This tube was sold to me on eBay as a Shuguang 6922. However, using it in my valve-buffered chip amp, it produced an unexplained positive bias. Some kind folks over in the chip amp forum suggested that I ask here for help identifying the tube, which is not clearly labelled. The original markings have mostly worn off. On one line, I can make out the characters "6N". On the next, "722".
My original discussion about my amp build took place here http://www.diyaudio.com/forums/showthread.php?s=&postid=1860120 .
I was always slightly suspicious of this tube - Shuguang ones go extremely cheaply on eBay. The seller was in Taiwan. They did have 100% positive feedback.
Really appreciate any help you can give me
My original discussion about my amp build took place here http://www.diyaudio.com/forums/showthread.php?s=&postid=1860120 .
I was always slightly suspicious of this tube - Shuguang ones go extremely cheaply on eBay. The seller was in Taiwan. They did have 100% positive feedback.
Really appreciate any help you can give me
Attachments
http://enshuguangtubes.chsee.com/oldchsee/shuguangtubes/userViewSitcomCls.asp?SitcomClass=1520
There are 8 pages of power and signal tubes which are listed on shuguang's site.
The 6922 is not listed.
6DJ8, ECC88 and 6N23P are subs for the 6922. However, none of these tubes are listed as being in current production on shuguang's site. Shuguang probably makes alot of tubes which they do not list on their site, so it is possible that you do have a 6922. However, I think it likely that you have another (non-6922) twin triode.
You could get a NOS or current production 6922, 6DJ8, ECC88, or 6N23P, then test the behavior of the known to be 6922 with the tube you have now.
There are 8 pages of power and signal tubes which are listed on shuguang's site.
The 6922 is not listed.
6DJ8, ECC88 and 6N23P are subs for the 6922. However, none of these tubes are listed as being in current production on shuguang's site. Shuguang probably makes alot of tubes which they do not list on their site, so it is possible that you do have a 6922. However, I think it likely that you have another (non-6922) twin triode.
You could get a NOS or current production 6922, 6DJ8, ECC88, or 6N23P, then test the behavior of the known to be 6922 with the tube you have now.
The 6N1 is not listed in current production, but it was produced before, and it is billed as a sub for the 6922 and the 6DJ8. 6N1 is very likely the tube that gaplessophile has.
http://analogmetric.com/forum/viewthread.php?tid=233
Note: the page says the 6N1 is "Compatible with: 6922 and 6DJ8.", not specified as an exact sub. As always, buyer beware.
http://analogmetric.com/forum/viewthread.php?tid=233
Note: the page says the 6N1 is "Compatible with: 6922 and 6DJ8.", not specified as an exact sub. As always, buyer beware.
gaplessophile said:
Whoa, time out. Why do you think you need a new tube? This is for one of those valve buffered gainclones, right? A 6N1 will make a perfectly satisfactory cathode follower, especially since it's only driving the input of a chip. Just make sure your filament transformer can deliver the extra heater current.
EDIT: as for the "positive bias" you mention, it sounds like you wired it wrong.
The Shuguang 6N11 is equivalent to the 6922. To check if you have the 6N1 or 6N11, measure the heater current and you will be able to confirm. I cannot remember the exact current, but the 6N1 is higher than the 6N11. The 6N1 has similar current as the 6N1P, and the 6N11 has similar current to the 6922.
I have used a lot of 6N11. It is a robust tube, but I prefer the sounds of the NOS 6922 or equivalents. It is not a bad sounding tube. Just a matter of taste. And it is a highly regarded tube in China.
6N1 sounds slightly better in tube gainclone from my experience. Again, just a matter of taste.
I have used a lot of 6N11. It is a robust tube, but I prefer the sounds of the NOS 6922 or equivalents. It is not a bad sounding tube. Just a matter of taste. And it is a highly regarded tube in China.
6N1 sounds slightly better in tube gainclone from my experience. Again, just a matter of taste.
Oh, that's good news then! Unfortunately though, I really cannot figure out this positive bias issue. I'm convinced I haven't made a mistake with the wiring, since I've checked it again and again, and received some help over at this thread in the chip amp forums http://www.diyaudio.com/forums/showthread.php?s=&threadid=145804.
To quickly sum up the problem, the grid and cathode both have negative voltages on them (below the 0V ground). My power supply is balanced to within 0.1 V (about +-35V). The problem is the same on both channels, so it's unlikely that a stray wire could be causing the problem.
I am using the same power transformer for the valve and the chip amp circuitry, but I do have separate rectifier bridges and of course capacitors for each channel of each stage (4 rectifier bridges total).
The following is copied from a post of mine in the other thread:
"To try to further isolate the problem, I disconnected the valve circuit from the chip amp circuit - cutting off from the 3u3 capacitor onward. I also cut off everything from the grid pin of the valve. Under these conditions, cathode voltage was approximately -25 V, and grid voltage was approximately -12 V.
I then connected a 30k resistor from the grid to ground. Grid and cathode voltages were now between -2 V and -3 V."
I very closely followed this design here http://www.customanalogue.com/diytubegainclone/index.htm.
Power supply and wiring diagrams are here http://www.customanalogue.com/diytubegainclone/ps.htm.
My heater filament supply seems to be providing enough current. It's a DC regulated supply which puts out 5.95V. When the tube is plugged in, this voltage does not drop, suggesting that there is enough current available.
Would be really grateful if anyone could spot what I'm doing wrong!
To quickly sum up the problem, the grid and cathode both have negative voltages on them (below the 0V ground). My power supply is balanced to within 0.1 V (about +-35V). The problem is the same on both channels, so it's unlikely that a stray wire could be causing the problem.
I am using the same power transformer for the valve and the chip amp circuitry, but I do have separate rectifier bridges and of course capacitors for each channel of each stage (4 rectifier bridges total).
The following is copied from a post of mine in the other thread:
"To try to further isolate the problem, I disconnected the valve circuit from the chip amp circuit - cutting off from the 3u3 capacitor onward. I also cut off everything from the grid pin of the valve. Under these conditions, cathode voltage was approximately -25 V, and grid voltage was approximately -12 V.
I then connected a 30k resistor from the grid to ground. Grid and cathode voltages were now between -2 V and -3 V."
I very closely followed this design here http://www.customanalogue.com/diytubegainclone/index.htm.
Power supply and wiring diagrams are here http://www.customanalogue.com/diytubegainclone/ps.htm.
My heater filament supply seems to be providing enough current. It's a DC regulated supply which puts out 5.95V. When the tube is plugged in, this voltage does not drop, suggesting that there is enough current available.
Would be really grateful if anyone could spot what I'm doing wrong!
Sorry, I wasn't clear enough. Thanks analog_sa for helping explain the problem
The amp does work, but due to the voltage on the grid, I get crackling and temporary DC offset when I turn the volume pot. Also, voltage is being applied back to my source, which I figure probably isn't a good thing.
The amp hums a little, not a lot. I'm pretty confident I followed the ground wiring diagram correctly.
The amp does work, but due to the voltage on the grid, I get crackling and temporary DC offset when I turn the volume pot. Also, voltage is being applied back to my source, which I figure probably isn't a good thing.
The amp hums a little, not a lot. I'm pretty confident I followed the ground wiring diagram correctly.
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