Heater wiring to tube first

Discussion in 'Amp Tech Center' started by tele_savales, May 23, 2020.

  1. tele_savales

    tele_savales Tele-Holic

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    Is there a huge difference in hum reduction or any other benefit to wiring the 6 volt tap to say a power tube, then to the pilot light, instead of just wiring the tap to the pilot light first?
    Thanks!
     
  2. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Running to the first power tube first and then running a separate thin wire to the pilot light greatly reduces the current pulsing through the pilot light wire which typically flies up away from the chassis so it should be quieter.
     
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  3. tele_savales

    tele_savales Tele-Holic

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    Thanks a bunch. Btw this is on your JCM800 design. I'm re-doing the heaters because I am not in love with the wire I initially picked, but I've fired it up and it sounds killer. I'll post some pics shortly.
     
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  4. tele_savales

    tele_savales Tele-Holic

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    63CB209B-54CA-4135-A55B-D85DCD6A232A.jpeg
     
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  5. robrob

    robrob Poster Extraordinaire Ad Free Member

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    With flying heater leads like those in your amp the difference between running first to the pilot light or first power tube will probably be minimal. For amps with the heaters down along the chassis it "should" be slightly quieter.

    Your heater wires look just fine to me. A tighter twist isn't required. I would not redo them.
     
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  6. tele_savales

    tele_savales Tele-Holic

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    Too late. For one, I couldn’t twist that heater wire any tighter because even at super slow speed in my drill chuck, the cloth started to shred which is a new on on me, so I twisted them by hand. Secondly I had no idea how fat that cloth wire was and it was very hard to get in and safely clip my multimeter leads esp to pin 3. Maybe I’m getting more anal but I just couldn’t let it stay the way it was. Also the ac power wiring was in the way and I desoldered and rerouted that. B26DD0C5-7BB8-49DF-9009-47A3AC31D819.jpeg 7B986E3E-2732-4744-A496-30EC09C51F21.jpeg 84F32AF6-E3FF-4F03-8343-D65B2A5459A3.jpeg 0AB8EC4C-1136-43BD-9059-8512BCC69FB4.jpeg
     
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  7. tubejockey

    tubejockey Tele-Holic

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    If you're trying to reduce hum, reference the heaters to a DC voltage higher than the cathodes. Or better yet, rectify your heater supply, filter it and regulate it before it supplies the first couple preamp tubes. Look at some Rivera schematics.
     
  8. tubelectron

    tubelectron Tele-Afflicted

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    On moderate power and gain amps, here's what I do :

    [​IMG]

    On higher power and gain amps, I replace the 2x 100R resistors by a 220 to 470R adjustable pot.

    It's really important to place those 2x 100R resistors or the hum balance pot accross the 1st preamp tube, for a maximum heater hum nulling efficiency.

    I invented nothing : it's what you find on a 70s SF Twin-Reverb.

    And yes, I connect the pilot as on your last picture, @tele_savales.

    But it's me, OK ? :D

    -tbln
     
  9. tele_savales

    tele_savales Tele-Holic

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    There is a heater elevation in Robs design. Also, the transformer has a center tap for the heater winding. I have also used a virtual center tap w resistors to ground, and a humdinger pot in other amps.

    I just knew that I was going to replace the heater wire anyway because I a) didn't like the way it looked and b) the thickness of the shielding made it hard for me to access the power tubes when taking measurements, and what I wanted to know was if there was a major benefit to wiring the 6v tap directly to a power tube first instead of to the lamp like usual.

    I don't notice a massive difference as the amp is pretty quiet, but I am happy w how it turned out.
     
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  10. tele_savales

    tele_savales Tele-Holic

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    Looks mighty clean.
     
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  11. King Fan

    King Fan Poster Extraordinaire

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    Good question, @tele_savales ... and good answers from others here... and in your posts. I agree, drill twisting cloth-covered heater wiring is asking for trouble.

    So if I'm seeing it right, the heater sort of sits at the end of a spur siding? I guess depending on bulb location you could anchor your spur line on almost any tube? Power tubes preferred, of course, if nothing else because (next question)...

    Is there a problem fitting 3 wires into the socket lugs? That is, 1) fat wire from PT, 2) wire to spur, 3) wire on to next socket?

    Final question: How many amps does the bulb draw? For T-47 bulbs I see one site say they're 0.15A. 150 mA?
     
  12. tele_savales

    tele_savales Tele-Holic

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    Fitting the 2 sets of wires plus the heater winding wires was easy on v5 because the super nice tube sockets I got have two large holes on each pin, so I put the leads from the pt into the lower set of holes, and the heater wires to the lamp and v4 into the upper holes. I wish the preamp sockets were so easy. I have no idea how many amp the light bulb draws.

    I'm not sure what you mean by spur siding. I've never heard that in regards to amp circuitry but it sounds like railroad terminology.

    That fat cloth covered wire, I think that someone could make use of it, but it gave me a lot of headaches. You cant strip it with those automatic strippers because it doesn't grab the sheath, it's really hard to hold onto when you try to strip it with a regular stripper because its too smooth and soft to keep from slipping, and it doesn't hold its shape at all. I didn't complain to the vendor because it's not really their fault, I just didn't really know what I was buying.

    Short story long, I will never use stranded wires for filaments ever again. I do try to repurpose wire as much as possible, there's a couple pieces of 70's silverface wire in this chassis, so I am sure I can use it for something else at some point.
     
  13. tubelectron

    tubelectron Tele-Afflicted

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    Thanks ! ;)

    [​IMG]

    [​IMG]

    IMHO, it's not a good idea regarding hum...o_O

    I'd rather discard cloth covered wires, instead ! ;)

    But it's me, OK ? :D

    -tbln
     
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