Howdy. Great. The cathode line was new to me. Credit shall go where it is due for taking the time and making the effort to make the video. Regards.

Great video, thanks for your work. The visual on the scope really helps you see what's actually happening to the wave.

Thanks Jason, more great information, carefully explained as always.

@HeadfirstAmps

2 жыл бұрын

Glad it was helpful!

Subscribed , load lines have been mysterious graphs for me for years, finally some one explained it in a way I can understand. Thank you for making this video.

@HeadfirstAmps

Жыл бұрын

You’re welcome!

great video. Thanks for slowly stepping through this,- very interesting

Very good content, thanks! I did some preamp tunning on my mesaboogie .50 + e other bootique amp with very good results, to archive the preamp drive sound I had in mind. Preamp cathode resistors are very important to the final tunning of the amp.

Thanks Jason! Another great explanation video.

Very cool vid mate, super informative.

Greatings from the UK! Just discovered your channel today!! Subscribed straight away!! Bloody marvelous videos!!!

@HeadfirstAmps

2 жыл бұрын

Welcome!

Thank you. This is difficult to explain to another. I knew this from High School and College and technical experience building guitar amplifiers. So I get everything you spoke of. Still, I admire your effort to take this explanation on for your viewers.

Outstanding video. We’ve all heard asymmetrical clipping in our pedals through the years and it is an interesting sound. By my figuring, the waveform is a mixed one, a bit more complex dynamically than the traditional mostly symmetrical one. There is clean tone mixed in and it sounds like brilliance. I’m going to try this on my 1970 #1987 50W head to see if I like it. I already love the amp’s sound but this will be a simple mod to make variable. Thanks for all the gain charting. That’s a lot of time spent. I’ll report back.

Merlin's site and books are GREAT!

@zabtej1645

5 күн бұрын

what is the site again?

Thanks for that Jason, fantastic explanation 👍. Catch up soon bro

@HeadfirstAmps

2 жыл бұрын

Hey Chris, thanks man. For sure, would be great to catch up mate.

Awesome video! :) Thanks man!

Very helpful, thank you!

@HeadfirstAmps

2 жыл бұрын

No worries!

THANK YOU FOR THIS VIDEO >>>>> I just started digging into trying to understand this better today and then what do I see on KZread? Funny how things align sometimes... I have tinkered with the MC2's preamp stage the other day but I tried to cut the bass out from the first and second stage... Somewhere during all this I lost the function of my fx loop switch and my lead volume quit working... it was just on all the time and the gain only worked kinda as a volume and gain combo.... lol. Something was goofy from the get go though when I built the amp. THe rhythm cahnnel is TOO dark and the bright pot doesnt work at all to change it. Gotta look it over YET AGAIN!!! but its all good and fun as far as im concerned. Frustrating at times but worth it.

Hi Jason, I love your channel and enjoyed this video along with your plate resistor video. Your explanations are clear and easy to understand. Could you enlighten me as to when to use audio or linear pots? I see variations on different amps and would like to understand why? Thank you for your time.

@HeadfirstAmps

2 жыл бұрын

Glad it was helpful! Normally audio is used when the pot is functioning directly as a gain or volume adjustment. It's audio, meaning logarithmic, which matches the db scale so it sounds more natural as a volume adjustment to our ears. Linear would then be used to where the circuit is calling for a more even adjustment through the range, that is typically not amplitude (i.e. gain or volume) related.

Tanks, Jason, for the awesome stuff you do! You could/should start holding online classes.

@HeadfirstAmps

2 жыл бұрын

Maybe a live Q&A?

@ioncewas

2 жыл бұрын

@@HeadfirstAmps Or a whole frickin syllabus on building amps and being badass! But yeah, a live stream would be cool. Or an AMA over at reddit.

ha, just had 'Designing Preamps' out yesterday to look something up.

So funny - I just learned to draw load lines and was watching and realized Jason didnt add the cathode resistance to the load resistor value when determining current. I thought for a moment there were other ways to do it. Then as I am watching, the ticker came across the bottom saying to add the csthode resistor value. Whewwww.

What awesome work you've done on this educational series of videos, so thank you! Now, I have a question about the cathode follower resistor that is typically 100k. I know from the ampbooks calculator that using a 68k there (left over from trying some previous mods) will slightly lower the impedance seen by the tone stack, and a slightly larger cap is needed to attenuate the right frequencies for the JEL mods, but do you know of any other affects that using a 68k there would have on the preamp's performance in theory or otherwise?

@HeadfirstAmps

Жыл бұрын

I think Merlin covers this in his wonderful book, I might find time to look it up.

can you make a video that show us individually all gain stages, phase inverter and power tube clipping? I would love to see how one side of the PI clipps and how a power tube clips :) and how PI and Power tubes clip in conjunction (how it diferes from preamp tubes)

@HeadfirstAmps

2 жыл бұрын

Sure, sounds like a good topic! Plexi style.

Hi Jason wonder if you could do a video of using a isolation transformer when working on vacuum tube amps with oscilloscope

Awesome video Jason. They ALL are man !!! The more I watch the more I want to try my own mods. For instance, ... I have the SC20H matched with a 2x12 with Vintage 30's. Very articulate and super distinguishable insofar as, you can hear each and every note that gets picked, even under full gain. Great setup !!! However, ....... It is soooooo BRIGHT that it is really almost unbearable. I hear you talking about "arresting" the bass frequencies going into the preamp section, on a lot of your videos. I seem to have the polar opposite situation. There's wayyyyy too much Treble in the amp - overall. To the point that I have the treble pot on absolute 0 and use the Presence for the high end. Does this sound familiar to you regarding the SC20H?? If I could "correct" that I would be a super happy camper. Any ideas would be greatly appreciated. I have not performed any mods to any of my amps before, but have been inside a multitude of many different models. Thanks for sharing your knowledge with us. Super cool stuff man !! - Cheers !!

@HeadfirstAmps

2 жыл бұрын

Hey man, great to hear you are digging the clips. Here's my suggestion: put a 470pF ceramic or mica across (in parallel with) the 100k resistor that goes from V2b to ground, i.e the cathode follower

@lechstryzewski9350

2 жыл бұрын

​@@HeadfirstAmps I will definitely do that and see what I get. Thanks for the quick response !! - I will let you know how it turns out. Then, I will research understanding it more - LOL - Thanks again for the suggestion Jason.

@kowpow2259

2 жыл бұрын

I've got the same amp and did this mod. But here's the secret. Shhhh. Try a different speaker. No really! A pair of G12T-75.

Do you think asymmetrical clipping in the power amp sections valves (caused by slight phase inverter imbalances) could be reflected in the negative feedback sent to the preamp, and actually shape the distortion of the preamp? It’d be a tough one to test without an attenuator because even a 50w is ear bleedingly loud by the time you hit power valve distortion, but it’d be interesting to see if it does.

Thank you Jason. Your recording tone is great. May I know how you record the amp? via reactive load and mic up with real cab?

@HeadfirstAmps

2 жыл бұрын

Mostly with a reactive load, sometimes a 57 on my old GB loaded Marshall 4 x 12

It's worth looking at an unbypassed Cathode resistor as what is referred to as degeneration. This is local negative feedback and actually tries to linearise the stage - all other things being equal. The interesting thing about the so called ''çold clipper' stage (IMV not the right name for it) is that the 10k R being so large, reduces the gain and tries to reduce the distortion of the stage (by large degeneration)- BUT because the stage is so far off 'centre bias' due to the very low current it overloads very asymmetrically. We all tune these things by ear, like baking a cake, but it's an interesting rabbit hole understanding objectively what is actually going on.

Great as ever sin city song by acdc 🤘🏻🤘🏻🤘🏻😎

Hey brother ive got a, well, a statement and a ? In one 😂 i learned this after plate loading/4 staging my old 800 2204. This thing is a beast in terms of clip but not the fizzy shit u get from Jose style stuff. I found that by shorting, bypassing, whatever, the 1st, 2nd and 4th cathodes with caps the amp became whisper quiet. No cross talk no oscillations just extremely quiet. Im talking 1st stage 100nf/6.8k, 2nd 470nf/4.7k, 3rd 2.2k and 4th 1uf/1.5k with 6550s at maybe 55mah which i would say is just asking for trouble. When i started all cathodes were unbypassed and it was noisey. You ever notice a reduction in noise by simply bypassing cathode resistors?

What I struggle with in understanding this is the difference in tone between symmetric and asymmetric clipping. Symmetric clipping is all odd-order harmonics, and I get that those will have more dissonance with the fundamental and string overtones which are even. And I get that asymmetric has both odd and even order harmonics. What's confusing is will that asymmetric clipping sound more pleasing because it has some even order harmonics, or will it sound more aggressive because it is more complex, having both even and odd order harmonics? Then what's the effect of clipping that cathode follower going into the tone controls? Is that making the overall clipping back to more symmetric and its the combination of the two that establishes the amount of saturation and overtones?

So when you draw a cathode load line does it mean you have the start the end of it from 0v the continue the line until it intersects the plate load line?

Diamonds....and dust...

Very good stuff bro. I have a question.what the small resistor value I can use on 12ax7 cathode ?plate resistor 100 k. Thanks.

@HeadfirstAmps

2 жыл бұрын

820 ohm is probably the lowest you’ll find in a guitar amp. Amy lower and you’ll be slamming up against the saturation cutoff.

@bepeboy444

2 жыл бұрын

@@HeadfirstAmps Thank you for answer me bro. Stay well!

i have some switches setup (2204 build). One switch changes the V1b cathode resistor from 10k to 2.7k. The other switch adds a .22uf cap. When the cap is engaged i cannot hear much difference when switching between 10k and 2.7k. Also i have tried many caps and have found the small 50v polyester box caps have the lowest noise.

@HeadfirstAmps

2 жыл бұрын

Hey John. Yeah the bypass will equalise the amount of gain, however you should still find that the 10k retains that Cole clipper 'graininess' to the tone.

@johnmiller9219

2 жыл бұрын

@@HeadfirstAmps yes the 10k with the cap to me sounds the same as the 2.7k with the cap. The 2.7k alone has more gain than the 10k

Hey Jason do you remember what clipping mode you used in the playout?

@HeadfirstAmps

2 жыл бұрын

Sure, that’s the Shirley in the 10k gain structure switch pos with my high voltage FET boost on in the front end. No clipping diodes in this amp.

On the cascaded preamp stages, is it better to have the first stage with the 2.7K, 0.68mf and the second stage 820, 330mf or the reverse?

@rdavid3848

3 ай бұрын

Yes, there is a difference, which comes first. It is smoother to cascade starting with less bass frequencies like you suggest and then larger frequencies after.

How was I not subscribed?! Unacceptable.

@HeadfirstAmps

2 жыл бұрын

welcome aboard!

So, is this also called "starving the plate voltage?" I've always heard that term in amp modding discussions but never really knew what the techs were talking about.

I have a Friedman pt20 and it has the 3 way toggle switch on it for different gain stages and I was wondering if there was a way to make that foot switchable?

@HeadfirstAmps

2 жыл бұрын

Its possible, but requires a few relays and a mute circuit. Changing the cathode generates a large pop as the DC bias changes.

@erpringle

2 жыл бұрын

@@HeadfirstAmps Thanks for the quick response, I asked Dave Friedman if he could do it and he said he couldn't. I think he just didn't want to mess with it. I think it would be a good addition to the pink taco or any other amp with the gain stage toggle switch. It could replace an overdrive pedal or be like having another channel or two but I don't think I will tackle it as I wouldn't know where to start. Great video, thanks for the info.

@HeadfirstAmps

2 жыл бұрын

Its a big job to retrofit to an existing amp, so I can totally understand where Dave is coming from. You'd need to design it in from the outset.

@erpringle

2 жыл бұрын

@@HeadfirstAmps yeah, not worth the hassle but it would be cool. I have the origin 20 also and was thinking about trying one of your mods on it as it is a fairly small investment if I screw it up. Thanks for all the useful information, you have some killer videos on here.

@HeadfirstAmps

2 жыл бұрын

Thanks Randy, I appreciate the support man.

cathode resistor in series with a cap to ground. what does this accomplish? (bogner ecstacy R12 mod). also, how can this be tweaked for different results?

@HeadfirstAmps

11 ай бұрын

A resistor in series with a cathode bypass cap is simply limiting how much impact the bypass cap has.

@geezberry8889

11 ай бұрын

@@HeadfirstAmps thanks!

The supply voltage on the Node is so low compared to a JCM800! a JCM800 has around 330v

@HeadfirstAmps

2 жыл бұрын

Well, it depends on what era 2204 you are comparing to. I can think of 3 variations all with different node voltages.