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6J1 China preamp thoughts
6J1 China preamp thoughts
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Old 11th July 2017, 12:02 PM   #1
6V6dude is offline 6V6dude  Australia
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Default 6J1 China preamp thoughts

I normally build high voltage tube preamps but couldn't resist trying the China 6J1 kit even tho I didn't expect much at all. There are few versions, I got the blue one in the pic here. I must say I'm quiet impressed with the sound, it is very clean, no top end loss (that I can hear), smooths out audio little (for a single stage) and can double the output so it's more than a buffer. It is useful little preamp.
But I'm running it at 16V because that's all I had and on the back of the board is printed plate Voltage 28V. I'm reading 38V. Either they made a mistake or maybe it sounds good because it's getting more Voltage. Yes I did drop the heater Voltage resistor to 6.3. Anyone build this thing? What plate Voltage do you get at 12V and what are general thoughts on these 6J1 buffers?
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Last edited by 6V6dude; 11th July 2017 at 12:05 PM.
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Old 12th July 2017, 06:05 AM   #2
azazello is offline azazello  Bulgaria
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Hi, low voltage mode is not very good, better use PCB 6J1 with +B 250 V. I tried variant 6J1 Valve Pre-amp Dual Channel Tube Preamp Preamplifier Board / PCB new hot | eBay with very good sounding. I put 6J1 in pentode mode /You can use triod mode, but mu is about 40-50/ for preamp before phase splitter for PP KT88. I put also 6J5 without changes instead 6J1 with better result
I also used for preamp ECC88 stereo tube preamplifier with power supply PCB DIY
and SRPP Vacuum Tube SRPP Headphone Amplifier Pre-amplifier AMP Board PCB for 6N11/6DJ8 | eBay
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Projects: SE GK71, SE 12BQ6, PP KT88, OTL-OCL 6AS7 Gen. Electric, SEs 2A3 RCA, 300B JJ, 6S4S, 4P1L, EL11 Telefunken, 6AS7 RCA, 6S33S, 6S41S, 6S19P, E84L Siemens, E236L Telefunken, headphone ampl. OTL Loftin White 6AS7 RCA,...

Last edited by azazello; 12th July 2017 at 06:08 AM.
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Old 12th July 2017, 06:33 AM   #3
rotaspec is offline rotaspec  New Zealand
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These low voltage tube boards from China often use a voltage doubler to get the plate voltage.
I wouldn't be concerned with your plate voltage, but do check the voltage ratings of the electrolytics to make sure you are not about to fry them.
Of course, if the are any opamps in there, you better check the voltage rails on those as well.
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Old 12th July 2017, 06:40 AM   #4
azazello is offline azazello  Bulgaria
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PP KT 88 with preamp 6J1 Valve Pre-amp Dual Channel Tube Preamp Preamplifier Board / PCB new hot | eBay I used 6J5 instead 6J1 /the front two tubes/.
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File Type: jpg PPKT88-1.jpg (328.6 KB, 1795 views)
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Projects: SE GK71, SE 12BQ6, PP KT88, OTL-OCL 6AS7 Gen. Electric, SEs 2A3 RCA, 300B JJ, 6S4S, 4P1L, EL11 Telefunken, 6AS7 RCA, 6S33S, 6S41S, 6S19P, E84L Siemens, E236L Telefunken, headphone ampl. OTL Loftin White 6AS7 RCA,...
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Old 12th July 2017, 05:18 PM   #5
azazello is offline azazello  Bulgaria
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Good deal: Tube 12AX7 12AU7 Buffer Audio Preamplifier Pre-AMP AMP DIY PCB bare board | eBay
I changed 12AX7 to 12AT7 for better sounding. PCB can drive SE 2A3, 300B, 6AS7, 6S33S, 6S41S...and disconnected FB /R4/, that decrease sound quality, R5 to ground.
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Projects: SE GK71, SE 12BQ6, PP KT88, OTL-OCL 6AS7 Gen. Electric, SEs 2A3 RCA, 300B JJ, 6S4S, 4P1L, EL11 Telefunken, 6AS7 RCA, 6S33S, 6S41S, 6S19P, E84L Siemens, E236L Telefunken, headphone ampl. OTL Loftin White 6AS7 RCA,...

Last edited by azazello; 12th July 2017 at 05:25 PM.
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Old 16th July 2017, 04:56 AM   #6
6V6dude is offline 6V6dude  Australia
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Quote:
Originally Posted by rotaspec View Post
These low voltage tube boards from China often use a voltage doubler
It does have voltage tippler, those two transistors take care of that. Other than than it is a straight tube signal. I'm getting another kit just to see what I can do connecting them in serial or chaining all 4 tubes. Depending on total gain and the noise levels it might be useful for mixer, adding tone control, etc.
Other than that I can't see any radical mods being done on the board it's self, it's double sided so I'll explore what can be done with it as it is.
I'm using this one for recording music off the Net, it helps to smooth out some of the grittiness of mp3 broadcasts, it also makes great level control that's why I thought of a mixer. It's interesting fun anyway, for the price one can't go wrong.
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Old 16th July 2017, 06:30 AM   #7
auriga2001in is offline auriga2001in  India
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I have a variant board that sounds good, but hums a lot. I tried adding filter capacitors, but it didn't help.
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Old 19th July 2017, 02:54 AM   #8
6V6dude is offline 6V6dude  Australia
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Quote:
Originally Posted by auriga2001in View Post
I have a variant board that sounds good, but hums a lot. I tried adding filter capacitors, but it didn't help.
This board is quiet. But try another power supply, some can be noisy.
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Old 20th July 2017, 09:07 PM   #9
audiowize is offline audiowize  United States
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It's also important to mention that there are tons and tons of low voltage Chinese tube preamp PCB's that ignore the issue of grid current at such low plate voltages, and they may specify a 100K input impedance, but with the actual triode factored in, this is usually much lower.
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Old 20th July 2017, 10:10 PM   #10
Hedliden66 is offline Hedliden66  Sweden
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Mine is waiting for a box. Had to rearrange a bit, so all of the tubes will be visable. It's a fun volume regulator for me, nothing more nothing less, so to speak
6J1 China preamp thoughts-6j1preamp-jpg
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