Tube Lab

[@brucecollins6435]

Much better Jim! Bruce @ Mission Amps

[@elementalwattson]

Hi! Very good explanation! I have a question: How can I add a Line Out jack to this preamp?

[@tubelab194]

@@elementalwattson hmmm, the schematic clearly shows a RCA out, which is of course your Line or Signal out. Or am I not understanding what you are looking for? A much updated FREE schematic of what became our best selling Kit (Universal 6or12SN7 Preamp v3.0) is available on our website under information downloads. Here's a Link: valvesnmore.com/?page_id=11919

[@dmark2639]

Thanks for explaining this preamp circuit. I will be looking at your power supply video next. Wouod this design be suitable for a headphone amplifier? Im guessing i would have to add a power tube after this preamp circuit?

[@tubelab194]

Hi @dmark2639 thanks for checking out our videos! Yes you would need a power tube after the preamp circuit. You should take a look at our most recent videos where we show off the prototype of our new integrated headphone amplifier. It's not using the same preamp circuit as our Universal and E80cc designs, but something new specifically designed to get us some more power output. Happy to answer any other questions you have, cheers!

[@dmark2639]

@@tubelab194 Thanks, I watched all your headphone amp videos last night. I'm excited to how it turns out. I like the multi-tap transformer that makes it very versatile with many headphones as well as speakers. I'd love to try a test build!

[@AUDIOETRADIOATUBES]

Very interesting video for beginners

[@JR-Canada]

Thanks Jim!

[@CharlesSelva]

How do I do balanced preamp with this design? Thanks best wishes!

[@tubelab194]

If your signal arrives balanced, and leaves balanced, you basically build two of the circuit. Now remember that's only one channel, so for a stereo preamp you need 4 circuits! Personally I don't think balanced circuits have any place in home audio, it was developed for professional use and that's were it does help reduce noise for very long cable runs.

[@Torpengpogi]

hello mr jim, i have a few questions hope you can answer, thanks. 1) can i increase use B+ more than 250V, let's say 300-350V? for the 6SN7? 2) can i increase the input coupling caps to 0.22-0,47uF? 3) what is the gain of this design circuit? 4) can i add a grid stopper resistor on both pin 1 and pin 4 inputs? 5) what is the tube rectifier that you can recommend for this circuit? 6) is it ok to put another volume control on the output in addition to the input? 7) why there's no coupling caps and grid leak resistor between pin 2 and pin 4? thank you and more power to you - from Toronto

[@tubelab194]

This was a prototype build, using a direct coupled interstage (no coupling capacitor), it only worked well with certain heavy duty mil spec 6or12sn7 tubes, other regular types got noisy. What I'd recommend is go into the store www.valvesnmore.com to information and you will find a totally revised Universal 6or12sn7 Kit Preamp schematic. You can buy a full or light kit or just borrow the schematic and build with your own components.

[@Torpengpogi]

@@tubelab194 thanks jim for the quick reply, and i just checked your website and explored the latest revision of this 6sn7 preamp. but i have one last question : is there a possibility that i can make the output a balance output to drive my cx400 analog electronic crossover without using a direct box, a separate balance output, other than the unbalanced rca out? just in case i order this full kit in the near future, thanks again.

[@tubelab194]

@@Torpengpogi no all of my Kit Amps are SE (single ended) designs. To obtain a balanced (XLR) output, you would need a phase splitting stage. The 12au7 would probably do the trick, one for each channel. In a future Tube Lab, I'm going to talk about SE vs Balanced. As an audiophile and minimalist, I'm strongly on the side of keeping the signal whole (SE) from beginning to end. Yes recording studio make extensive use of XLR cables, but that makes sense, long runs can lead to a lot of noise. At home we run cables for very short distances, so have no need for the noise cancelling qualities of a balanced signal.

[@JR-Canada]

Are 6N8 specs equal to classic 6sn7 or 6SN7GT??

[@tubelab194]

Good question! As far as I know the Russian 6N8S, does not have a distinguishing number for earlier 6sn7gt equivalent and later GTA and GTB equivalents. I just checked my inventory and tubes from 50's and 60's are marked the same. It only makes sense that the early Russian 6N8S tubes are rated as 6SN7GT, given that I believe they are either copies or made under license. And the later ones are either GTA or GTB's (identical tube spec except heater spec). So what to do? The Russian tubes almost always have a date code, so a tube made before 1963 most likely is a GT and after GTA or B. I stand to be corrected on this! Note other than MELZ machine gun holed plate version from 1950's (v.expensive) they are inexpensive, just run them and see how they do! Many Russian tube types are solidly made and can take some abuse! I stock a good selection of this tube.

[@JR-Canada]

@@tubelab194 thanks for clarifying that. I have a Chinese ( very high quality though) 845 tube amp Dared VP-845 that has 6N8 tubes marked on the heavy solid copper heatsink/top, and It came with Chinese(unmarked) gray metal base tubes 6sn7 I believe... other tubes are 12ax7 telefunkens and shugyang 845M power tubes. So Which do I upgrade those stock 6sn7 to? They are a bit bright... I tried JAN NOS Sylvania 6sn7WGT brown base tubes but they don’t seem to have good highs... base good though. Any advice? I’m in BC btw) AND my speakers are magnepan.7i...

[@tubelab194]

@@JR-Canada Nice amp! Well the 6sn7's are probably in the driver slot, so you want a robust high Gm tube to drive the output Triodes. The selection is huge any quality 6SN7GTA or B would be worth rolling. And because you only need a pair not that expensive. The GE 6SN7GTA or B (my #10 or 138) is a possibility (watch Fridays Tube Lab), I've also got some vintage Tung-Sol's 6SN7GTB (nos) very nice tubes, my inventory #11. And if you wanted to try some fun tubes as well, just put a buy in for some "discount octals" under discount tubes and I'll find some interesting $10 tubes for you to roll!

[@JR-Canada]

@@tubelab194 placed the order today Jim. Thanks)

[@BuBanBan]

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