New 5e8a build

Discussion in 'Shock Brother's DIY Amps' started by mgrossm, Jul 27, 2021.

  1. mgrossm

    mgrossm Tele-Meister

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    Just started a few days ago on this after getting lots of feedback on grounding schemes and setting up the bias...I'm sure there will be some more questions, but wanted to document it so far. This is my 4 or 5th build after a 5f8a, 5e3, 5f6a and redoing one of those etc...

    This build is using:
    PT MOJO 752
    OT MERCURY low powered tweed
    Choke weber wo14684 (5-8H @ 200ma, 125 ohms)

    I've kinda gone all out nuts collecting parts for this...have nos eby sockets, bradley resistors, Jupiter caps, nos rectifiers, nos rca 6l6gcs (or close), fat jimmy speakers ( one alnico one ceramic) etc.

    So far I've wired up part of the pt and heater filament wires....I put rubber grommets in the first 2 sets of preamp screw holes and had to enlarge the holes with a 3/16th bit to do so but it worked nicely. Posting pics now. Will continue to update.
     
  2. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Read this:
    http://www.valvewizard.co.uk/heater.html

    heater10.jpg

    The heater wires are twisted for a reason other than to hold them in place. The red wire with blue stripe will interfere when it is braided in with the heater wires.
     
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  3. mgrossm

    mgrossm Tele-Meister

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    I typically have wired it in the past the way valvewizard has suggested. This build i was trying to make it as vintage correct as possible as ridiculous as that seems. Did original fenders have issues with hum due to their heater wiring? I ask because in the pics I've been referencing from old amps this is how they did it and also how clark tends to do it. Fender also would twist the bias wire in with the 6.3 filament wires then drop it down on the board...donyou think I just have it braided too tight? Here are some pics to show you what im talking about.

     
  4. mgrossm

    mgrossm Tele-Meister

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    The only parts of the heater wires that aren't twisted are the ones running to the same pin so there wouldn't be any cancelation anyways. The wires that do need to cancel each other are twisted though. If that makes sense.
     
  5. Wally

    Wally Telefied Ad Free Member

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    Doesn’t the valve wizard advise to bring the heater supply wires to the pins over the top of the socket rather than looped around the socket….as shown in lowerleftcoast’s post above??
     
  6. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    I am no expert on the 5E8A. AFAIK the heaters were all wired with a single 6.3V wire to the sockets with a corresponding terminal soldered to the chassis. (Similar to a couple of the pictures you provided.) There would be no benefit to twisting the heater wires when using this method.

    My cursory search for original 5E8A images revealed nothing. I suspect the bias wire bundled with the heater wires was not how it came from the factory. I will defer to more knowledgeable shock brothers to opine.

    Did original fenders have issues with hum due to their heater wiring?

    Imo, they did, or maybe I should rephrase that. They would be quieter with a modern heater wiring scheme. The hum from an original heater wiring scheme may not be loud enough for a guitarist to call it an issue.

    do you think I just have it braided too tight?

    Ime braiding the wire does not provide the canceling properties that twisting will. From what I have seen of vintage Fender wire twisting, there was little to no *tight* wire twisting.

    I can't recall the source but I read a college thesis paper on the subject. The conclusion was a certain pitch was favorable for cancellation. It was a tight wind similar to most neatly laid out builds we see these days.

    All that said there are amps that do not twist the heater wire. They keep the wire separated by a distance to have it not interact with other wires.
     
  7. zeppelinofled69

    zeppelinofled69 Tele-Meister

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    I appreciate the knowledge behind the twisting pairs and also understand that I am just a novice at this compared to most, but the twisted heaters seems to be just another one of those grounding scheme type things where everyone has their way of doing things. In principle it makes sense to me, but the real-world benefits don't seem to be in line with the amount of people posting that picture of the sad and smiley faces. At the very least, I think the amp being built will dictate what makes sense to do, like flying leads in a blackface style chassis vs tight to the chassis lip like in Tweeds.

    I have had quiet builds all around with almost every heater twist method under the sun, including completely untwisted runs like in the SLO 100.

    I guess I'm just trying to say... while best practice may be ideal, sometimes it's not the best way to get the job done in that particular application.
     
  8. mgrossm

    mgrossm Tele-Meister

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    I'm certainly no expert here having only built about 5 amps now. I've floated heaters and also did an amp where I first floated heaters above power tubes then transitioned the heaters to preamp tubes against the chassis as in this build. It seems like its an issue of always room for improvement...by blackface models fender was floating them right? Maybe there was more space or maybe they found it was quieter?

    I didnt notice a difference but did find it was easier to deal with the rest of the wiring without having to work around the floating heaters...and I figured if clark amplification (and fender for that matter) didn't go broke i should be ok....of course I guess I'm taking the risk that I could turn the suckered on and be faced with terrible hum and have to rewire....but I also confess that I really also like the way it looks. It also makes sense from a cancelation perspective as the wires that need to be cancelling each other are in fact twisted th...the only ones that aren't are the short lengths running to the same pins which have same polarity etc..

    Regarding the bias tap wire it looks like fender did in fact consistently run it with the heater wires off the PT from the beginning (pics are of original twins and bassmans)...I think I braided mine too tightly so I took out the bias wire and just loosely wrapped it around...I think its a nice way of routing that wire.

     
  9. Wally

    Wally Telefied Ad Free Member

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    Note the difference in these three approaches. The Valve Wizard suggests that the connections to the pins should be made from the pair being brought above the socket. This does not necessarily entail running the twisted pair running above the sockets in between the sockets as in the 6G/BF/SF Fenders.
     
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  10. zeppelinofled69

    zeppelinofled69 Tele-Meister

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    Wally, I see your point but isn't it varying degrees of the same thing? You still wind up with a section of one leg of the heater that will always be untwisted, so this is like mitigating an inch of untwisted wire. I have also always thought it would be really easy to burn insulation when they are run like that through the socket, but I have meat-hooks for hands, so YMMV.

    My SLO build pictured below has the heaters run as bus wire right along the sockets with no twist and that amp is actually waaay quieter than I thought it would be for such a high gain amp.
     

    Attached Files:

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  11. zeppelinofled69

    zeppelinofled69 Tele-Meister

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    And to be clear, I am not calling anyone nitpicky or throwing gruff... I am honestly curious if anyone has experienced this particular topic having as much of an impact as folks say it does.
     
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  12. schmee

    schmee Doctor of Teleocity Ad Free Member

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    The twist can be very minimal. It's function is just to keep from two parallel wires creating interference. Everyone seems to want a tight overtwist. Many old amps, like Hammond, lay the heater wires right on the chassis, I have no problem with it.
     
    Last edited: Jul 27, 2021
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  13. Wally

    Wally Telefied Ad Free Member

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    Zep, I defer to the Wizard’s point of view. And…in this lower gain amp, noise might not be a problem. Such noise could probably seen on a scope, but the average player would not notice anything????? If I were building such an amp, I would build the heater filament wiring as shown in the third example. Sometimes in it not how much wire but where that wire is that can introduce or eliminate noise, ime.
    As for Soldano, I was shocked when I opened up a Hot Rod 50 and saw those paralleled heater filament ‘providers’. I had never seen or heard of such an approach, but I had to accept that he knew what he was doing because that is a hig( gain amp and there is no spurious noises to be found, ime.

    As for twisted pairs, here is an interesting analysis.
    https://www.diyaudio.com/forums/tubes-valves/211731-heater-wiring-bad-ugly.html

    In there, they mention that the twisting accomplishes an important task by stabilizing the wires…preventing movements which can
    Produce ‘noise’ by inducing an unwanted signal. So, in thos Soldano, that sizable wire that he used in those parallel supplies were designed NOT to move.
     
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  14. zeppelinofled69

    zeppelinofled69 Tele-Meister

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    Thanks Wally.

    One thing that dawned on me as I have been thinking about this is there is one thing that can't be argued about the wizards approach... If the heater wires run through the socket as advised, any wires approaching the socket pins with signal or otherwise won't have to run over the top of the heaters to get to the pin.

    I read the valve wizards page on heaters, and I have never heard of a hum loop, but I can imagine anything passing over a loop of wire with AC current would have adverse affects on the noise floor.
     
  15. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    The three different approaches shown in the valve wizard photos are not so much about how the wire is twisted or if an inch or two is not twisted. The idea is to mitigate the effect of the electromagnetic field around the associated wiring. Many builds have had this be an issue but repositioning the wiring can lessen the hum.

    The SLO wiring keeps distance between the wires so the EMF is not coupled with the other wiring of the tube.

    From your post above, I see you can envision the problems with the tube's approaching wires so I can stop writing. Hah.
     
  16. Wally

    Wally Telefied Ad Free Member

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    schmee, that diy audio link points to another reason for the twist…..reduction of movement which can induce noise. That was a new one for me.
     
  17. mgrossm

    mgrossm Tele-Meister

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    Well I've probably gotten away with a lot...I'm definately not the cleanest builder. 1st pic was my 1st build...5f8a with floating heaters. Very quiet. 2nd is a 5f6a 2x12 in a chassis that wasn't exactly spec and forced some odd choices in terms of wiring...I ended up floating some heaters and laying some on the chassis. The first input signal wires are coming right off the resistors from the board to the input tube. It's pretty darn quiet...for me at least.
     
  18. schmee

    schmee Doctor of Teleocity Ad Free Member

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    Good point, I could see flying heater wires picking up something harmonic I suppose!
    Can we use this? I visualize a box with switching to different length heater wires for different harmonics...? :eek::lol:
     
  19. Paul G.

    Paul G. Friend of Leo's

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    Don't forget, blonde, black and silver amps have shielding on the top of the cabinet as well. The raised heaters are completely enclosed in a Faraday cage, and are running close to the shield.
     
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  20. Tom Kamphuys

    Tom Kamphuys Tele-Holic

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    First of all, if a particular way of heater wiring dressing works for you, I'm fine with it.
    Below are some explanations of the physics involved. They're about the principle, not about their quantity, let alone whether or not you find their resulting hum disturbing.

    There are two statements I have troubles with:
    1) everything that needs twisting is twisted.
    That is not the case. The current through the tube completes a loop:
    IMG-20210727-WA0005.jpg

    This loop is like a small transformer and induces current in nearby wires (and in the tube itself?).

    2) the wire to the same pin doesn't cancel.
    The current is going to that pin, and moving back to the twisted central wires. That means the current is in opposite direction (apart from the current going through the tube as discussed in 1) ) and does cancel.
    IMG-20210727-WA0006.jpg


    Well, actually you want the (fields from the) wires to interfere, destructively. They do that when the distance from a signal wire under the influence of them, to the two heater wires is equal, because the current in flowing in opposite directions. Keeping the pair of heater wires close helps, twisting them helps a bit more as both wires take turn (pun intended) in which one is closest to the signal wire, averaging out their hum fields even more.
     
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