Tech Tips Tuesday #1 Calculating Preamp Load Lines
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- Опубліковано 15 вер 2024
- In the first video in a new series I cover how to calculate Preamp Tube Load Lines. This comes Straight form a book I've read and love, by Merlin Blencowe. Go check it out, you'll learn a ton: www.valvewizard.co.uk
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Please watch: "Marshall Dual Video 8"
• Marshall Dual Video 8
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Great Video, I have been reading the blog off "The Valve Wizard", which has been very useful, however, this consolidates everything. Thanks John
You're welcome. Glad it helped
Very clear, please more. I shall go through all your video🎉🎉🎉Thank you very much🎉🎉🎉
Great instructional video! I have one of Melvin's books and it is a fantastic source of information on tubes!
Thanks, I tried. Hehe
Sweet now I can try this on a scaled down 4x6v6 twin clone I made when I didn't quite understand all of this. It was a fun project that works, but it could benefit from having this done stage by stage in it to see where everything is really operating. Great explanation and why the endpoints are chosen as they are.
Glad it helped!
Thanks for this presentation. The sine wave sketched in finally clicked this concept into place for me. I have read Blencowe's books over and over and many other texts too. I always lost the plot when it came to visualising the voltage swing. Now it seems so obvious!
Glad it helped, yeah it almost seemed to make even more sense to me while I did the video, sometimes that kind of thing becomes so esoteric, that it's hard to visualize inside your head, but doing it in front of you makes it more clear :D
Great video, keep'em coming! Looking forward for more content from you!
+andrás schóber thanks, glad it makes sense hehe
Ha! Funny, I'm learning this stuff the same way. I just built a fender champ and am plotting load lines and such for the stock circuit to understand why they chose the various resistor values they did. Thanks for the suggestion on the book/site.
Your very welcome :)
Gah phone auto correct YOU'RE :D
MANY Thanks.
You're welcome
Hi, great video. Quick clarifying question; how do you choose the -0.5 to - 1.5 vs -1.0 to -2.0 values? Im confused what those numbers refer to. Thanks, keep up the good work!!
That's the tube grid bias voltage. You select all of the parameters based off the optimal region for your use. Read more here robrobinette.com/Drawing_Tube_Load_Lines.htm
@@FrenchieFilms how did you get 2 grid voltages...is it both sides of the tube, mines 1.5 for each so just a 1.00ma horizontal line
@@riley0187 For preamp tubes, like the 12A*7 types they have two grids because they have two triodes (dual triode). In some cases you may want to bias one half differently from the other.
hi sir i saw your video..you are very professional...sir i have a problem with 6080 vacuum tube..i have a adaptor with 230volt on output and i need 170volt on the anod 6080 vacuum tube how i must calculat anod resistor??? and i want to know the anod resistor will change wich one of (current or voltage anod)???? pleas lead me thankyou
Calculating anode resistance is related to the operating point of the tube not the voltage you're trying to drop. You first need to get the voltage to the level you need before the anode resistor. This is a bit too complex of a solution to explain in UA-cam chat.
again hi sir...i designed my circuit and i want send it for you so pleas make me better guidance ...but on the youtube i cant send it my schematic design...i have instagram and whats app and email addres ...when you receive my message..send me a message please, until give you my email addres or instagram or anything else ..so i talk to you more comfortable ...and thankyou
you can send me email to pdavis at frenchiefilms dot com.
hi sir i want apologise of you because i saw your email very late and i want appreciate to you because you answer my question and you give me your email ...and i will send my schemati circuit for you when i come back home....and again 1billion time thanks
Good video, thanks! Well timed too - I'm working on a new amp build and for the first time am kind of straying away from just copying a known circuit. I have some 6AU6 tubes laying around from a Hammond organ tear down and want to use one as a preamp tube. It is starting to piece together a bit for me. I'm working off this tube data sheet - frank.pocnet.net/sheets/093/6/6AU6A.pdf. Some questions:
I think I'm good on my plate voltage which would set the X axis on the load line.
Can you clarify how you set the Y axis plate current? Say my plate voltage is also 250vdc. I don't know what my plate resistor should be. Do I just need to look for a known working 6AU6 preamp circuit and use that as a starting point?
Second I'd be interested in knowing more about what kinds of design choices you'd make based on tone? You touched on it a bit, but I'm thinking about 'I want my amp to sound like X - what kind of load line do I want to achieve that'.
The current is calculated based on the 'resistance' of the specific spot. You just pick the two easiest to calculate, and it works, the two places are pretty unlikely to happen, but they're at 0V and your max voltage. If it's dropping all the voltage over the tube it's at max current, which is equal to the voltage (250) divided by the anode/plate resistor per ohms law, the other is when the tube doesn't drop any voltage so it's still at max voltage and 0 current which is 250V/ 0 resistance or 0, so your X point there is 250,0, then draw that line between the points. As far as plate resistor, the tube chart you reference shows some examples, for 300V, it shows three different plate resistors you can try (Rp) .1M or 100k, .25M or 250k, and .51M or 510k, It shows a few cathode values as well (Rk) then shows the expected voltage output (Eo). you could try any of those, and just see how it sounds, or try to adjust those values at the voltage you're expecting, which is a bit lower (250 vs 300). As far as the impact it, makes the gain go up or down, depending on how much voltage sweep is accessible on the graph, and it also can compress one side of the signal more, or less, depending on how much head room you give the signal as well. It doesn't change the 'tone' a ton, that's more the coupling capacitors and tone stack etc, but each tube does have a bit of it's own 'color' as well. If you bias towards more gain, it will be crunchier, but have a bit more noise, but for guitars that's not a big deal usually as those can be even better. The only way to know, though, is to tweak and see. If you're going for that Dumble sound he' tended to like cleaner gain stages with more headroom and used local negative feedback to remove noise/distortion. If you want a more crunchy tone, you need to bias more towards that higher output, but expect a bit more noise, or just add additional gain stages, it's a bit tricky and a definite balancing act.
Thanks!
music-electronics-forum.com/t4968/
Thanks for that - I actually read through that thread in depth in preparation for my build. Very good stuff there.