If it is happening on different tubes, I would just replace it. Could be a short, could be a bad part, you would have to open it up to diagnose it, which would likely void any warranty, so best to just exchange it.
Darkvoice 336i & 336SE Tuberolling PartII
- Thread starter HeatFan12
- Start date
If it is happening on different tubes, I would just replace it. Could be a short, could be a bad part, you would have to open it up to diagnose it, which would likely void any warranty, so best to just exchange it.
therremans
1000+ Head-Fier
Most things can be fixed. First, where did you purchase the amp? I’m sure they will likely make it right for you. So you confirmed this is happening with both sets of tubes. What are the replacement tubes that you swapped in?
Galapac
1000+ Head-Fier
If the buyer bought it on drop they will take it back and send another out fairly quickly. They have good CS. eBay...not so much.
bcowen
Headphoneus Supremus
Okay, going to try to explain how you go about center-tapping and elevating the heaters of the stock DarkVoice.
Please read in full before making any changes, be sure to understand what you are doing before you do it. If you are unsure if what you have done is correct, take a photo and PM me or post in the thread and tag me.
Heater Center Tap
What you will need:
- 2x 100ohm 1/2 resistors (type does not matter, metal film would be fine).
- 1x 2K 1/4W resistor
- 1x length of 20AWG wire (solid or stranded does not matter)
1) Find the two points on the main PCB where the heater wiring is soldered, here.
2) Solder one end of a 100ohm 1/2W resistor to each heater winding pad. Twist together the opposite ends and solder them together, like the illustration below. This is the center tap point!
3) Break the ground connection between the 6SN7 heater and the ground bus below. This wire can simply be cut or desoldered and discarded.
If you are elevating the heaters, skip to step 6. If you are not, go to step 4.
4) Now connect a piece of wire from the new center tap point to the ground bus. This is the long, thin length of bare wire that runs throughout the chassis.
5) Because the power LED is run from the heater supply and we have just halved the voltage it sees, we must adjust the series resistance before the power LED. On the power LED PCB, there are two 2K resistors, one on top and one on the bottom. Add the additional 2K resistor in parallel with the top 2K resistor. This means the leads of the new resistor will be soldered to the same pads as the existing 2K resistor.
If you are not elevating the heaters, you are done, the hum should be improved but might not be completely eradicated.
Elevated Heater Supply
You should have just finished step 3 and created the virtual center tap and broken the heater ground connection at the 6SN7 socket. To elevate the heater supply, we just make a voltage divider from the B+ supply to reduce its voltage to our desired elevation voltage. Anything from 30V-60V will work fine. This elevated voltage will be applied to the center tap point.
Additional items you will need:
- 1x 220K 1/2W resistor (type does not matter)
- 1x 100K 1/2W resistor (type does not matter)
- 1x 10uF 250VDC electrolytic capacitor (these Vishay / Sprague axial caps will work fine: https://www.mouser.com/ProductDetail/Vishay-Sprague/TVA1504/?qs=sGAEpiMZZMvwFf0viD3Y3aqMjiJTbj4RWQfU45X0ilM=)
- 2x additional length of 20AWG wire (solid or stranded does not matter)
6) Find the below power supply capacitor, the second to last in the supply (note this can be done with either capacitor in this position, they are all in parallel). This is the point at which you will connect the voltage divider. The B+ at this point should be roughly 150V, although I would not be surprised if it varied between amplifiers given the quality of the transformer, the end result will be the same.
7) To the newly created center tap point (the junction of the two 100ohm resistors), solder one end of the 220K resistor, one end of the 100K resistor, the positive end of the 10uF electrolytic capacitor, and one end of a 20AWG length of wire.
8) Solder the other end of the 100K resistor and the negative end of the electrolytic capacitor to the ground bus, shown in step 4.
9) The other end of the 220K resistor must be connected to the positive end of the power supply capacitor shown in step 6. If the leads are long enough to reach from the center tap point to the positive terminal, it can be done this way. Otherwise, connect the other end using an additional length of 20 AWG wire.
10) Disconnect the power LED PCB from the ground bus, shown below. The wire can simply be removed from the PCB and the excess clipped.
11) The power LED PCB ground must now be brought to the center tap point so the power LED does not see the elevated supply DC offset. Connect the length of wire connected to the heater center tap to the power LED ground PCB pad.
The wiring should look like below, another crude illustration.
12) Lastly, as in step 5, the series resistance before the power LED must be reduced so the LED will light up. On the power LED PCB, there are two 2K resistors, one on top and one on the bottom. Add the additional 2K resistor in parallel with the top 2K resistor. This means the leads of the new resistor will be soldered to the same pads as the existing 2K resistor.
That's it, you should now have ~45VDC heater elevation, the hum present on any noisy tubes should now be gone.
LG, this is awesome. Thanks so much!
One question: if the heaters are currently over-voltaged (as in ~7v that seems to be the norm), do the resistance values you've indicated for elevating the supply bring that down to ~6.3v regardless of the existing voltage? Or do those values need adjusted depending on existing conditions? I mentioned before mine were at 6.95v, and IIRC you were measuring ~7.15v on the one you have. Thanks!!
The guide above excludes the heater over voltage issue. The same calculation that you linked in my DIY thread applies just the same, the resistors are in series with the tube heater wiring. You can attach those series resistors directly to the heater pads on the main PCB, then attach the two 100ohm center tap resistors directly to the voltage dropping resistors. Hope that makes sense, if not I can draw another diagram. That is what I have done in the modded DarkVoice in the picture below (the heaters are not elevated in this photo).
Actually, I'll just add them to the diagram, but note the values must be calculated.
bcowen
Headphoneus Supremus
The guide above excludes the heater over voltage issue. The same calculation that you linked in my DIY thread applies just the same, the resistors are in series with the tube heater wiring. You can attach those series resistors directly to the heater pads on the main PCB, then attach the two 100ohm center tap resistors directly to the voltage dropping resistors. Hope that makes sense, if not I can draw another diagram. That is what I have done in the modded DarkVoice in the picture below (the heaters are not elevated in this photo).
Actually, I'll just add them to the diagram, but note the values must be calculated.
Makes perfect sense. Thanks!
Damok
New Head-Fier
I bought it from Drop, it just arrived a few days ago. I will contact them and see what the return policy is, I have also heard their CS is pretty good. The replacement tubes I bought: United NOS 5998, RCA 6SN7GTB. I also bought Dual Socket thingy and 2x Sylvania 6J5GT's but I havnt tried that yet. The socket doesnt go all the way down so I am not sure if I need an adapter for it or whatever.
This. Is. Epic.Okay, going to try to explain how you go about center-tapping and elevating the heaters of the stock DarkVoice.
Please read in full before making any changes, be sure to understand what you are doing before you do it. If you are unsure if what you have done is correct, take a photo and PM me or post in the thread and tag me.
Heater Center Tap
What you will need:
- 2x 100ohm 1/2 resistors (type does not matter, metal film would be fine).
- 1x 2K 1/4W resistor
- 1x length of 20AWG wire (solid or stranded does not matter)
1) Find the two points on the main PCB where the heater wiring is soldered, here.
2) Solder one end of a 100ohm 1/2W resistor to each heater winding pad. Twist together the opposite ends and solder them together, like the illustration below. This is the center tap point!
3) Break the ground connection between the 6SN7 heater and the ground bus below. This wire can simply be cut or desoldered and discarded.
If you are elevating the heaters, skip to step 6. If you are not, go to step 4.
4) Now connect a piece of wire from the new center tap point to the ground bus. This is the long, thin length of bare wire that runs throughout the chassis.
5) Because the power LED is run from the heater supply and we have just halved the voltage it sees, we must adjust the series resistance before the power LED. On the power LED PCB, there are two 2K resistors, one on top and one on the bottom. Add the additional 2K resistor in parallel with the top 2K resistor. This means the leads of the new resistor will be soldered to the same pads as the existing 2K resistor.
If you are not elevating the heaters, you are done, the hum should be improved but might not be completely eradicated.
Elevated Heater Supply
You should have just finished step 3 and created the virtual center tap and broken the heater ground connection at the 6SN7 socket. To elevate the heater supply, we just make a voltage divider from the B+ supply to reduce its voltage to our desired elevation voltage. Anything from 30V-60V will work fine. This elevated voltage will be applied to the center tap point.
Additional items you will need:
- 1x 220K 1/2W resistor (type does not matter)
- 1x 100K 1/2W resistor (type does not matter)
- 1x 10uF 250VDC electrolytic capacitor (these Vishay / Sprague axial caps will work fine: https://www.mouser.com/ProductDetail/Vishay-Sprague/TVA1504/?qs=sGAEpiMZZMvwFf0viD3Y3aqMjiJTbj4RWQfU45X0ilM=)
- 2x additional length of 20AWG wire (solid or stranded does not matter)
6) Find the below power supply capacitor, the second to last in the supply (note this can be done with either capacitor in this position, they are all in parallel). This is the point at which you will connect the voltage divider. The B+ at this point should be roughly 150V, although I would not be surprised if it varied between amplifiers given the quality of the transformer, the end result will be the same.
7) To the newly created center tap point (the junction of the two 100ohm resistors), solder one end of the 220K resistor, one end of the 100K resistor, the positive end of the 10uF electrolytic capacitor, and one end of a 20AWG length of wire.
8) Solder the other end of the 100K resistor and the negative end of the electrolytic capacitor to the ground bus, shown in step 4.
9) The other end of the 220K resistor must be connected to the positive end of the power supply capacitor shown in step 6. If the leads are long enough to reach from the center tap point to the positive terminal, it can be done this way. Otherwise, connect the other end using an additional length of 20 AWG wire.
10) Disconnect the power LED PCB from the ground bus, shown below. The wire can simply be removed from the PCB and the excess clipped.
11) The power LED PCB ground must now be brought to the center tap point so the power LED does not see the elevated supply DC offset. Connect the length of wire connected to the heater center tap to the power LED ground PCB pad.
The wiring should look like below, another crude illustration.
12) Lastly, as in step 5, the series resistance before the power LED must be reduced so the LED will light up. On the power LED PCB, there are two 2K resistors, one on top and one on the bottom. Add the additional 2K resistor in parallel with the top 2K resistor. This means the leads of the new resistor will be soldered to the same pads as the existing 2K resistor.
That's it, you should now have ~45VDC heater elevation, the hum present on any noisy tubes should now be gone.
Galapac
1000+ Head-Fier
You will probably need a socket saver to elevate the socket enough for the 6J5GT adapter to work as the socket sits a bit low on the DV. Good luck on the return/replacement as it should not be an issue other than the wait.
I forgot to mention two benefits of the elevating heater mod thing...
1) the voltage divider will act as a bleeder resistor for the power supply and will discharge the capacitors when the amplifier is turned off
2) you can remove the electrolytic bypass capacitors from the 6SN7 cathodes from the Hum Fitz mod (did I say it right?)
1) the voltage divider will act as a bleeder resistor for the power supply and will discharge the capacitors when the amplifier is turned off
2) you can remove the electrolytic bypass capacitors from the 6SN7 cathodes from the Hum Fitz mod (did I say it right?)
Damok
New Head-Fier
I am such a screw up, I cant believe I made such a massive mistake... I was too busy trying to ensure the tube was centered left and right when socketing it I didnt pay attention to front and back and the NOS 5998 was not socketed properly. The girlfriend took a look at it for me and told me it didnt feel properly seated, now I am back to enjoying the music.
Ripper2860
Headphoneus Supremus
We've all been there, brother. 
bcowen
Headphoneus Supremus
I think it's technically the "Fitz mod" to address the hum, but close enough.
And I actually have all the necessary parts in stock. Well, the 10uF cap I have is 450v, but close enough (and it's only slightly bigger)...
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I have two quick questions about the center tap:
1 - the resistor at the LCD only impacts whether or not the LCD lights up, correct?
2 - two 2k resistors in parallel have a total resistance of 1k, correct? As such could I replace the upper 2k resistor with a 1k (as I don't have a 2k at my disposal)?
1 - the resistor at the LCD only impacts whether or not the LCD lights up, correct?
2 - two 2k resistors in parallel have a total resistance of 1k, correct? As such could I replace the upper 2k resistor with a 1k (as I don't have a 2k at my disposal)?
Correct and correct. Only suggested paralleling a second 2K for simplicity, but the other resistor could be removed and replaced.
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