• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

6J1 China preamp thoughts

No it's nothing serious but it's fun to experiment with it. I've just build another one and will try to put passive Baxandal between the two to see if it has enough gain for at least 1:1 output with it.
HI 6v6 Dude.
I am in the process of completing my first kit as my first entry to DIY vavle hifi (with nice power levels that dont bite ) If I read correctly, your post suggests to take two kits... and 2 is twice as good as one?????? Would this mean each kit would essentially be a single channel preamp and combined to be a stereo pre amp?

Cheers
TN
 
99% reduction in hum with just 2 wires and 3 cuts that separate the filament supply ground from audio ground.

ejjS0Se.png
 
I purchased four kits supplied with Chinese 6J1P tubes . The tubes supplied , upon inspection , appear to be a mixture of pulls and used . Bent pins and pin scrapes too which are clear sign of use . Only four out of the 8 tested acceptably . One had inter-electrode shorts , 4 had heater to cathode insulation issues (two tested acceptably after a burn in at 10 volts) . One had low emission . So it's no wonder why so many stuff GE Mullard etc in these cheap kits and boxes and get instant better results

316a
 
I've had one of these for a while now but cast it aside because it sounded pretty bad so I'm happy to have stumbled upon this thread!

3 questions if I may:

Which of the 2 mods are most effective in terms of hum removal (or are they much of a muchness)?

The first mod has an external switch added - what is its purpose?

What power rating does this preamp require?

Thanks!


:Pawprint:
 
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I’ve one I use everyday - I modified it into a follower though. I can post pics when I get home. It was actually a pretty straightforward mod n the end and a good fun to $$ project. I didn’t have any hum issues at all though - so the heater circuit has been left as is for me.
 
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I actually bought another two, with a view to trying a few extra mods like boosting the ac voltage, dropping in a 12V regulator on the heater, and popping a current source in instead of the resistor loading the tube.

No real reason to mind, just thought I'd give it a try and see if it sounds different, or measures differently.
 
Any noticed improvement with the 2 extra preamp ?

Little bit off context but where can I purchase these nice copper rings around the tubes ?

I don’t even know how it’s called so I can do a proper search on e-pay...

Thanks in advance
Eric
 

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Another 6j1

I recently got this pre amp.
But on connecting in the chain there is a constant noise even at nil volume level from speakers.. noise sounds like radio turned on at high volume but without anything being played.

Unit comes with a dc wall socket- could this be power supply issue or the tubes issue!?

Pic of the board:
IMG_20190120_112600.jpg

If it's to do with tubes then planning to get GE substitute and for powerfully issue, i have R core with regulated dc power supply which might need tweaking for that 12 volt input (at present output is at 15volts)
 
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Mods 6J1

And there you go! Grid referenced to gnd and not -ve, as is the output node, plate load is gone, and the cathode load is now 4K7.

Works fine, and I really should have a play with some of the others. :)
 

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Any noticed improvement with the 2 extra preamp ?

Little bit off context but where can I purchase these nice copper rings around the tubes ?

I don’t even know how it’s called so I can do a proper search on e-pay...

Thanks in advance
Eric

Guys if anyopne wants one of these i have one of these new never used that i have no use for. i can send it to you shipped for 22 bucks shipping included or i can also add a pair of real new in box NOS GE jan 5654W for 30 bucks. I have no use for it and i bought for 32.5 bucks.