Awesome video!!! I have been designing Vacuum tube guitar amplifiers for 28 years since getting my Degree in Electronics. I was a guitarist and loved their tone and dynamics there was little academic emphasis on tubes during formal education most of my knowledge I gained searching out "Old Timers" and discovering the Radiotron Designer's Handbook 4th Edition, which I notice you reference is a "Goldmine" It's nice to see somebody knowledgeable! Best Regards
Someone likely mentioned this in the comments already but... faulty old filter capacitors are definitely a source of hum in tube amps and not a rare issue in vintage tube guitar amps.
Nice work, there's multiple things going here, raising the filament supply, adding feedback to V1's cathode which might contain 60hz because of filament raising, and not introducing phase shift with coupling capacitor. Getting out my tattered RDH4 now to see what it says. I'll keep your handy dandy tip ready for future designs. Thanks
Excellent and extremely useful educated info into hum of tube amps. A question please. I have a class A SE UL stereo amp I am designing that has a NFB from speaker 16Ω tap to the 12AX7 preamp cathode. I get a light hum that peaks at 100Hz and 150Hz acoustically analysed. If I input 1000Hz I see the envelope of the output modulated possibly by this hum. If I do your nice advice I will probably have two signals added at the cathode of 12AX7 (one is NFB and the other fro R hum resistor). Will that work? I will certainly try but is it possible?
Very nice idea. I will give it a shot. From what I can see from your schematic is coming off V1 cathode, use a 470K to the cathode of V2, or power tube. Is this correct? Would like to see the waveform after the resistor is added. Thanks much
I have a question. My output tube cathode has the parallel resistor/capacitor, but not the other resistor to the cathode. Can I attach R hum directly to the cathode? Thank you.
The most common solution to that amp is to elevate the heater. There are several schematics online showing how. Basically, it involves connecting the heater centertap to the cathode of the power tubes. That raises the heater centertap to the bias voltage of the power tube and quiets the residual hum.
Would the same steps apply to trying to diagnose 180Hz hum? Not entirely sure where it is coming from, but it is present with all knobs at minimum and nothing plugged in. The hum then increases with the REVERB knob, even with volume at minimum. Interesting. And, it is present even if the reverb tank and footswitch are disconnected entirely. Thoughts? '65 Princeton Reverb clone. Thank you, your channel is very informative!
I believe this would be applied to the output power amp section. I have a hybrid Marshall. A 12AX7 preamp with a solid state output. I'm not quite sure if rewiring the preamp with a triode tube would produce any quantifiable results.
A solid state output has other issues, so this isn't applicable. Also, a triode power tube is much less prone to hum and should not need this neutralizer in most cases.
Great video and tutorial - thank you very much for the information. How would you handle a fixed bias push pull circuit such as a Princeton 6g2 layout? Any suggestions regarding the Inversion and injection point into the 2 power tubes?
Thanks for watching. It is a solution for single-ended amps only. Because: Rule 1: PP configurations are hum canceling circuits. Rule 2: The PP tubes have grounded cathodes, which makes the PP configuration absolutely & positively deathly quiet. If not, then 1) one or both of the tubes is/are getting old, 2) the power filter caps on the 5Y3 are suspect or 3) the preamp tubes are the problem: old tubes or the connection to the input jack is creating a hum (ground loop issue).
HI, I am going to try the 20k pot today. I just wanted to clear up something first, If you have time. I did not have a center tap on my 6.3 v secondary and used the 2 x100ohm to create one. This center tap lead would then go to the wiper on the pot and the 1 and 3 would go to the respective V1 and V2 cathodes directly on the tube pins. Correct?
Great Video. I've ben using similar cicuits for years. In some amps I can even get a boost on some frequencies... Funny how most well know Amp Mod Guru's don't know anything about Noise Canceling Inverting Loops. These work well and you don't need to add a big cap.
I will share some general information because I don't have a photo of you chassis. If you still have hum, the top issue is generally wiring. The wiring must be absolutely neat. If you look at a Fender Deluxe, you will notice all the wires are no longer than required to connect between 2 points. There must be NO EXCESS wire. Excess wire acts like an antenna to pick up noise from the B+ or Heater wires. All the wiring needs to be laid flat against the metal chassis so the chassis can absorb and ground out any interference that is causing the hum. If a wire needs to cross another wire it must cross at a 90 degree angle. Also, do not run any wire along the side of a component (cap, resistor, etc.) Wire must cross over the component at a right angle or not at all. Wiring at a socket or a pot is a challenge because that last inch at the lugs requires running wires in parallel. (UGH), but just 1/8 inch of separation can make the world of difference. Tube amp wiring is challenging.
Hi, very interesting technique. I wonder why does V2 has two resistors, is to implement correctly? because usually there is only one resistor with a capacitor. Secondly, does it need the filter capacitor on the cathode resistor or it will still work without the capacitor? Thank you
On the cathode: one resistor is 1 ohm to take a direct measurement of the current the other sets the bias. The cathode does not need a bypass capacitor for this to work.
I had this question sent to me last week and I have had time to think about it more. I really wouldn't suggest doing this with power tubes of a AB amplifier. The cathode will need to elevated and the RC filter needs to be rated for 7 watts. However, it can be done. The cathode of the power tube needs to be elevated to 2VDC to 5VDC and a resistor (10W rated) connected from the cathode to the output of the preamp (generally the second stage). It is the preamp that is normally the source of the hum that needs corrected. So... What would be better is to elevate the ground on the preamp section. Connect the centertap of the 6.3VAC filiment to the RC filter of the preamp second stage (it is normally at 1VDC). Then connect a resistor from there to the cathode of the first stage of the preamp.
No, you cannot hook your PC to an amp or any other high voltage device. It will require an interface that will isolate your pc from the devices (like the amp or speaker). The isolation devices will output safe voltage levels for the pc (under 5 volts). I have no recommendations for you. I use an oscilloscope that has outputs to send to a pc to safely acquire data.
Awesome video!!! I have been designing Vacuum tube guitar amplifiers for 28 years since getting my Degree in Electronics. I was a guitarist and loved their tone and dynamics there was little academic emphasis on tubes during formal education most of my knowledge I gained searching out "Old Timers" and discovering the Radiotron Designer's Handbook 4th Edition, which I notice you reference is a "Goldmine" It's nice to see somebody knowledgeable! Best Regards
Someone likely mentioned this in the comments already but... faulty old filter capacitors are definitely a source of hum in tube amps and not a rare issue in vintage tube guitar amps.
Now here's some good usable knowledge thank you Jim !
Nice work, there's multiple things going here, raising the filament supply, adding feedback to V1's cathode which might contain 60hz because of filament raising, and not introducing phase shift with coupling capacitor. Getting out my tattered RDH4 now to see what it says. I'll keep your handy dandy tip ready for future designs. Thanks
Putting a 12.6vdc regulated heater circuit would also help also. At least on the preamp section. Power tubes 6.3vac no problem since they cancel out.
Excellent and extremely useful educated info into hum of tube amps. A question please. I have a class A SE UL stereo amp I am designing that has a NFB from speaker 16Ω tap to the 12AX7 preamp cathode. I get a light hum that peaks at 100Hz and 150Hz acoustically analysed. If I input 1000Hz I see the envelope of the output modulated possibly by this hum. If I do your nice advice I will probably have two signals added at the cathode of 12AX7 (one is NFB and the other fro R hum resistor). Will that work? I will certainly try but is it possible?
Thank you for explaining how get rid hum, in my ferrograph series 4 valve reel to reel tape recorder
bless you mr whiteside
Very nice idea. I will give it a shot. From what I can see from your schematic is coming off V1 cathode, use a 470K to the cathode of V2, or power tube. Is this correct?
Would like to see the waveform after the resistor is added.
Thanks much
Even if there is a voltage rise on V1 cathode this could be adjusted back down with resistor value changes on the V1 cathode and or plate resistor.
I have a question. My output tube cathode has the parallel resistor/capacitor, but not the other resistor to the cathode. Can I attach R hum directly to the cathode? Thank you.
Great info! Thanks for doing the video!!
Excellent video. Could you please explain how to get rid of hum on the Marshall 18 watt lite amp from preamp? Thanks .
The most common solution to that amp is to elevate the heater. There are several schematics online showing how. Basically, it involves connecting the heater centertap to the cathode of the power tubes. That raises the heater centertap to the bias voltage of the power tube and quiets the residual hum.
Would the same steps apply to trying to diagnose 180Hz hum? Not entirely sure where it is coming from, but it is present with all knobs at minimum and nothing plugged in. The hum then increases with the REVERB knob, even with volume at minimum. Interesting. And, it is present even if the reverb tank and footswitch are disconnected entirely. Thoughts? '65 Princeton Reverb clone. Thank you, your channel is very informative!
Please send me an email (see my RUclips channel). I am going to need some more information and maybe a sound clip for analysis.
I believe this would be applied to the output power amp section. I have a hybrid Marshall. A 12AX7 preamp with a solid state output. I'm not quite sure if rewiring the preamp with a triode tube would produce any quantifiable results.
A solid state output has other issues, so this isn't applicable. Also, a triode power tube is much less prone to hum and should not need this neutralizer in most cases.
If we apply dc voltage to heaters ? Can we reduce hum ....?
I wish I understand the whole thing. This is hardcore math!
Great video and tutorial - thank you very much for the information. How would you handle a fixed bias push pull circuit such as a Princeton 6g2 layout? Any suggestions regarding the Inversion and injection point into the 2 power tubes?
Thanks for watching. It is a solution for single-ended amps only. Because: Rule 1: PP configurations are hum canceling circuits. Rule 2: The PP tubes have grounded cathodes, which makes the PP configuration absolutely & positively deathly quiet. If not, then 1) one or both of the tubes is/are getting old, 2) the power filter caps on the 5Y3 are suspect or 3) the preamp tubes are the problem: old tubes or the connection to the input jack is creating a hum (ground loop issue).
@@deepblueharp Makes sense - thanks for the response!
It works! Thank you for posting. I have one question though. Could you put a variable 20k resistor in place of the Rhum?
+Christopher Chirico Yes, you can if you have space. Thanks for watching and I am glad it worked for you.
HI, I am going to try the 20k pot today. I just wanted to clear up something first, If you have time. I did not have a center tap on my 6.3 v secondary and used the 2 x100ohm to create one. This center tap lead would then go to the wiper on the pot and the 1 and 3 would go to the respective V1 and V2 cathodes directly on the tube pins. Correct?
Great Video. I've ben using similar cicuits for years. In some amps I can even get a boost on some frequencies... Funny how most well know Amp Mod Guru's don't know anything about Noise Canceling Inverting Loops. These work well and you don't need to add a big cap.
i guess I am pretty randomly asking but do anybody know a good site to watch newly released movies online ?
@Fisher Terrell Flixportal :)
@Eugene Javion Thanks, I went there and it seems to work =) Appreciate it!
@Fisher Terrell Happy to help :D
could it be done in a PI to PP output stage?
I still have hum in my push pull build using this setup, any other tips for dc elevated heaters?
I will share some general information because I don't have a photo of you chassis. If you still have hum, the top issue is generally wiring. The wiring must be absolutely neat. If you look at a Fender Deluxe, you will notice all the wires are no longer than required to connect between 2 points. There must be NO EXCESS wire. Excess wire acts like an antenna to pick up noise from the B+ or Heater wires. All the wiring needs to be laid flat against the metal chassis so the chassis can absorb and ground out any interference that is causing the hum. If a wire needs to cross another wire it must cross at a 90 degree angle. Also, do not run any wire along the side of a component (cap, resistor, etc.) Wire must cross over the component at a right angle or not at all. Wiring at a socket or a pot is a challenge because that last inch at the lugs requires running wires in parallel. (UGH), but just 1/8 inch of separation can make the world of difference. Tube amp wiring is challenging.
Awesome amazing masterful!
Hi, very interesting technique. I wonder why does V2 has two resistors, is to implement correctly? because usually there is only one resistor with a capacitor. Secondly, does it need the filter capacitor on the cathode resistor or it will still work without the capacitor? Thank you
On the cathode: one resistor is 1 ohm to take a direct measurement of the current the other sets the bias. The cathode does not need a bypass capacitor for this to work.
@@deepblueharp thank you!
How would you use this technique on a class AB push pull tube amp where the cathode is grounded on the power tubes ?
I had this question sent to me last week and I have had time to think about it more.
I really wouldn't suggest doing this with power tubes of a AB amplifier. The cathode will need to elevated and the RC filter needs to be rated for 7 watts. However, it can be done. The cathode of the power tube needs to be elevated to 2VDC to 5VDC and a resistor (10W rated) connected from the cathode to the output of the preamp (generally the second stage). It is the preamp that is normally the source of the hum that needs corrected. So...
What would be better is to elevate the ground on the preamp section. Connect the centertap of the 6.3VAC filiment to the RC filter of the preamp second stage (it is normally at 1VDC). Then connect a resistor from there to the cathode of the first stage of the preamp.
@@deepblueharp can you do a schematic for this
hi your video help me a lot, but my circuit only have preamp, can i do it whit only 12ax7? ( sorry for my English I'm peruvian )
+Jonathan Fernandez yes.
Sir, let's say I want to use oscilloscope on my computer (PC software). Can I hook amp an amp (Speaker taps) to a PC? How one can do that?
No, you cannot hook your PC to an amp or any other high voltage device. It will require an interface that will isolate your pc from the devices (like the amp or speaker). The isolation devices will output safe voltage levels for the pc (under 5 volts). I have no recommendations for you. I use an oscilloscope that has outputs to send to a pc to safely acquire data.
Okay, thank you. Any advice about parameters which good oscilloscope should have?
I would suggest looking at the Hantek HT6022BE20MHz 6022be PC based usb digital storage oscilloscope's specifications. Also, it is really inexpensive.