Hi everyone,
i finished my first tube amp yesterday and went to turn it on today but it does stuff it's not supposed to.
The Amp uses 6n1p's driving EL34's connected in Triode mode, i got the schematic from a friend who has experience with tubes and built multiple amplifiers already so i trusted him on that..:
The speaker connected to the left channel emits a continuous popping sound and when applying an input signal it comes out as extremely distorted.
The right channel has another issue, it's quiet at first but then starts emitting a distorted sounding hum that gets louder as the tubes warm up to the point where i have to turn the amp off to not damage my speakers.
I swapped out the tubes but the issues persist so i don't think they're faulty.
I also double checked every connection and wire and could not find any issue.
Here's an image of the guts, i know it's far from perfect:
So yea, if anyone has an idea about what could be wrong please tell. Maybe it's even the schematic itself that can't work that way? He told me he based it on an existing design and modified it..
Thanks in advance!
i finished my first tube amp yesterday and went to turn it on today but it does stuff it's not supposed to.
The Amp uses 6n1p's driving EL34's connected in Triode mode, i got the schematic from a friend who has experience with tubes and built multiple amplifiers already so i trusted him on that..:
The speaker connected to the left channel emits a continuous popping sound and when applying an input signal it comes out as extremely distorted.
The right channel has another issue, it's quiet at first but then starts emitting a distorted sounding hum that gets louder as the tubes warm up to the point where i have to turn the amp off to not damage my speakers.
I swapped out the tubes but the issues persist so i don't think they're faulty.
I also double checked every connection and wire and could not find any issue.
Here's an image of the guts, i know it's far from perfect:
So yea, if anyone has an idea about what could be wrong please tell. Maybe it's even the schematic itself that can't work that way? He told me he based it on an existing design and modified it..
Thanks in advance!
Alright, just connected pin 1 to 8 on both tubes and the hum issue still persists. Disco, you're completely right, gonna order new ones immediatly.
Two gain stages to drive a single EL34, without NFB?
That's way too much gain.
And I'd use a much higher value resistor to decouple/filter the HT for the gain stages. 220R is too low.
That's way too much gain.
And I'd use a much higher value resistor to decouple/filter the HT for the gain stages. 220R is too low.
The popping could be 'motorboating' and possibly related to how you have the grounds connected together.
Motorboating (electronics) - Wikipedia
As to the other channel. well it might be worth you removing the E34 on the popping left channel and doing a quick check on the DC conditions of the right EL34, in particular checking that the cathode volts doesn't rise beyond where it should be. If you are running at around 60 milliamps (I think that would be in the right ballpark) then that means around 30 to 35 volts across the 560 ohm. Much more and you will be pulling the rail down.
If that is OK then is that channel now quiet?
If not then isolate the 0.22uF coupling cap and retest. It should be quiet as you only have the EL34 stage connected and the DC conditions should be stable.
Assuming it is quiet then you have to look at the front end to see why it is generating unwanted hum and again, the wiring layout and where grounds are returned often comes into things.
Motorboating (electronics) - Wikipedia
As to the other channel. well it might be worth you removing the E34 on the popping left channel and doing a quick check on the DC conditions of the right EL34, in particular checking that the cathode volts doesn't rise beyond where it should be. If you are running at around 60 milliamps (I think that would be in the right ballpark) then that means around 30 to 35 volts across the 560 ohm. Much more and you will be pulling the rail down.
If that is OK then is that channel now quiet?
If not then isolate the 0.22uF coupling cap and retest. It should be quiet as you only have the EL34 stage connected and the DC conditions should be stable.
Assuming it is quiet then you have to look at the front end to see why it is generating unwanted hum and again, the wiring layout and where grounds are returned often comes into things.
Put some feed through rubbers on those holes, it won't fix the problems you experience but it will make your amp a little bit safer.
Hm yes, would you recommend just using one triode of each 6n1p? Which resistor would you suggest? 10K?
Will measure voltages in a bit, i already removed the tubes one by one to try and isolate the issue and have the hum isolated to the gain stage of the right channel. I basically have one ground rail per channel and both of those are connected to the power supply ground, could it have something to do with the signal ground coming from the pot only being connected to the ground rail of the right channel?
Good point, will be adding this.
If you want to drop the gain remove either or both the 100uF/16v on the cathodes to ground. There's not much decoupling for the power supply on the first stage 220R is very low maybe 4k7 or 10k so the hum/instability will get in there. The high gain in combination with poor power supply decoupling may well cause popping. The anode resistor for the first stage is quite low. Maybe you should try the first stages on ltspice there are valve models on diy audio.
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Coming from B+, the combination of a 220 ohm series resistor and 10uF parallel capacitor will provide very little power supply ripple filtering. It's not just that the resistor is too low in value; the capacitor is too low in value as well.
The first thing I would do is make the resistor 2.2k ohms and the capacitor 47uF.
47uF 500V electrolytics are easy enough to find.
The formula for in-the-ballpark-adequate filtering is for fc to be equal to or less than about 2Hz (fc = 2Hz)
fc = 1/2piRC (C in Farads)
1/6.283*2200*47uF = 1.54 Hz
A shortcut is to make R (in ohms) * C (in microfards) = 100,000 to 200,000.
2200 ohms * 47uF = 103,400
The fc for your combination of 220 ohms and 10uF is
fc = 1/6.283*220*10uF = 72.35 Hz [!!!]
Using the shortcut, 220 * 10 = 2200 (far short of the 100,000 target)
That won't filter any 60Hz hum at all, and won't suppress 120Hz ripple much either.
If you really want to use that 10uF cap then the series R should be 10k ohms, and that might drop more volts than you want. But it might be okay.
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Check for cold solder joints. Popping noises can be caused by those.
It's not likely, but the hum building to the point that you have to turn off the amp sounds like a leaky coupling capacitor (letting DC through to the output tube grid). Check DC voltages at each tube's grid. It should be 0VDC at all of them.
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I would also add another RC decoupling between the two 6N1P stages.
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The first thing I would do is make the resistor 2.2k ohms and the capacitor 47uF.
47uF 500V electrolytics are easy enough to find.
The formula for in-the-ballpark-adequate filtering is for fc to be equal to or less than about 2Hz (fc = 2Hz)
fc = 1/2piRC (C in Farads)
1/6.283*2200*47uF = 1.54 Hz
A shortcut is to make R (in ohms) * C (in microfards) = 100,000 to 200,000.
2200 ohms * 47uF = 103,400
The fc for your combination of 220 ohms and 10uF is
fc = 1/6.283*220*10uF = 72.35 Hz [!!!]
Using the shortcut, 220 * 10 = 2200 (far short of the 100,000 target)
That won't filter any 60Hz hum at all, and won't suppress 120Hz ripple much either.
If you really want to use that 10uF cap then the series R should be 10k ohms, and that might drop more volts than you want. But it might be okay.
--
Check for cold solder joints. Popping noises can be caused by those.
It's not likely, but the hum building to the point that you have to turn off the amp sounds like a leaky coupling capacitor (letting DC through to the output tube grid). Check DC voltages at each tube's grid. It should be 0VDC at all of them.
--
I would also add another RC decoupling between the two 6N1P stages.
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It is quite possible yes, and it all depends on what feeds into and out of those grounds. A few cm of wire is more than enough to develop a significant volt drop across, voltage that is of course related to the current flow in that wire.
All the signal grounds should go to a clean point of your choosing that you then call signal ground.
As an example lets take your circuit as drawn, and lets suppose the 10uF cap ground links to the ground symbol at the 1k cathode resistor of your first stage. Now look where your return back to the power supply is (as you've built it, we can't tell from the diagram). Any ripple component passed though that cap is developing a small ripple voltage along all the wiring back to the power supply.
Suppose that PSU return is taken from the earthy end of the 560 ohm as drawn.
You now have a nice ripple voltage applied between the two 1k's and the 470k grid resistor which is seen by the stages as a valid signal and so gets amplifier.
Two years later.. sorry for not replying anymore, life got in the way. I have since found the issue, it was a bad signal ground connection on the pot. Fixing that made the amp work however there were some hum issues, i have since re-done the wiring completely and added another choke to the power supply, it's now 10µ-10H-100µ-1.5H-100µ and it's dead quiet even on my efficient (~95db) speakers.
I recently got into LTSpice and designing my own tube amps, this amplifier has since been re-designed a few times. right now it uses E83F's driving the EL34's with decent results.
Thanks everyone for helping, better late than never 🙂
I recently got into LTSpice and designing my own tube amps, this amplifier has since been re-designed a few times. right now it uses E83F's driving the EL34's with decent results.
Thanks everyone for helping, better late than never 🙂
Hello disso, in another previous thread I posted a simililar project now at beginning plannd with 6p3s then changed to EL34 (and now running like this) as yours.
Apart your troubles discussed here with the possible solutions, could you tell me where did you find the schematic? It seems a project similiar to the one of an italian electronics magazine, with the drivers running as compound amplifier (they was ECC82).
PS: as minor priority about things-to-do to the amp, I'd suggest to create a virtual ground for the heaters (in particular of the driver tube). As for me, I've always been happy like that.
Thanks
Back then i didn't know a whole lot about tube amps/electronics in general so i asked a friend of mine who was into audio and had already built some tube amps himself for some advice. Originally i wanted to build Mikael Abdellah's
EL34 amplifier from diyaudioprojects.com but my friend told me the voltage is too high for a beginner project and gave me the schematic i posted here. He's an old fashioned guy and doesn't really use the internet, especially not for his electronics projects, he mostly gets schematics and information from magazines and books. That schematic indeed originates from the "nuova elettronica" magazine from italy and as far as i remember it does use an ecc82. He then combined that with the tubes i already had (6N1P). Now i know that that schematic isn't really optimal and one half of a 6N1P is enough to drive an EL34.
I did virtually ground my heaters with 2x100R 🙂
Yes, I meant exactly from the magazine you mentioned. Apart the non-ideal circuit in the case the other issue from that project, as far as I've know, was the lacking quality of the OT's. In fact dimensionally those were tiny ones, more suitable with EL84 maybe, but I don't remember if they were 5k.
Now you say you turned to a pentode as driver tube, just for sake of information is there any particolar reason to the E83F? I know few other projects running with the EF86, but it differs from yours that seems to be a variable mu tube
Now you say you turned to a pentode as driver tube, just for sake of information is there any particolar reason to the E83F? I know few other projects running with the EF86, but it differs from yours that seems to be a variable mu tube
I don't remember the OTs, i just know that you could only order them from the magazine and since that's from the 1990s nothing's available anymore.
I'm using E83F because i had some and wanted to try something different, they are running in triode mode and are LED biased. Output power isn't too great, should be 2-3W. I might try pentode in the future, this is the first circuit i designed completely from scratch using LTSpice.
I think if you read Rongons' note the first stage B+ 220R and 10uF will be letting the hum in. A simple change to a cheap 47uF electrolytic and 4k7 would have saved you the trouble of having to have two chokes in the power supply. In LTspice if you add some 100Hz on top of your B+ supply you can see how good the B+ rejection is.
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Yea i'm sure that was one of the issues, another one being the wiring and not having a star ground. I now have that and i also have 100R-47µ for the first stage.
super, yep take the rectifier return current to the ground of the first cap - star grounding is a simple way of enforcing this rule stopping this current entering the signal wiring. Maybe have a go at building something a little bigger. Your circuit has two first stage amplification - so quite a lot of gain, one stage may have done.
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