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Always thought that it was the pins making contact with the sockets.
No that's the cause of crackling and static, eroded pins, hum comes from 6SN7 tubes, usually on the left side. I had one tube with hum go away in 4 hours, others after 48 and the longest a week later. All part of the fun with the Darkvoice. Slam in some nice tubes and you get rewarded though! All mentioned on the Original Post of this thread..
So I did some quick research after work and found this on the Woo Audio Site.
"What to do when my amplifier developed a light hum/noise?
Noises can come from many different places. e.g. power source, audio cables, environmental EMI. To test, please try the following.
- disconnect all cables from the amplifier.
- install ALL stock tubes.
- move amplifier to another area of the house. e.g. living room, kitchen countertop, office, etc. (This is important to isolate the amplifier from other components).
- keep cell phones, WiFi routers, powered hard drives and other high EMI devices away from the amplifier.
- connect AC power cord directly to a wall outlet (no conditioners or power strips).
- connect headphones to the amplifier and set volume to 11 o’clock position.
- listen through headphone. Do you still hear the hum?
If you still hear the hum, try a ground-lift adapter (for testing ONLY). If the hum goes away using the adapter, you have a ground-loop issue in the house. You can use a device called HUM-X".
I would ONLY try the suggested ground lift adapter if the hum didn't go away after some BURN IN. This from TubeDepot.com
The Benefits of Burn In Power Tubes
"New tubes have always sounded and performed better when burned in prior to final testing and installation. By running a tube at full operating voltages (and not just the 6.3 heater voltages) for 24 hours, the cathode is allowed to stabilize and any oxide contaminants on the metal surfaces evaporate and are collected by the getter. The burned in tube is "cleaner" inside and better able to reproduce sound.
For burned in power tubes, the initial matching is less likely to drift and rebiasing isn't needed. The stability is immediately apparent. And for preamp tubes, the improved tone is instantaneously accessible without having to wait for the tube to stabilize making "tube rolling" much easier. And the combined benefit, the burn-in process quickly weeds out weak and suspect tubes before they get into your equipment.
If you want the best for your equipment and your listening enjoyment, burned in tubes are the most effective methods to insure your satisfaction. You don't have to wait for the best".
And then there's this from TheTubeStore.com
Burning In 6SN7 Tubes for the Dark Voice 336SE Headphone Amp
POSTED BY JON @ THETUBESTORE ON JULY 7, 2016 IN AUDIOPHILE NERVOSA | 11,446 VIEWS | 36 RESPONSES
"If you have a Dark Voice 336SE headphone amp you likely had the same thought as many other owners. Why does such a nice little amp come with such poor tubes? Well most Chinese made amps do come with cheap Chinese tubes because they are readily available. Unlike some Chinese amps that use obscure tubes with limited or no western equivalents to upgrade to, the DV-336SE uses tubes that have many substitution/upgrade options. It’s most common to upgrade the 6SN7 tube. We won’t get into which tube sounds best in this article though. Rather I want to address the common problem folks find when installing their new or NOS 6SN7 tube. With rare exception, there is a noticeable hum in the left channel. This will occur with any 6SN7 tube. But the good news is that after burn-in they will become dead quiet again. Here’s what to do:
1. Power off the amp and remove the 6AS7/6H13C power tube. This will keep the unit from over heating during this burn-in procedure.
2. Install your new 6SN7 tube and power the amp on again.
3. Wait. And keep waiting. We find that by approximately 72 hours will do.
4. Power off and re-install the 6AS7/6H13C power tube.
5. Connect your favorite headphones and power the amp on.
You should find the hum in the left channel has completely disappeared. At the least you’ll notice it’s much quieter and likely only need one more day to get it completely quiet.
I realize you can modify the amplifier and add a couple capacitors to solve this but the instructions above will “fix” it for free so give it a try".
The modification mentioned here/above is the Fitz Mod. Replacing the cheap capacitors with nicer ones, kinda need some expertise on this one.
Hum is normal in other otl amps I've tried - it's an indication that your tube is in fact, genuine new old stock and hasn't been used. If the hum stays - that's another thing entirely!
Kinda just mentioned that above..
I'm a big fan of this amp. Definitely my go-to with my modified HD650s. A while back on Massdrop I put together a short list of my favorite tube pairings (power and driver) with pics for guidance. Thought it may be of interest. Click here
There are also a number of 6SN7 subs that are well worth checking out. I'll cut and paste something I posted on massdrop:
There are a number of tubes that you can sub for the 6sn7 with various adapters. I've tried a 12ax7 to 6sn7, a 6cg7 (the mini 9 pin version of the 6sn7) to 6sn7, a 12au7 to 6sn7 and a 6f8g or 6c8g to 6sn7. Wasn't crazy about the 12ax7 or 12au7 with adapters in the DV. The 6cg7 is an interesting tube. Most of the ones I tried were too bright, but I have a mullard and Amperex that sound fantastic.
The 6f8g was the tube prior to the 6sn7. I've just recently gotten into these tubes and they are quite impressive. Some people (with way more knowledge than me) claim they are better than the 6sn7. I have a Tung Sol VT99 (Military version of the 6f8g) that is the same tube as the famed 6sn7gt round plates. IMO, the vt99 is a better tube. The national union 6f8g is also amazing. Prices for the 6f8g tubes are generally much lower than the equivalent 6sn7 tubes (the adapter is only about $15). I got the Tung Sol VT99 (nos) for $25 a year ago. Unfortunately that particular tube has skyrocketed in the past year.. but you can still get them much less than the 6sn7 (plus they are gorgeous to look at).
Also worth noting, the 6f8g adapter will also work with a 6c8g. These tubes are even cheaper. Look for the national union JAN version (I just picked up a NOS for $15 shipped that sounds better than the NU grey glass in my photo above that cost me $70 for NOS). Another great 6c8g is the RCA round plates (also just got that NOS for $20 shipped).
Thanks for the tip, as some NOS 6SN7's are fetching crazy prices now. I lucked out on a 1954 Sylvania 6SN7GTA chrome top recently to pair with an RCA 6AS7 (black plates). Any power tube recommendations for the 6c8g's?
I snagged a chrome top sylvania off ebay for 8 bucks that sounds freakin amazing. Paired it with a ge 6as7ga that was 15 shipped. Such a good combo. I dont know if its a chrome dome or not. The chrome top almost reaches the bottom on one side, very uneven chrome job on it. What ever it is, it was a steal. Its by far my best sounding 6sn7. i also got a phillips jan 6080wc and a tung sol 7236 coming in. My HD6xx will be here monday. So much fun these tube amps are.
I'm so tempted with the 7236, rave reviews from everyone here so far. And congrats on the HD6XX.
Hi: The 50's vintage Sylvanias are generally excellent tubes and are usually very affordable (as you point out!). They are clear, punchy and dynamic. You may find them to be a bit bright with the 7236...but if you are using an unmodified HD6xx, that combination may be perfect. Just curious.....is it a GT, GTA or GTB (if you look at the top of the tube in the "chrome" part, there should be lettering specifying which variant it is). Also, what's the date code? You can find this on the black base. you should be able to see three vertically stacked numbers. The top number is the year (3 would represent 1953) and the bottom two numbers would be the week (so 332 from top to bottom would be 1953, 32nd week). Enjoy your new tubes and the HD6xx will bring out the best of your DV.
I HIGHLY recommend the 7236. The DV can sound "dark" (as many of stated)...especially with the HD650s. The 7236 is a very clean sounding tube and paired with the right driver tube can sound absolutely magical. Plus, if you are patient, you can usually get a 7236 for a very reasonable price (I've purchased a few in the $30 range).
I got my 7236 for 30 bucks. Date code is worn off on the 6sn7. It is a gt and it’s has the same vintage 50’s writing on it
Yeah, NOS prices are pretty absurd. Although there are still many bargains out there. Unless it's a really rare and special tube there's no point in spending lots of $ on a NOS (IMO). I have had very good luck with "used" tubes (that test well and come from reputable sellers).
Regarding power tube recommendations, it really depends on the type of 6c8g you get. I generally try to pair a warmer sounding power tube with a brighter sounding driver and vice versa. Here are some pairings that I use with a variety of 6c8gs
1. National Union 6c8g: this is currently my favorite 6c8g. very dynamic. reminds me of a sylvania vt231 but with more body. I would pair this with a warmer power tube like a Mullard 6080 or a Tung Sol 5998.
2. Ken Rad 6c8g: Like many Ken Rads, this has excellent bottom end and is a little warmer than the 6c8g. I would pair this with a livelier power tube like a 7236 or a Tung Sol 6AS7G (or even RCA 6AS7G)
The 6f8g is also a great buy and there's more diversity that the 6c8gs (although it's easier to get an inexpensive 6c8g). I JUST got a Raytheon VT-99 (the military spec version of the 6f8g) for $20....that was the starting bid and no one else bid on it. That's a phenomenal tube (very similar to the Raytheon vt231). Very energetic. Would pair well with any of the power tubes I listed above.
IMO the GTs are the best of the three variants (GT, GTA and GTB). You got a great deal on that.