decide to go with the zener diodes.
    mikepukmel likes this.
    Hello, my name is Corey, and I'm a recovering shredder. I has been 2 months since my last sweep arpeggio.

    I'm probably being a smart ass..

  4. #39
    Old Timer Tom Phillips's Avatar
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    Quote Originally Posted by SoulFetish View Post
    Ö the other thing is when my soldering iron chord gets caught on something or when it (or other leads) gets in the way on my bench. I want to share a cheap, easy, quick trick to keep your cable up and out of the way. If you have a pegboard, go to a Staples (or whatever) and get one of those retractable cheap name tag/card holder things ...You can hang it from a long pegboard hook and use this to keep the chord out of the way and has a decent range to act as a runner....Problem solved...
    What a great idea! Iíve been racking my brain to devise a way of keeping the soldering iron cord from hanging over the edge of the bench and getting caught in the top drawer. I think a good place to hang it is right under the test equipment shelf over my bench.
    Thanks,
    Tom
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  5. #40
    Senior Member Enzo's Avatar
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    Take a tip from mom. ANy number of folks make steam iron cord holders, places like Bed Bath and Beyond sell them

    laurastar-cable-holder-steam-109-209x295.png

    It is a springy thing that clamps to the ironing board - or work bench - and holds the cord up.
    Jazz P Bass and SoulFetish like this.
    Education is what you're left with after you have forgotten what you have learned.

  6. #41
    g1
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    Your solder irons ran on steam back in the day?


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    Quote Originally Posted by Justin Thomas View Post
    In my ideal world, I'm not too loud - your room is too small!

  7. #42
    Senior Member Enzo's Avatar
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    You bet, and they didn't burn just ANY coal, it had to be anthracite.

    My mom's iron ran on steam.
    Education is what you're left with after you have forgotten what you have learned.

  8. #43
    Senior Member SoulFetish's Avatar
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    Quote Originally Posted by Enzo View Post
    Take a tip from mom. ANy number of folks make steam iron cord holders, places like Bed Bath and Beyond sell them

    Click image for larger version. 

Name:	laurastar-cable-holder-steam-109-209x295.png 
Views:	17 
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ID:	43349

    It is a springy thing that clamps to the ironing board - or work bench - and holds the cord up.
    I've noticed that some of the high end soldering stations are actually equipped with cable management. I was checking out some JBC stations, but I had to stop. I was getting tool envy, and a $600+ New soldering iron is way down on my list of necessities right now.( unfortunately). First things first. I need to get a more practical scope than this:

    Hello, my name is Corey, and I'm a recovering shredder. I has been 2 months since my last sweep arpeggio.

    I'm probably being a smart ass..

  9. #44
    Senior Member SoulFetish's Avatar
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    DONE!!!
    Made all the wiring connections - jacks, pots, tube sockets, switches, etc.
    (I still need a friggin' .82uF cap, but I can move on without it for now)



    So, after I put some of the components back on the board, I think I'm ready to fire it up for the first time. (finally!)
    I'm nervous. I don't want to get ahead of myself and forget something stupid, like, connecting it to a load. Or, forgetting to put in a mains fuse and wondering why it wont turn on. Guys, I need some of your ol' bastard wisdom here. talk me through it.
    Wait.... I still need to put in the grid protection. So, no opinions on whether to use neon lamps or zeners, huh?
    catalin gramada likes this.
    Hello, my name is Corey, and I'm a recovering shredder. I has been 2 months since my last sweep arpeggio.

    I'm probably being a smart ass..

  10. #45
    Old Timer Leo_Gnardo's Avatar
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    Quote Originally Posted by SoulFetish View Post
    I still need a friggin' .82uF cap
    It is an odd value, can't you use a 1 uF or .68?

    I still need to put in the grid protection. So, no opinions on whether to use neon lamps or zeners, huh?
    Can't say I've ever seen an audio amp that had grid protection, just stopper resistors. Maybe radio transmitters? Modulator amps? I wouldn't worry about it. Slap in a 1 uF until you run across a .82 (or parallel .68 with .15 if the value is that sensitive.) Plug in your speaker or load resistor, dial your creation up slowly on the variac while monitoring voltages & let's find out how it sounds. Great looking build!

  11. #46
    Senior Member SoulFetish's Avatar
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    Quote Originally Posted by Leo_Gnardo View Post
    It is an odd value, can't you use a 1 uF or .68?



    Can't say I've ever seen an audio amp that had grid protection, just stopper resistors. Maybe radio transmitters? Modulator amps? I wouldn't worry about it. Slap in a 1 uF until you run across a .82 (or parallel .68 with .15 if the value is that sensitive.) Plug in your speaker or load resistor, dial your creation up slowly on the variac while monitoring voltages & let's find out how it sounds. Great looking build!
    It is odd but, that value was set after dialing it in by ear. I could get away with a .68uF drifting on the high side of it's tolerance. I'll try some others again and see if it's much a' do about nothing.
    The grid protections is to keep the EL84 grids from dropping to -150V until the tubes start conducting.
    Hello, my name is Corey, and I'm a recovering shredder. I has been 2 months since my last sweep arpeggio.

    I'm probably being a smart ass..

  12. #47
    Senior Member Enzo's Avatar
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    Wouldn't -150v on the power tube grids simply put the tube in cutoff so no current would flow? And why would that be a problem?
    Education is what you're left with after you have forgotten what you have learned.

  13. #48
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    .33 & .47 in parallel should get you very close to your .82
    Then you can make up some myth about why you must use those 2 in parallel in that particular spot for mojo.
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    Quote Originally Posted by Justin Thomas View Post
    In my ideal world, I'm not too loud - your room is too small!

  14. #49
    Senior Member SoulFetish's Avatar
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    Quote Originally Posted by Enzo View Post
    Wouldn't -150v on the power tube grids simply put the tube in cutoff so no current would flow? And why would that be a problem?
    I'm just trying to avoid exceeding the max grid to cathode voltage of 100V as specified by the datasheet.
    g1 likes this.
    Hello, my name is Corey, and I'm a recovering shredder. I has been 2 months since my last sweep arpeggio.

    I'm probably being a smart ass..

  15. #50
    Senior Member SoulFetish's Avatar
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    Quote Originally Posted by g1 View Post
    .33 & .47 in parallel should get you very close to your .82
    Then you can make up some myth about why you must use those 2 in parallel in that particular spot for mojo.
    Thats pretty much what I did to come up with the ".77uF" when I was voicing the circuit.
    The reason I wanted to avoid parallel-ing two caps, was space constraints(is what I would say on the record). But man to man... I just don't like the way it looks.
    Hello, my name is Corey, and I'm a recovering shredder. I has been 2 months since my last sweep arpeggio.

    I'm probably being a smart ass..

  16. #51
    g1
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    I'd have never guessed that, the way you threw that wiring together.
    Thus the 'mojo' story.
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    Quote Originally Posted by Justin Thomas View Post
    In my ideal world, I'm not too loud - your room is too small!

  17. #52
    Senior Member SoulFetish's Avatar
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    Quote Originally Posted by g1 View Post
    I'd have never guessed that, the way you threw that wiring together.
    Thus the 'mojo' story.
    I actually found some .75uF & .82uF axials for a song, on good 'ol Electronic Goldmine. I actually allow them to Spam me daily so I can wade through pages of useless parts until that one day they have that treasure you been looking for dirt cheap.

    Not to worry though I'm sure we can find something else in the amp to attach some "mojo" lore to .
    g1 and mikepukmel like this.
    Hello, my name is Corey, and I'm a recovering shredder. I has been 2 months since my last sweep arpeggio.

    I'm probably being a smart ass..

  18. #53
    Senior Member SoulFetish's Avatar
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    Well, after the overwhelming response on whether to use zeners or neon to clamp the voltage at the grids... you guys sure had some hot takes on that one
    (I think we can safely file that one away in the "who gives a sh*t" folder)
    I went with the venerable NE2 lamps, because that's the part I had on hand.




    Oh, and I never got around to ranting about these teflon composite tube sockets. I thought I would give them a try (they weren't cheap either.)
    But have a look at the shit swagging job they did in the center of the tube sockets. That, and they had way too much clearance to move around in the mounting rings.
    I'm not gonna' get into what I did to make that work out, but thumbs down on these. If I use any thermoplastic sockets going forward, I'll use Belton. The difference in quality isn't even close. But I think RG is probably right. Ceramics, while not exotic, may be the best way to go.

    So, that's the last little bit of soldering. Also, I don't have a variac to ramp up the voltage during power on. Would you think that it is a necessity? I have a incandescent limiter ready to go, however.
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    Hello, my name is Corey, and I'm a recovering shredder. I has been 2 months since my last sweep arpeggio.

    I'm probably being a smart ass..

  19. #54
    Senior Member Enzo's Avatar
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    Did you look up the firing voltage of the NE2? I seem to recall it was like 90v. But once it ionizes, it drops to 60v or so. So the voltage across has to drop to that before it extinguishes.
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  20. #55
    Senior Member SoulFetish's Avatar
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    Quote Originally Posted by Enzo View Post
    Did you look up the firing voltage of the NE2? I seem to recall it was like 90v. But once it ionizes, it drops to 60v or so. So the voltage across has to drop to that before it extinguishes.
    Yeah, I checked it out. You're right, but that won't be a problem once the driver starts drawing current the voltage will quickly rise to the bias voltage that's been set. The neon will flash over, turning on only while the cathodes are cold.
    Hello, my name is Corey, and I'm a recovering shredder. I has been 2 months since my last sweep arpeggio.

    I'm probably being a smart ass..

  21. #56
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    What kind of resistors are you using?

  22. #57
    Senior Member SoulFetish's Avatar
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    Quote Originally Posted by mikepukmel View Post
    What kind of resistors are you using?
    Carbon Film, Metal Oxide, and some metal film and wirewound in a few places.
    Hello, my name is Corey, and I'm a recovering shredder. I has been 2 months since my last sweep arpeggio.

    I'm probably being a smart ass..

  23. #58
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    Quote Originally Posted by SoulFetish View Post
    Carbon Film, Metal Oxide, and some metal film and wirewound in a few places.
    Did you missed some types?

  24. #59
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    What limits the current through the neons?

  25. #60
    Senior Member Enzo's Avatar
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    Can the grid circuit p[rovide enough current to threaten the neon lamp?
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    Education is what you're left with after you have forgotten what you have learned.

  26. #61
    Senior Member SoulFetish's Avatar
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    Quote Originally Posted by Mick Bailey View Post
    What limits the current through the neons?
    Load resistors in the driving stage.
    Normally, you see a value of around 100K current limiters for coditions where they will stay on for extended periods. I didn't add any additional resistance to the driver load resistors, because that Won't be conditions here.
    mikepukmel likes this.
    Hello, my name is Corey, and I'm a recovering shredder. I has been 2 months since my last sweep arpeggio.

    I'm probably being a smart ass..

  27. #62
    Senior Member SoulFetish's Avatar
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    I should add that, in it's current configuration, the grid stoppers in addition to the load resistors will limit the current. But, those are subject to change if I decide to drive the grids into positive voltage.
    mikepukmel likes this.
    Hello, my name is Corey, and I'm a recovering shredder. I has been 2 months since my last sweep arpeggio.

    I'm probably being a smart ass..

  28. #63
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    Quote Originally Posted by Enzo View Post
    Can the grid circuit p[rovide enough current to threaten the neon lamp?
    Probably not under normal conditions. I originally had neons in an 807 hi-fi amp I built and on first turn on they would sometimes permanently glow brightly unless the amp was turned off and on again. The glass soon had the shadow you get with a tired neon. I never really investigated it - could have been some kind of oscillation. I originally debated whether to use them, but I clipped them out and the amp has worked fine for years.

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