What gets hot besides tubes and transformers?

Discussion in 'Shock Brother's DIY Amps' started by A13X, May 30, 2020.

  1. sds1

    sds1 Tele-Afflicted

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    It's a good point, ignore the Hammond chassis suggestion if this build is say bigger than a 10-15W type build. I did use a .05" for a micro build and it supported the transformers well.
     
  2. jvin248

    jvin248 Poster Extraordinaire

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    .

    Make sure you can create a chimney for cool air to enter at one side and exit hot at the top on the other.

    The ceramic resistors get pretty hot. They often fail due to heat and their solder joints fail due to vibration causing their relatively large mass to wobble back and forth. High heat dissipation needs cause them to be mounted with longer 'legs' so the wobbling problem is worsened.

    .
     
  3. telemnemonics

    telemnemonics Telefied Ad Free Member

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    Extruded aluminum is generally cut with a carbide blade on a woodworking chop saw.
    Milder aluminum can clog jig saw blades before much cutting gets done, but a lot of woodworking tools do work on aluminum.
    All the early Marshall chassis' were fairly thin hand bent aluminum, but over the years the transformers literally crushed the aluminum.
    I had one with the dreaded transformer sag and I made a brace to support that part of the chassis.
    For that matter lots of old Marshalls with steel chassis' display tranformers ripped off their steel mounting tabs, because, Rock I suppose, or roadies. Or just the road.

    On the subject of cutting aluminum with woodworking tools, just today I was cutting some 12' pressure treated 6x6 timber and made an angle cut without sliding the fence off to the side. Cut right through the aluminum. Not the first time.
    Ooops.
     
  4. Lowerleftcoast

    Lowerleftcoast Tele-Afflicted

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    Rob Robinette has an image on his 5F6A mods site which shows the hot bits.
    5F6A Chassis Thermal Image
    https://robrobinette.com/5F6A_Modifications.htm


    I like working with wood as well. IIRC some old radios were just built inside a wood shell. I think you are getting good advice to use some kind of metal chassis or a hybrid wood/metal chassis. I keep thinking of the safety aspect of grounding the power cord.

    Venting the chassis is always a good idea. I don't think a fan is necessary.
     
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  5. Dacious

    Dacious Poster Extraordinaire

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    Resistors get very hot.
     
  6. Engine Swap

    Engine Swap Tele-Meister

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    If the transformers are getting hot, there's a problem with the circuit or the design.
     
  7. tubelectron

    tubelectron Tele-Afflicted

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    @A13X, I did not read the full thread but I will - maybe some of you had already answered in the same way as me, by the way ! ;)

    I often use wood for my Hi-Fi prototypes :

    [​IMG]

    But after that, I shift to aluminium Hammond boxes of the suitable size :

    [​IMG]

    What I like in that formula is that it offers shielding, compactness and a "RetroCool - Laboratory" look... :cool:;)

    That said, most of my friends use wood for the sides and aluminium forn the top with full success.:)

    Yes. I was thinking about the cathode resistor too.

    Sure ! I used it in 1993 on this OTL amp - and I plan to use it on my next OTL release. With a switch, you can lower the speed and make it noiseless if it is a concern : there will be enough air to cool the stuff if you manage adequate vents.

    I have designed :rolleyes: a super-simple trick to allow starting and running of a PC fan at very low (silent) speed. Let me know if you are interested in...;)

    -tbln
     
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  8. Steve 78

    Steve 78 Friend of Leo's

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    Just double check that it is aluminium. For my first and current build I bought a baking pan because it was considerably cheaper than an amp chassis but it turned out to be stainless steel. I'm still using it but it is harder to work with.
     
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  9. Asmith

    Asmith Friend of Leo's

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    You don't need anything heavy duty, a step drill bit that goes up to the size of an octal valve socket and a small file. I've put an amp in a diecast aluminium box using those tools and a 10 watt drill.
     
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  10. sds1

    sds1 Tele-Afflicted

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    Let's just be clear though -- there are no components in a tube amp that get hot enough under non-fault conditions to set a wooden cabinet ablaze. Wouldn't happen.

    I don't that that was ever a legitimate concern.
     
  11. Old Deaf Roadie

    Old Deaf Roadie Tele-Afflicted Silver Supporter

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    Resistors get hot. Once while attending A&P school (aviation maintenance), during the electrical portion our instructor called for 3 random resistor values from the class, and put them together on a breadboard and energizing it. Instructor drones on about Ohm's Law, then goes to grab one of the resistors. His reaction was completely unexpected when he touched one of the energized resistors and you could actually see smoke off his finger. After doing the math, we figured that resistor was dissipating upwards of an entire ampere. Good thing it was only a 24 volt circuit. The students had a good laugh, the instructor not so much.
     
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  12. ricknbaker

    ricknbaker Tele-Afflicted

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    Wooden chassis worked ok for this Marcos

    Marcos_1600_GT.jpg
     
  13. Asmith

    Asmith Friend of Leo's

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    I also wouldn't be worried about the heat either at least from the resistors, most amp chassis have an open side mounted to a slab of wood.

    I would be worried about the valves though, it would depend on the valve. I wouldn't worry about a preamp tube disapting ~2.5W between the plate and heater but something like a 6L6 which disapates 36W would have me a little worried about its effects on the wood. I dont think it would set fire but could warp or split it and probably ruin whatever finish you use.
     
  14. jsnwhite619

    jsnwhite619 Friend of Leo's

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    I ran a 6v6 amp for a few hours with the back off to test it out and troubleshoot. PT was around 125 degrees, all the caps were around 100 degrees, and the tube power tube areas were got near the 250 degree range. Measured with an infrared thermometer.
     
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  15. A13X

    A13X TDPRI Member

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    Wow, thank you EVERYONE, I don't have enough time at this moment to go through and respond to each post individually.
    Seems like aluminum baking pan or something along those lines, is the way to go. I'll definitely be venting the electronics, and I guess if it's getting too hot I'll work on fans. I have some spare aluminum pickets that I'll use for extra support under the transformers.

    What about a safety ground for the chassis? Can I just attach a tin coated aluminum lug with an aluminum screw. And the run my copper ground to it? Or should I find someone that can weld/braze a ground stud to it?
     
  16. schmee

    schmee Doctor of Teleocity Silver Supporter

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    Tubes are the majority of heat. Transformers dont get hot much unless things are wrong. With the cheap chassis available now days at $40-100 with faceplates it's hard to think of building a chassis. A custom face plate could cost you $50 or more.
     
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  17. Bitsleftover

    Bitsleftover Tele-Meister

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    No way! I’m a UK A&C. Or EASA B1 in new money


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  18. Mongo Park

    Mongo Park Tele-Holic

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    I could see grounding things would be harder with wood.
     
  19. telemnemonics

    telemnemonics Telefied Ad Free Member

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    I get free sheet aluminum from roadside ditches and have scraps in the garage for whenever I need it.
    Theses nice sheets of aluminum have some obtrusive writing on them, but I just put it on the bottom or back.
    Stop, no parking, moose in road, stuff like that.
     
  20. telemnemonics

    telemnemonics Telefied Ad Free Member

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    Do those 300b amps really sound good?
    Or is it more that they look so cool?
     
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