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Triode 6g15 Build Hum

Discussion in 'Shock Brother's DIY Amps' started by amazingalf, Apr 9, 2020.

  1. amazingalf

    amazingalf TDPRI Member

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    I've dug a little deeper on the subject and it seems like the only draw back to using the 6A 1KV diode in this instance would be its size. I'd love to hear if anyone knows a bit more on the subject.

    EDIT: After learning a bit more about diodes I'm seeing that even the 1N4007 diodes are rated for 1KV. I think I was just thrown off by the size of these.
     
    Last edited: Apr 15, 2020
  2. tubeswell

    tubeswell Friend of Leo's

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    6A diodes are ideal for a hum loop blocker. (You want enough power handling so as to be at least double the draw on all the PT secondaries combined - to carry any forward/reverse current that appears in the signal path, to ground)

    The hum loop blocker schematic I uploaded earlier had 6A diodes indicated for this.
     
  3. amazingalf

    amazingalf TDPRI Member

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    After thinking and making a plan of attack I finally finished changing the 6g15 build over to full wave bridge rectification, installed insulated jacks and followed @tubeswell 's grounding scheme. I've gotta say, this thing is unbelievably quiet especially when compared to before. I just wanted to say thanks to everyone who offered input on this build.

    I can't wait til I can get some quality time with this tomorrow! I've attached some pictures of the final guts. I ended up using a dijon cap for the hum loop blocker since I had one kicking around.
     

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  4. BobSmith

    BobSmith Tele-Meister

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    amazingalf, Mr Ridesglide and moosie like this.
  5. amazingalf

    amazingalf TDPRI Member

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    I've been playing around with the reverb unit, but something seems a little off. I've taken a look at the reverb tank which was provided with the Triode USA kit and it is a 9BB2A1B. I looked at the specification sheet for this and it says that the tank has an input impedance of 190 Ohms. Shouldn't the tank input impedance match the output transformer? If so I believe that an 8 Ohm input impedance should be used.

    Was the wrong tank shipped with this kit? Should I try to get a tank like this to match the input impedance to the output transformer?

    https://www.amplifiedparts.com/products/reverb-tank-mod-4ab3c1b-long-decay-2-spring
     
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  6. Snfoilhat

    Snfoilhat Tele-Afflicted

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    Yes
    C1B if it's gonna lay in the bottom of the cab like it would in a combo amp. C1C if it's going to be attached to the 'baffle' of the cab.

    Edit: how does the unit behave with the medium input impedance reverb pan?

    There's a cool circuit for driving those with a 12AU7 if triode has you keep it

    Edit edit: I don't think anyone added this document yet. A classic! (PDF)
     

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    Last edited: Apr 23, 2020
  7. amazingalf

    amazingalf TDPRI Member

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    Thanks for confirmation Snfoilhat

    I've gotta say, my overall experience with the Triode kit has not been a positive one. Took several back and forth emails, multiple shipments and a lot of persistence to get all the parts in.
     
    Last edited: Apr 23, 2020
  8. amazingalf

    amazingalf TDPRI Member

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    Snfoilhat -That PDF is what made me realize something was wrong with the impedance! Its a good doc.

    With the medium input impedance reverb pan it just sounds like some thing is lacking. Almost like it is sucking some of the life out of the guitar. You notice it pretty quick as you turn up the mix control.

    I'm not sure if I'll even hear back from Triode this time around for a swap so I'll probably end up stuck with the 9BB2A1B. Guess I'll have to look into messing around with that and a 12au7.
     
    Last edited: Apr 23, 2020
  9. tubeswell

    tubeswell Friend of Leo's

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    1st thing I'd try is the correct pan. The poor idiot who had the job of packaging things up at Triode probably had no idea (or they were blind or working in the dark). Using the wrong impedance will rob you of optimum current (which is otherwise needed to drive the pan's input transducer) - like hooking up the wrong impedance speaker to an output transformer.
     
  10. amazingalf

    amazingalf TDPRI Member

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    I have no idea what is going on at Triode, but...

    Good news is they're shipping the correct pan. It's a horizontal mount accutronics one. I ordered a vertical mount MOD one as well from amplified parts. I figure this way I can experiment between the two!
     
  11. zook

    zook Friend of Leo's

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    I'd get the PT out of the inside of the chassis and mount it on the outside. I've had noise problems with them mounted inside.
     
  12. amazingalf

    amazingalf TDPRI Member

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    @zook I'm going to give it a shot wired inside for the time being, but I'll keep that in mind if I encounter any issues.

    Does anyone have opinions on vertical vs horizontal mount? How about reverb bags in a unit like the 6g15?
     
  13. zook

    zook Friend of Leo's

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    double post
     
  14. zook

    zook Friend of Leo's

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    The original was suspended by 4 springs against the front panel.
     
  15. tubeswell

    tubeswell Friend of Leo's

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    It depends on the type of inducers in your pan. Some inducers are made for horizontal mount pans, others are made for vertical mount pans. Your pan will work better if it's mounted the way that the transducers are designed to work. (Fender used vertical mount pans, so they could shove the pan into the front of the reverb unit cab)

    A reverb pan bag can be effective in dampening acoustic feedback from the pan, if that's a problem in your unit. Works best with a bit of corrugated cardboard on either side of the pan (inside the bag). Reverb pan feedback is typically a high-pitched constant ringing, a bit like microphonic pre-amp tube feedback, but not quite as 'howly'. If you get this noise, then putting your finger on the back of the pan, will quickly confirm whether it's the pan ringing or something else.
     
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  16. amazingalf

    amazingalf TDPRI Member

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    @tubeswell I should have been more specific, I was asking if folks had a preference sound wise between the two types when mounted in the appropriate position.

    I got the new pan from Triode today, a Belton 4AB3C1B and installed it horizontally in a Fender bag. This build has finally come to life! I'm really digging all the dramatic reverb that I can get out of it!

    I still have a MOD vertical mount pan coming in as well. My plan is to record some clips with each and upload.

    Thanks again for all the help! Are there any cool or interesting mods for this circuit that folks recommend?
     
  17. bieworm

    bieworm TDPRI Member

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    TS , I didn't ro the 6G15, but went for the lamington reverb unit. It sounds great, but buzzes like crazy if I plug it in front of my amp. It's fed by a 1600mA 12VAC wall wart ( by design) so the ground us lifted. I star grounded every ground connection, so all ends up at one point. Is ground loop likely that way? I still think its ground loop...
     
  18. bieworm

    bieworm TDPRI Member

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    TS , I didn't ro the 6G15, but went for the lamington reverb unit. It sounds great, but buzzes like crazy if I plug it in front of my amp. It's fed by a 1600mA 12VAC wall wart ( by design) so the ground us lifted. I star grounded every ground connection, so all ends up at one point. Is ground loop likely that way? I still think its ground loop... IMG-20200711-WA0000.jpeg
    I had to disconnect the pilot light, and that reduced some hum. I found out it added hum when I held metal objects between the lightbulb and the output jack and the hum was less doing that. I will put a 12v lightbulb and connect it to the heater wiring.
     
    Last edited: Jul 17, 2020
  19. tubeswell

    tubeswell Friend of Leo's

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    Yep a ground loop will occur with any separately powered reverb unit where you need to have a 3-prong mains plug with a safety ground.

    The 'solution' is to elevate the signal ground in the reverb unit (e.g. by using a hum-loop blocker), whilst keeping the safety ground securely attached to the chassis.

    Also, as reverb circuits are inherently more noise-sensitive (high S:N ratio in reverb recovery stage), you need to pay attention to separating the various high-current and low-current ground returns so that you don't have low-current returns riding 'on-top-off' noisier high-current returns (e.g. by using galactic grounding with one grounding point. This is a bit different from a Star ground) See Merlin Blencowe's grounding article.

    You also should ideally follow good lead dress practices - avoiding unwanted coupling from mixing up AC mains (or PT) wires with signal wires, separate the high VAC signal wires from sensitive pre-amp signal wires, shielding grid wires and vol/tone pot input wires etc. Grid stoppers on signal grids to suppress RF etc
     
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