Tube Preamp Construction Techniques

[@williamli7477]

Wow just discover you channel today ! I keep your RM 9, as it's a fine piece of hifi. Great to see and hear from you directly, and see that you are actually quite young !!

[@PederWeierholt]

you're videos are way better than alot of other videos on the theme, please do not stop making them.

[@carywatmore]

Goodbye Roger, you will live thru your RM-4 and RM-5 and the RAM tubes. RIP 🙏

[@Finom1]

We are looking forward to your next video on "How to make a Two Stage Amplifier". Thank you for taking time to help me get started so I can better understand and have the confidence to further my education with you.

[@jon_byler]

Thanks for sharing your knowledge. You have a way of explaining things that help it all make sense. I also appreciate your design philosophy and overall lack of quackery. So much B.S. and false information getting spread around by people who don't have a clue.

[@JethroBoDean]

Very very good info I have a number of old tube radios and am trying to learn enough about them to convert them into guitar amplifiers any chance you might have a series on such an undertaking

[@sovietsanta1]

i'm designing a stereo 6sn7 tube preamp for my stereo but i'm stuck on the equation for the coupling capacitor values and the equation for the cathode bypass capacitor values. Do you think you could tell me what they are because they seem extremely hard to find. I did find two of them on one website i think the coupling one that i found is right because i can get the same values as other schematics but the one for the cathode capacitor confuses me and i cant seem to get it to work i hope your able to help thanks.

[@adriensauvaget2058]

Super great videos here Roger, hopefully you'll have some time to do some more !

[@milesfozznick]

Hi, i hope you been doing ok i seen that your last video was some years ago. i'm getting into building tube amps for a business and i already know enough to pop components together from kits and build really good looking cases/chassis for them but i want to learn how to build them from scratch. is there anything you could recommend for a good solid foundation of tools and gadgets to start off with and will be able to keep using as i progress into more complicated stuff. I'd like to start on building mono block preamp style stuff for hifi. at the time i have a cnc shop and a wood work shop and i been dying to get into doing this for a long time and now i have the time to but i have no friends or go to person for lessons on this stuff....and people like you don't come around everyday, in fact its a dying art yet at the same time the demand is vary much still here. anyway would love to hear back from ya.

[@ianhames2465]

You teach very well, makes working on tubes with more confidence. How do you make the RIAA circuit for the MC cart and how should they be placed?

[@nathanpc]

Great to see that you're back on KZbin!

[@MusicReference]

Thanks, I have been busy with getting my audio electronics school started in the San Francisco Bay Area. I will soon have some video up on that.

[@suzanne_atkinson]

this is great, I wish you would keep posting

[@jermcrow3408]

great stuff please keep making videos and thank you for sharing your knowledge with us. thumbs up!!!

[@KirkWagner147]

did you never make the next video in this series ?

[@pablopitola3598]

do you have the power supply schematics?

[@larryshaver3568]

I agree pertaining to building the channels separately then there is no chance of microphonic noise

[@mladenkapisoda9944]

Looking forward to more usefull videos.. Thank you! :-)

[@jordanrenaud-pq7rx]

Interested for certain.Must follow.

[@SkazaTV]

Thank you for cool videos!

[@kokonoraa6138]

Thanks for this, good info

[@jaimieandash9484]

Thank you

[@MusicReference]

@sovietsanta1 use the standard c=1/2piF. www.sengpielaudio.com/calculator-XLC.htm will help. For the coupling cap R is the input resistance of the next stage to ground. Typical values are 0.1 uf and 470K ohms. For the cathode bypass the capacitor is much larger because the resistance is much lower. The resistance there is the cathode resistor in parallel with 1/gm of the tube. Typically this is just a few hundred ohms so the cap is 470 uf. The particular tube does not matter so much but high gm tubes do have lower R and bigger C.

[@sovietsanta1]

thank you its hard to find some of this information

[@gregkrobinson]

sovietsanta1 Ok, sorry, but the info Music Reference has given you is incorrect. To calculate a cathode capacitor, you need to first know your cathode resistor value, and then decide your -3dB point. Say your cathode resistor is 1k, and you decide that you would like your -3dB point to be below audible frequencies, maybe say 5Hz. The formula to calculate the capacitor value is C = 1/(2 x Pi x f x R), with R being the resistor value in ohms, f being your selected -3dB frequency, Pi being 3.14..... So in this example, the calculated capacitance is 31.8309uF. A close standard value is 33uF. You can then rearrange the formula to calculate the resulting -3dB point, f = 1/(2 x Pi x C x R), which is 4.8229Hz. I don't know why Music Reference has brought up the cathode resistance in parallel with 1/gm, which is used to calculate the cathode load line and output impedance of the cathode, but has no bearing whatsoever on the selection of a cathode bypass capacitor. If you want to calculate AC coupling capacitor values, the maths becomes a fair bit more complicated, and you should read the Radiotron Designers Handbook or the RCA Receiving Tube Manual if you want the full details, but a very approximate method for calculating them is to look up the plate/anode resistance of the tube at typical operating conditions (if the datasheet has various operating conditions, select the one which most closely matches your circuit). A typical value for a 12AX7 stage is 65k. With this information, you can calculate the output impedance of your triode stage, as the output impedance of the triode is the plate/anode resistance in parallel with the Plate resistor, which might typically be 100k. These values in parallel are ~39k. Now, to calculate the AC coupling capacitor, the formula is as follows: C = 1/(2 x Pi x f x (Zo + Rl)) where Zo is the output impedance that we just estimated, and Rl is the following load resistor. Say for example you choose a -3dB of 50Hz, and the load resistor is 470k, Zo is the 39k we calculated before, then we would calculate the coupling cap to be 6.3 nano Farads (0.0063uF). A close value is 6.8nF, so calculating backwards again, we find out -3dB point to be 45.98Hz. Remember, these are approximate values, if you want more precise results you will need to do quite a lot more math to calculate the operating points of your gain stages.

[@sovietsanta1]

Greg Robinson thanks i shall remember to use this when i start my project back up

[@MusicReference]

Greg Robinson Dear Greg, Since you mention that 1/gm does calculate the impedance at the cathode it is obvious that is the impedance you must bypass. Think of what would happen with a very large cathode resistor like 100 K going to a negative 100 volt supply for 1 ma. Would you use 100 K in your formula or 1/gm? What if the cathode resistor was a current source of infinite impedance?

[@rtybn2012]

Your comment that the wall warts are well regulated is not true at all. They have No regulation circuits inside at all. Take one apart and you see only a transformer, 4 diodes an a single capacitor, nothing else.

[@SarcastSempervirens]

there's literally no techniques here

[@choirudinabdulgani6351]

Made in china the best in money

[@coldfinger459sub0]

I'm in my first electronics class in college and I picked a tube amplifier has my first project to complete class. It would be nice if you did a simple little tube amp project like in your other videos with a little more detail on the exact values of components used. I hope to turn my skills and to be to the level to attend some of the Berkeley classes for hi-fi audio