Yup, Another One... Kraken 50 Build: Round II

Marshall Amp Discussion

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V2
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Re: Yup, Another One... Kraken 50 Build: Round II

Post by V2 »

FourT6and2 wrote: Sat Jul 29, 2017 1:14 am I really love having a power transformer with solder tags. Makes wiring it up much cleaner. Wish more companies would do it this way.
What gauge wire are you using on the primary side?
Last edited by V2 on Tue Aug 08, 2017 2:23 am, edited 1 time in total.
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JazzGuitarGimp
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Re: Yup, Another One... Kraken 50 Build: Round II

Post by JazzGuitarGimp »

Nice colors going on inside that chassis. I hope you're planning on contrasting all those nice blue and violet wires with some snazzy orange and yellow...
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Re: Yup, Another One... Kraken 50 Build: Round II

Post by FourT6and2 »

JazzGuitarGimp wrote: Mon Jul 31, 2017 8:25 am Nice colors going on inside that chassis. I hope you're planning on contrasting all those nice blue and violet wires with some snazzy orange and yellow...
Nah lol. Purple all the way.
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Re: Yup, Another One... Kraken 50 Build: Round II

Post by FourT6and2 »

Some more progress today. This is the part where everything's a hot mess lol.

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FourT6and2
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Re: Yup, Another One... Kraken 50 Build: Round II

Post by FourT6and2 »

Home stretch.

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Re: Yup, Another One... Kraken 50 Build: Round II

Post by FourT6and2 »

So, amp sounds fantastic. Love the tone. But I do have a small hum problem exacerbated by Gain 2 pot and Bright 2 switch. Gain 1 and Bright 1 don't affect the hum at all. I can turn them up to 100% and no hum. But Gain 2 adds hum as you turn it up. And Bright 2 switch brings in more hum. Hum isn't that bad until the master volume is up around 2:00 - 3:00. Hum seems to be tied to V1b or V2a somewhere. I can't seem to track it down. Someone else on another site seems to think it's cathode follower filament hum. But I don't think that's the case. My other builds are super quiet and are the same circuit.

I've eliminated a tube problem. So it's not that.

Not a component problem (mislabeled part, mistaken values, etc.). I've eliminated that.

Not a grounding problem as far as I can tell. But I did ground this build a bit differently than the other one that's quiet. Typically, this circuit is grounded as follows:

1. PT CT to chassis star ground.
2. Heater CT to chassis star ground.
3. Bias circuit/pots to chassis star ground.
4. Reservoir filter cap negative terminal to screen cap negative terminal. Screen cap negative terminal to chassis star ground.
5. Preamp and pots and input jack all grounded to floating bus bar on turret board. Floating bus bar has one wire to chassis star ground.
6. OT comm to output jack negative. All output jacks and FX loop negative terminals share a bus bar and go to a local chassis ground.

In this build, I did it like this:

1. PT CT to reservoir filter cap negative terminal.
2. HT CT to chassis star ground.
3. Bias circuit/pots to chassis star ground.
4. Screen cap neg. terminal to reservoir neg. terminal.
5. Preamp floating bus to screen cap neg. terminal.
6. Reservoir neg. terminal to chassis star ground.
7. OT comm wired the same as before.

So in this version, the reservoir filter cap neg. terminal serves as floating star ground, which then goes to chassis ground with one wire. Instead of all the individual nodes going to chassis ground with separate wires.
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martin manning
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Re: Yup, Another One... Kraken 50 Build: Round II

Post by martin manning »

What is the difference between "PT CT" and "HT CT" in the second scheme? Is "HT CT" heater CT?
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Re: Yup, Another One... Kraken 50 Build: Round II

Post by martin manning »

See comments below...
FourT6and2 wrote: Sun Aug 20, 2017 1:47 pmIn this build, I did it like this:

1. PT CT to reservoir filter cap negative terminal. Good
2. HT CT to chassis star ground. If this is heater CT, good
3. Bias circuit/pots to chassis star ground. Chassis star is probably ok, or ground with power tube cathodes
4. Screen cap neg. terminal to reservoir neg. terminal. Take this to chassis star ground or ground with power tube cathodes
5. Preamp floating bus to screen cap neg. terminal. Ground this with input jacks. I think this is where the issue is
6. Reservoir neg. terminal to chassis star ground.Good
7. OT comm wired the same as before.Good
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Re: Yup, Another One... Kraken 50 Build: Round II

Post by FourT6and2 »

martin manning wrote: Sun Aug 20, 2017 1:52 pm What is the difference between "PT CT" and "HT CT" in the second scheme? Is "HT CT" heater CT?
Typo. HT should be heater.
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Re: Yup, Another One... Kraken 50 Build: Round II

Post by FourT6and2 »

martin manning wrote: Sun Aug 20, 2017 2:07 pm See comments below...
FourT6and2 wrote: Sun Aug 20, 2017 1:47 pmIn this build, I did it like this:

1. PT CT to reservoir filter cap negative terminal. Good
2. HT CT to chassis star ground. If this is heater CT, good
3. Bias circuit/pots to chassis star ground. Chassis star is probably ok, or ground with power tube cathodes
4. Screen cap neg. terminal to reservoir neg. terminal. Take this to chassis star ground or ground with power tube cathodes
5. Preamp floating bus to screen cap neg. terminal. Ground this with input jacks. I think this is where the issue is
6. Reservoir neg. terminal to chassis star ground.Good
7. OT comm wired the same as before.Good
For #5, it's the same as my first build the input jack and pots and turret board are all grounded to the same bus bar, that then goes to the screen cap negative lug, which goes to reservoir cap neg. lug, then to ground.
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Re: Yup, Another One... Kraken 50 Build: Round II

Post by martin manning »

Are the pot cases grounded securely? Maybe try clipping a lead to the ground bus and touching it to the case of the pots that gets noisy turned up. Are you observing this with the amp open? Any noise sources like dimmers, fluorescent lights, etc. nearby?
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Re: Yup, Another One... Kraken 50 Build: Round II

Post by FourT6and2 »

martin manning wrote: Sun Aug 20, 2017 5:08 pm Are the pot cases grounded securely? Maybe try clipping a lead to the ground bus and touching it to the case of the pots that gets noisy turned up. Are you observing this with the amp open? Any noise sources like dimmers, fluorescent lights, etc. nearby?
Yeah, I've tried that trick with the pot casings. They're all grounded fine.

I have three of these amps. Side by side. In the same room. Turned on. This is the only one that's noisy. So it's not environmental.
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Re: Yup, Another One... Kraken 50 Build: Round II

Post by martin manning »

Where does the top of the gain 2 pot connect? Seems like that is the source of the hum. Is there a schematic for this somewhere?
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Re: Yup, Another One... Kraken 50 Build: Round II

Post by FourT6and2 »

martin manning wrote: Sun Aug 20, 2017 5:56 pm Where does the top of the gain 2 pot connect? Seems like that is the source of the hum. Is there a schematic for this somewhere?
I'm still a total noob at this, so hopefully the schematic is correct: https://orig15.deviantart.net/ede0/f/20 ... bkjpxy.jpg
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Re: Yup, Another One... Kraken 50 Build: Round II

Post by martin manning »

Ok, thanks. So, if you ground the top or wiper of the Gain 2 pot, does the hum go away? The h-k insulation in the CF triode (V2B) might be under a lot of stress (don't know the voltage there), but if you can kill the hum by grounding upstream of that it's ok, at least for now. You said you swapped tubes? which ones, and you swapped for the ones in one of the quiet amps?
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