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Thread: The Build: Chassis fabrication to power-on

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    Senior Member SoulFetish's Avatar
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    The Build: Chassis fabrication to power-on

    This picks up on a conversation which started in Uneumann's thread "Help with chassis" found here:

    help with chassis

    I wanted to post some of the updates as I progress through a build and share some of the things I've learned (and am learning) -– what has paid off and things I would do differently. I had posted some images I'd taken of different stages of the chassis and left off talking about the different techniques for cutting the square hole needed for an IEC. I came up with a way of creating the mounting hole using a drill and file which worked out way quicker than I had anticipated. This works very well for those who don't have access to a punch or mill. This is the result:

    iec-jack-mounting-holes.jpg

    To Keep the chassis clean and simplify the physical layout, I opted to use some insulated turret terminals with a threaded base. This required tapping some holes in the chassis. With the proper tools (and a little patience to make sure to locate them and wait for them), this ended up being a painless task.
    Here are a couple of pictures of the terminals and tapping 2-56 threads:

    tapping-aluminum-threaded-terminals.jpg
    -
    tapping-aluminum-threaded-terminals2.jpg

    Up to this point the all of the holes were falling withing really close tolerances to the drawing I had created. All of the planning was really paying off... until I got impatient. I made a DUMB-ass mistake.
    I'm have to work in the morning, so I'm crashing. But, I'll tell you about it later and ask for some advice on the best way to deal with it.
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    There are three important information missing here:
    - where did you buy insulated turret terminals with a threaded base?
    - what was the DUMB-ass mistake (we all want to learn)?
    - why didn't you use such terminals?
    terminal.jpg
    They would make your life much easier.

    Mark

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    Senior Member SoulFetish's Avatar
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    Quote Originally Posted by MarkusBass View Post
    There are three important information missing here:
    - where did you buy insulated turret terminals with a threaded base?
    - what was the DUMB-ass mistake (we all want to learn)?
    - why didn't you use such terminals?
    Click image for larger version. 

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    They would make your life much easier.

    Mark
    Mark, those are 3 great questions! I'll answer them in the order you asked them:
    1. I have two different types, but I think I scored those on eBay. I have some others that are swage mount which I am thinking of selling as it is easier for me to tap the chassis, rather than swage mount them. I don't have the tooling to properly press fit them. Unfortunately, eBay is probably the best way to acquire them as buying them through a distributor is prohibitively expensive in my experience.

    2. The mistake: I was getting frustrated that progress was going slower than I had hoped. I made the decision to use M3 fasteners over 4-40, or 5-40 because I think it is a superior thread for small fasteners. This can be a challenge because here in the States, the standard is.... well.., Standard (or Imperial), and M3 is Metric. In any case, clearance holes for an M3 fastener range from around 3.2mm(close fit) - 3.6mm(free fit). I had opted to look for a 3.3mm-3.5mm stub drill made of TiN (Titanium Nitride) coated HSS (High Speed Steel). This material was chosen for drilling aluminum for a few reasons, but I'll indulge anyone who wants to know why later in an effort to shorten the answer. I knew it was going to be another several days until the drill was going to arrive, and I already cleaned the shop (twice). I was getting impatient one night and I though "I have an 1/8 inch drill I can use. It's a tight fit, but I can make it work". So I said "f_ck it" and decided to make some holes. While marking the chassis for the board standoffs, I marked a standoff hole that wasn't supposed to be there (it was to feed some wires through the board). I only caught the mistake after I drilled the hole. So, now there is an 1/8th inch hole in my chassis which isn't supposed to be there, and it REALLY burns my ass. The problem wasn't that I used an 1/8th inch drill, the problem was my state of mind and the motivations behind my decision making which made it much more likely for mistakes like this to happen. It would have been wise to wait for the tools and materials which were chosen for thoughtful reasons, over making impatient decisions trying to "get away with it".

    3. I could go with "easier" and use those types of terminals. But, I think for this application the terminals I chose are more mechanically rugged, make much more efficient use of space, are marginally more difficult to install, and present a more elegant appearance. I've used that style terminal before and if I needed to make several electrical connections in the area, I probably would opt for something like that.

    Oh, so does anyone have any suggestions on how to fix or plug the 1/8" hole in my aluminum chassis??
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    Supporting Member mozz's Avatar
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    Rivet.
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    Senior Member SoulFetish's Avatar
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    Quote Originally Posted by mozz View Post
    Rivet.
    Moz, you suggestion sounded good at the time... But, now it looks weird with a rivet sticking out of the outside of my chassis.
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    Supporting Member The Dude's Avatar
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    It wouldn't bother me, but I understand OCD. If it really bothers you, you could have it welded closed and file/sand/polish it back smooth. A lot of work for a tiny hole. I don't think they make an 1/8" box fan.
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    Senior Member SoulFetish's Avatar
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    no, the rivet was a great idea! It's not really sticking out of the chassis (I'm not that soft). It's flush against the outside and hidden inside under the turret board inside.
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    Senior Member SoulFetish's Avatar
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    Quote Originally Posted by The Dude View Post
    If it really bothers you, you could have it welded closed and file/sand/polish it back smooth. A lot of work for a tiny hole.
    I'm not going to lie, that thought crossed my mind.

    I had done all the other chassis work except for the standoff holes, and after I realized I screwed up, I considered scrapping the chassis and starting again. But, I backed away from the ledge when I realized that's the kind of crazy which compels someone to build a plateau sculpture out of mashed potatoes and heading for the hillside.
    I was pretty sure I'd bounce back just fine.
    But, Moz, your friggin' rivet solution... so simple, yet so brilliant.
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    Supporting Member mozz's Avatar
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    Well i'm glad it was tried. They make a aluminum rod that you melt with a propane torch, have never used them myself though.

    How about a bias test point?

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    Senior Member SoulFetish's Avatar
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    Quote Originally Posted by mozz View Post
    Well i'm glad it was tried. They make a aluminum rod that you melt with a propane torch, have never used them myself though.

    How about a bias test point?
    Moz, I think the rivet idea was the winner. Plus, it was better than a "dummy" screw idea which i thought of doing as a last resort.

    I'm getting ready to mount the transformers and some of the hardware, and start the wiring. The first connection I'll make is the earth bond. Then I was going to wire the heaters and mains connections. Any advice? Something I may not catch and is easy to miss?
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    Senior Member SoulFetish's Avatar
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    Quote Originally Posted by mozz View Post
    How about a bias test point?
    Oh, my bias points will already be here:


    img_2282.jpg

    img_2283.jpg
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    Supporting Member mozz's Avatar
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    How about one of these?
    resized_20161125_174014.jpg

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    Senior Member Enzo's Avatar
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    Pop rivets have the hole, but other rivets are solid like the above example. DUmmy screw? If there are no other exposed rivets, but there are other exposed screws, then an extra matching screw head won;t look out of place.

    I have to admit, I have mounted smallish Dale or Arcol aluminum power resistors to chassis before, and went to far as to make a template for the hole spacing. They have opposite corner mounting holes. Like pins 1 and 5 on a DIP8. Sure enough, after drilling my carefully spaced holes, I found out I needed to invert the pattern
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    Senior Member SoulFetish's Avatar
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    Quote Originally Posted by Enzo View Post
    I have to admit, I have mounted smallish Dale or Arcol aluminum power resistors to chassis before, and went to far as to make a template for the hole spacing. They have opposite corner mounting holes. Like pins 1 and 5 on a DIP8. Sure enough, after drilling my carefully spaced holes, I found out I needed to invert the pattern
    Enzo, I hear you. I have a graveyard of Hammond aluminum which serves as a memorial to those moments when I realized I drilled the wrong @#*!-ing hole(s).
    But it was supposed to be different this time.. I even made sure to label my templates as "inside view" and "outside view" (I'd have been screwed if I didn't do that).

    template.jpg

    But I'm going to cut myself a little slack on the errant drill hole. I've been reading Bob Pease's book "Troubleshooting Analog Circuits" (great suggestion by the way), and from the very beginning he champions the wisdom of creating space in the building(testing) phase for changes which will need to be made due to issues which present themselves in "real world" application.

    Here is a practical example of a couple of issues I ran into during the actual building phase:
    Taking the time to score, center-punch, and drill pilot holes was making for quick and precise fabrication of the chassis. Initially, everything was going according to how I planned it and had drawn it out. (...Other than drilling an errant mounting hole which has been discussed ad-nauseam above I'm sure)
    The first amp I built, I did from the ground up(which was the last amp I built) and essentially improvised the entire build. The amp went through so many iterations and rebuilds that the chassis now looks like it was dragged through the Normandy invasion. One of the areas I remember running into difficulty was lining up the mounting holes for the tube sockets. I though I would solve that problem this time by keeping to tight tolerances by precisely marking the center points, and drilling pilot holes. Here is the result.
    scoring-marks.jpg
    center_punching_score_mark.jpg
    results.jpg
    tube-socket-pilot-holes.jpg

    Not too bad, I though. However, in actuality, doing the preparation like this (in the order in which I did it), proved to complicate the actual fabrication and make for more work in post production in ways I hadn't anticipated. I'll tell you about it in the next post because I think I'm going to run out of attachments in this one. To be continued....
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    Senior Member SoulFetish's Avatar
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    Shop maintenance and re-tooling

    I've been meaning to circle back here and update some of my progress.
    So much of the construction phase of this project has been research, parts procurement, waiting for materials, and acquiring the tooling I need to do the kind of work I set out to do. The right tools are clutch! What ever tools I've needed, I've tried to get the best quality tools I can afford. I have to be thrifty and resourceful with this because I have limited resources for the most part. If the tools I need aren't readily available or out of my budget, I try and come up with a way to build or make what ever I need. Here is an example:
    I needed a drill press. There are many drill presses I would LOVE to get my hands on and use. But I needed something to start this amp and I found someone selling a Delta 11-980 for $65. This is about as base model as you can get. But, I bought it, did the chassis work with it, and realized that the chuck was in rough shape.
    So, while I was waiting for some drills to come in and some other parts, I found an old Jacobs chuck with the same taper mount as my drill press. So I rebuild the Jacobs chuck and cleaned it up. Once the chuck was off, I couldn't help it and took the entire drill press apart and cleaned and rebuilt that. After reassembly, I set up a dial indicator to check the chuck and spindle alignment and it showed .003" of runout. That's pretty good for this machine.

    I was up and running and ready to make the turret board. I wanted to make a good quality anvil to set the turrets into the board, so I made a 1/4" stainless steel anvil. It just so happened that I had so old RV4 pots with the long shafts which I wasn't going to use so I cut the shaft off to use for the anvil. After a couple of failed guesses at how to drill this out, I found a great technique for drilling a dead center hole in a small diameter rod. (I'll tell anyone who's interested, but it makes this a longer story). Anyways, Here are some pictures of the anvil and board assembly:

    diy-stainless-steel-turret-swaging-anvil.jpg

    turret-swaging-horizontal-plane.jpg

    Dude, I was psyched. This thing lined up dead nuts.

    turret-swaging-tool-alignment.jpg

    progress-halfway-through.jpg
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    Senior Member SoulFetish's Avatar
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    What a great feeling it is to have a soldering iron in hands, to make me feel like I'm actually doing amp work. I had to wait til today because I wasn't even CLOSE guessing how many turrets I would need and had to wait to get more from Allied. Apparently, I didn't want to count?
    Anyway, just getting the soldering underway and it feels good; power supply is coming along


    board-caps.jpg
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    Senior Member SoulFetish's Avatar
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    update :)

    Can I just say +1 for printed circuit boards

    I just finished up all the "on board" wiring connections:

    boardwork-empire.jpg
    boardwork-empire-2.jpg

    It's important but... a little tedious doing this part. I think I'm really liking the idea of a hybrid pcb/handwired approach. That would have made for much quicker work.
    I guess I'm a fan of hybrid techniques, because I thought of a way to make quick component changes when I go live and start testing this amp. This amp's is new and if I need to make changes (which I'm sure there will be a few) because real world results may differ from what I expected, I wanted to be able to make the changes efficiently. So, I "socket-ed" the turret terminals holding the components most likely to be altered or tweaked to get the results I'm after. I soldered some beryllium copper/brass sockets which sit nicely in the turrets to allow me to experiment and breadboard if I need to.

    turret-sockets.jpg

    It's a little more work on the front end, but it should really give me some flexibility and save me time if I need to change things. I like to think Bob Pease would be pleased with my contingency plan

    One last thought. There are two things that frustrate me when I'm on the bench working. The first– not being able to find a tool which I literally just put down, I haven't gone anywhere to have left it, and it may as well vanished for at least until I don't need it any longer. I mean, it has to be in a (generous) 5' radius, doesn't it? Logically? Nope. It's f*cking GONE. That ever happen to you guys?
    I haven't solved that problem yet, but 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 -
    like this:
    z0u89vpcpex_.jpg

    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.
    Like this:
    soldering-iron-chord-trick.jpg
    Problem solved.
    Anyway, that's it for tonight. Keep it real
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    Senior Member SoulFetish's Avatar
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    Heater wiring.

    heater-wiring-2.jpg
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    Senior Member SoulFetish's Avatar
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    After giving up my week and a half long quest to find some great deal or inexpensive cache of RV4 pots in the values I needed (of course, all the same type), I gave up. It was ambitious, I know, but I guess I'm just cheap. So, I bit the bullet and faced up to the fact that I was going to have to pay retail. What the hell, I can't win 'em all. So my pots arrived and I was glad to be back at it!. It was time to wire up some of the front panel.





    You may have noticed the empty hole between the last to pots to the right. It's for a common, inexpensive, simple 2PDT toggle switch, which for some crazy reason I didn't have, and thought would just end up showing up? (I can't believe I didn't have one!).
    It's funny, so far it's has been the little odds and ends that have been the hair across the ass of this build. A resistor value that I was sure to include in an order, or a small fastener, or common small type of switch that I can't believe I didn't have. This is often what has brought progress to a grinding halt. Okay, that's a little hyperbole, but they're important parts of this that I'm relying on. Whenever I try to take a short cut around it, I usually end up regretting it.
    I'm really beginning to see the value in a complete BOM, and inventory check list.
    But, what I do have is geeks for friends. So I put out the Bat Symbol, and my buddy Scott sent me this and said "are these what you're looking for?"







    (Damn right these are what I'm looking for).
    Before too long I was making it rain mini 2PDT in my shop again. I finally got to put the board in and began lining up and cutting the leads to size. I'm starting to get psyched. Check it out, almost looks like an Amp
    Finally!! I'm hitting the home stretch!
    .



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  20. #20
    Supporting Member mozz's Avatar
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    In 100 years, that amp will still be around. Looks very nice. The pots look like the old Allen Bradley type J. What are those caps? Vishay?
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    Senior Member SoulFetish's Avatar
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    Quote Originally Posted by mozz View Post
    In 100 years, that amp will still be around. Looks very nice. The pots look like the old Allen Bradley type J. What are those caps? Vishay?
    Yes Sir, MKP1848 series. Thanks for the kind words.
    I have some parts comkng today, and Thats the last batch. I think I may be ready to fire it up by the end of the week. Im exited to put it under test and hear this thing. Hey, Ill finally get to play some guitar for a change! Wont that be something
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    Quote Originally Posted by SoulFetish View Post
    After giving up my week and a half long quest to find some great deal or inexpensive cache of RV4 pots in the values I needed (of course, all the same type), I gave up. It was ambitious, I know, but I guess I'm just cheap. So, I bit the bullet and faced up to the fact that I was going to have to pay retail. What the hell, I can't win 'em all. So my pots arrived and I was glad to be back at it!. It was time to wire up some of the front panel.

    ......

    You may have noticed the empty hole between the last to pots to the right. It's for a common, inexpensive, simple 2PDT toggle switch, which for some crazy reason I didn't have, and thought would just end up showing up? (I can't believe I didn't have one!).
    It's funny, so far it's has been the little odds and ends that have been the hair across the ass of this build. A resistor value that I was sure to include in an order, or a small fastener, or common small type of switch that I can't believe I didn't have. This is often what has brought progress to a grinding halt. Okay, that's a little hyperbole, but they're important parts of this that I'm relying on. Whenever I try to take a short cut around it, I usually end up regretting it.
    I'm really beginning to see the value in a complete BOM, and inventory check list.
    But, what I do have is geeks for friends. So I put out the Bat Symbol, and my buddy Scott sent me this and said "are these what you're looking for?"

    ......




    (Damn right these are what I'm looking for).
    Before too long I was making it rain mini 2PDT in my shop again. I finally got to put the board in and began lining up and cutting the leads to size. I'm starting to get psyched. Check it out, almost looks like an Amp
    Finally!! I'm hitting the home stretch!
    .
    Your build quality is a work of art!
    Last edited by mikepukmel; 04-17-2017 at 07:18 PM.
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    Quote Originally Posted by SoulFetish View Post
    Heater wiring.
    Again, beautiful job. It looks like solid core, what gauge are you using, is it 18ga?

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    Hi soulfetish, great build I agree. Inspires me to make a very neat build. Great j0b
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    Senior Member SoulFetish's Avatar
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    Quote Originally Posted by mikepukmel View Post
    Again, beautiful job. It looks like solid core, what gauge are you using, is it 18ga?
    It is solid core wire. It's 20AWG/600V wire code UL1015. I also use type MIL-W-76, which is mil spec 1000V wire when I have it. I my opinion, 20AWG seems to be the sweet spot for what we do. 22AWG, is a little to thin and is prone to shifting around, while 18AWG solid core is so stiff when soldered, that if your not careful working with it, you can break some terminals.
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  26. #26
    Supporting Member The Dude's Avatar
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    Very tidy build! I hope it sounds as good as it looks. Thanks for the update shots!
    “Yeah, well, you know, that’s just, like, your opinion, man.”

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    Quote Originally Posted by SoulFetish View Post
    It is solid core wire. It's 20AWG/600V wire code UL1015. I also use type MIL-W-76, which is mil spec 1000V wire when I have it. I my opinion, 20AWG seems to be the sweet spot for what we do. 22AWG, is a little to thin and is prone to shifting around, while 18AWG solid core is so stiff when soldered, that if your not careful working with it, you can break some terminals.
    Thanks!

  28. #28
    Old Timer tedmich's Avatar
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    nice build!

    You might have to clean those fancy PEC pots eventually...

    Randall Aiken has rethought their use:

    "caused me to switch to the hot-molded carbon types from PEC, which I now use exclusively. They are extremely well-built units, even better looking than the Clarostat, but more expensive. These RV4 type pots are more expensive than other types, but their sealed construction, reliability, and precision feel makes them worth the extra cost. UPDATE: I have to admit I was wrong on this issue. After having quite a few amps in the field for going on 12 years now, I am starting to see a few complaints of noisy pots from people who own my amps. Normally, I would just tell them to open the amp up and spray some contact cleaner in the pots. Unfortunately, you can't do this with a sealed pot, so you have no choice but to replace the pot. No pots are going to last forever, so you may as well use a cheaper pot like the Alpha, that can be cleaned or replaced for a fraction of the cost of one PEC pot. The Alphas have a nice smooth torque feel to them."

    from Technical Q&A
    about 10% down the page

    Of course I never actually move my knobs so YMMV

    In general I try to use conductive plastic or cermet pots over anything carbon but I still prefer CHEAP and love the construction of old RV4s
    Last edited by tedmich; 04-18-2017 at 03:11 AM.
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    Senior Member SoulFetish's Avatar
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    I would add that the heater wire is 18AWG stranded which is the thickes diameter that will fit in most 9-pin sockets (barely fits as it is).
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    Quote Originally Posted by SoulFetish View Post
    I would add that the heater wire is 18AWG stranded which is the thickes diameter that will fit in most 9-pin sockets (barely fits as it is).
    Thanks SoulFetish. The last thing Im toiling with on a first amp build is getting the right wire. I read someplace that "you MUST use solid core wire..." on the heaters, but then seems lots of builders use 18ga stranded and I haven't heard of any horrible mushroom could things happening with those amps. (would be nice not to burn up a 200.00 transformer the first time around )

  31. #31
    Senior Member Enzo's Avatar
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    Be VERY wary when people use terms like never and always around some element of the circuit.

    Stranded wire tends to be more springy that solid, solid you can bend to shape and it stays that way. But a million Fender amps were wired with stranded, and it seemed to work out for them, eh?

    The transformer has absolutely zero idea what kind of wire you used to connect it to the rest of the world.
    Education is what you're left with after you have forgotten what you have learned.

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    Senior Member SoulFetish's Avatar
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    I use stranded for the first few tubes because its flexible and its easier to adjust around wires and corners. The last two tube sockets in the chain are solid core.
    If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

  33. #33
    Senior Member Enzo's Avatar
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    I think the important thing is the decision is totally based on practical issues in assembly, not anything electronic.
    SoulFetish likes this.
    Education is what you're left with after you have forgotten what you have learned.

  34. #34
    Senior Member SoulFetish's Avatar
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    Quote Originally Posted by Enzo View Post
    Be VERY wary when people use terms like never and always around some element of the circuit.

    Stranded wire tends to be more springy that solid, solid you can bend to shape and it stays that way. But a million Fender amps were wired with stranded, and it seemed to work out for them, eh?

    The transformer has absolutely zero idea what kind of wire you used to connect it to the rest of the world.
    On that point. If tranformer manufacturers tought you should only use solid core wire on a heater supply, they would use solid core as secondary leads. At 60Hz (or DC), the difference in wire type is almost entirely based on the benifits of it's physical properties, not electrical. I could have done them all in solid or stranded.
    g1 likes this.
    If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

  35. #35
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    To revisit something above.
    What happens when we end up with an unwanted unsightly hole in the chassis.
    Well often you can pull the professional design engineers BS (which I am intimately familiar with having been one for 30 + Years) and you call it a FEATURE.
    Add a heap more holes in the chassis, down each side of the power tranny, around each output tube, and you explain (quite correctly) that it is for thermal management - to keep the heat flows away from critical circuits and aid in cooling.
    Cheers,
    Ian

    P.S. One orphan hole does look crappy but heaps of them can look like (and be) a feature.
    Justin Thomas and SoulFetish like this.

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