help understanding amplifier schematic

[audioguru]

how do i know if the tubes are ok or not?

You turn back your clock to about 1951 and test the tubes at your local convenience store. They sold cigarettes and vacuum tubes.

 

[whiz115]

If you're using the original circuit you posted, then (like we told you) it's rubbish.

Add the decoupling components as shown in the two diagrams I posted, R5, R6, C1A and C1B in the second of the diagrams - without them you're just feeding hum from the PSU directly to the grids of the valves.

i wouldn't say it's rubbish... it's just a basic amplifier circuit...
what i need is to get rid the noise and i'm happy with it.

can you tell me how i'm going to implement your above advice? because the only thing i managed to do is to ground my signal.

 

[audioguru]

Make a very good-sounding solid state amplifier with a tube glowing on top.

 

[flat5]

Do you have a light dimmer in use? Your audio file sounds like a buzz to me. Not 50 or 100 hertz...unless severe clipping is causing me to hear only harmonics.

Pull the first tube out of the circuit and see if all the noise goes away, please.

 

[Bob Scott]

Is the metal chassis connected to power supply minus (like it should be)?

 

[Nigel Goodwin]

i wouldn't say it's rubbish... it's just a basic amplifier circuit...

No, it's rubbish

It has no feedback, so it's even higher distortion and poorer frequency response than other valve amps, but required parts are left out so it feeds hum to the grids.

what i need is to get rid the noise and i'm happy with it.

can you tell me how i'm going to implement your above advice? because the only thing i managed to do is to ground my signal.

Look at the circuits I posted earlier, and the decoupling components between the HT rail and the triode anodes - these are absolutely essential.

 

[whiz115]

Is the metal chassis connected to power supply minus (like it should be)?

yes... ofc without it i'm getting some extra noises..

Do you have a light dimmer in use? Your audio file sounds like a buzz to me. Not 50 or 100 hertz...unless severe clipping is causing me to hear only harmonics.



Pull the first tube out of the circuit and see if all the noise goes away, please.

Where are you flat5? give us a hand here!

no i'm not using any dimmers...
well...the quality of the audio file is not so good because it's from my mobile phone but i guess that the guys are right because i measured it and it is 50Hz and 100Hz

ok i removed the ECC83 and the noise still exists so are we close to something or not?

Look at the circuits I posted earlier, and the decoupling components between the HT rail and the triode anodes - these are absolutely essential.

nigel i did that and i only manage to ground my input signal....
i did it as is in the circuit... 10K resistors in series with 22uF/400V decoupling capacitors and then the resistors of my circuit.

probably i did wrong with the values of the first resistors?!



btw Nigel.... this guy sells some pretty good amp kits like the discontinued from national LM3875 etc... and he has also made an tube amp like mine but he doesn't makes any complaints about noises...
Mikkel Corydon Simonsens hjemmeside

as i said i only want to get rid of the noises...and i'm satisfied with the amp...i knew from the start that it has lower output power (though it's NOT so low as you might think!)

the only thing i didn't knew is the very high distortion from the middle of the volume control and after....but it's OK for what i'm going to use it with.

thanx.

 

[Nigel Goodwin]

Like I keep saying, you're feeding the PSU hum directly into the grids, if you remove the triode (which is always a good thing to do in valve circuits) the hum is still feeding directly through the anode load of the triode in to the grid of the EL84.

nigel i did that and i only manage to ground my input signal....

I don't know what you mean?, try posting the circuit as you modified it.

i did it as is in the circuit... 10K resistors in series with 22uF/400V decoupling capacitors and then the resistors of my circuit.

probably i did wrong with the values of the first resistors?!

Resistor values make VERY little difference.

btw Nigel.... this guy sells some pretty good amp kits like the discontinued from national LM3875 etc... and he has also made an tube amp like mine but he doesn't makes any complaints about noises...
Mikkel Corydon Simonsens hjemmeside

He won't get the problem you have, he has the required components - see the 2K and 50uF to the 2nd triode, and 16K and 16uF to the 1st triode.

as i said i only want to get rid of the noises...and i'm satisfied with the amp...i knew from the start that it has lower output power (though it's NOT so low as you might think!)

Distortion sounds a LOT louder than clean sound, which is why many guitarists love valve amps

the only thing i didn't knew is the very high distortion from the middle of the volume control and after....but it's OK for what i'm going to use it with.

If it's very high distortion, it's probably becuase you're over driving it - bear in mind it's a guitar amp, you could leave off the first stage to just feed an MP3 player to it.

 

[whiz115]

I don't know what you mean?, try posting the circuit as you modified it.

first time i only connected the 22uF/400V decoupling capacitors without the 10K resistors and although the noise dissapeared.. i also lost the input signal and i understood that i was filtering the amplified output signal from the tube, second time i also used th 10K resistors but it was the same result as above.

so probably it didn't worked or maybe i did something wrong (?)

He won't get the problem you have, he has the required components - see the 2K and 50uF to the 2nd triode, and 16K and 16uF to the 1st triode.

i wasn't talkin for the amp with the 6SN7 triodes i was talking about the other with the ECC82 and the EL84 but both are similar with mine.

btw mikkel says these words to his site about his simple design with the 6SN7 which is so similar with mine:

"The amp actually sounds fine without feedback, but the bass is a bit "boomy".

although i don't know in which way he is using his amp... to listen music? to play the guitar?!
i just did a small notice of what Mikel Simonsen says and i don't mean that these amps are Hi-Fi.

If it's very high distortion, it's probably becuase you're over driving it - bear in mind it's a guitar amp, you could leave off the first stage to just feed an MP3 player to it.

explain this to me... in case i want to connect an mp3 player i should leave the first triode outside and feed the mp3 directly to the control grid of the second triode? (ofc i'm going to use a resistor in parallel in the input)

is that right?


P.S.

here's the pcb and the component side.... perhaps there's also an error somewhere there and i couldn't see it?

 

[Nigel Goodwin]

first time i only connected the 22uF/400V decoupling capacitors without the 10K resistors and although the noise dissapeared.. i also lost the input signal and i understood that i was filtering the amplified output signal from the tube, second time i also used th 10K resistors but it was the same result as above.

so probably it didn't worked or maybe i did something wrong (?)

You did something wrong - you need a resistor and capacitor to decouple the power to the triode preamps - as shown in both the diagrams I posted, and in the 6SN7 one. Without it you're going to get massive hum.

i wasn't talkin for the amp with the 6SN7 triodes i was talking about the other with the ECC82 and the EL84 but both are similar with mine.

btw mikkel says these words to his site about his simple design with the 6SN7 which is so similar with mine:

Again, it has decoupling - so it works - your's doesn't so it will buzz all the time.

"The amp actually sounds fine without feedback, but the bass is a bit "boomy".

Depends what you mean by 'fine'

It's low quality, but that may be fine for what you want - particularly for guitar use.

explain this to me... in case i want to connect an mp3 player i should leave the first triode outside and feed the mp3 directly to the control grid of the second triode? (ofc i'm going to use a resistor in parallel in the input)

is that right?

You feed it through a capacitor to the grid - or, as it's working, just don't turn it up so far.

here's the pcb and the component side.... perhaps there's also an error somewhere there and i couldn't see it?

Just as a matter of interest, why did you make a PCB for it? - it's not a particularly useful method for a valve amp, especially a home made one.

Here's the layout details for the second circuit I posted, that used a double triode

 

[whiz115]

Just as a matter of interest, why did you make a PCB for it? - it's not a particularly useful method for a valve amp, especially a home made one.

Here's the layout details for the second circuit I posted, that used a double triode

i didn't wanted any pcbs i wanted it to be with the old fashioned way... but the problem with the hum made me to use a pcb.

so... i'm going to try again the capacitors to the anodes... and i'm also going to order a 5H/500mA power choke from the shop that did my transformers

i don't know if you agree with the last one.

also could you please help me with the values of the resistors for the anodes-cathodes? i want the tubes to work on normal voltages... and i can't because the schematic is calculated for 250VDC and PSU gives 310VDC.
right now for the triodes i'm using 100K for the anode and 1K for the cathode on both of them...which is not right because i lost the ratio of the original schematic and the EL84 has two 87ohm/2W resistors with a 22uF capacitor in parallel...

right now the el84 has anode 245V and it's still very high


P.S the schematic especially the layout you posted are very useful to me
because i can take ideas for the orientation of the components without using a pcb and in case one day i want to move on to a different design...but still you haven't told me if i can easily substitute the tubes of your designs with the tubes i already have or if it needs many modifications.

 

[Nigel Goodwin]

i didn't wanted any pcbs i wanted it to be with the old fashioned way... but the problem with the hum made me to use a pcb.

I fail to see any connection between lowering hum and making a PCB? - in fact the total opposite is more likely, you're increasing the length of leads in the chassis, and making it more likely to suffer from hum pickup.

The slassic way of making avalve amp was basically wiring components directly from the valve bases to each other, using small tag strips for any connections not on a valve. Later commercial designs often used tag boards, which (like a PCB) allow the board to be assembled on the production line, then fitted in the chassis later.

The old TV manufacturer KB actually made hand wired colour TV sets, no PCB's in them at all.

so... i'm going to try again the capacitors to the anodes... and i'm also going to order a 5H/500mA power choke from the shop that did my transformers

i don't know if you agree with the last one.

It's always a good idea - but bear in mind it was done back when electrolytics were only 8uF or so, modern high value electrolytics make it of much less value.

also could you please help me with the values of the resistors for the anodes-cathodes? i want the tubes to work on normal voltages... and i can't because the schematic is calculated for 250VDC and PSU gives 310VDC.

Adding the extra resistors feeding the anodes, with capacitors to chassis, will drop the voltage - this won't affect the gain of the stages, which increasing the anode loads will.

right now for the triodes i'm using 100K for the anode and 1K for the cathode on both of them...which is not right because i lost the ratio of the original schematic and the EL84 has two 87ohm/2W resistors with a 22uF capacitor in parallel...

right now the el84 has anode 245V and it's still very high

I wouldn't worry about it, that sounds fine for the output valve.

P.S the schematic especially the layout you posted are very useful to me
because i can take ideas for the orientation of the components without using a pcb and in case one day i want to move on to a different design...but still you haven't told me if i can easily substitute the tubes of your designs with the tubes i already have or if it needs many modifications.

Valves are really simple and crude devices, you can pretty well switch and change as much as you like - a simple amplifier like this could be thrown together in a couple of hours, if you had the valves and the transformers. You could tweak the values afterwards if required.

The diagrams are taken from a book I bought years ago at a second hand bookshop, it originally cost four shillings and sixpence (now that will confuse many readers! - not Eric though ).

 

[whiz115]

ok! so heres what...
my first tube amplifier is almost ready!!

I managed to suppress the noise a bit and now it works better than ever!
but i still have 1-2 things that i want to talk about and find a solution
but these later because now i have something to show you all!

it might be pointless but out of curiocity i got this amp analysed! here's the results and also some photos.

Noise level dBA: -75.9
Dynamic Range dBA: 59.5
Total Harmonic Distortion THD: 59.912%


i think the numbers don't go so well, but to the ear is kinda different...
any comments?

 

[audioguru]

The frequency response and distortion are horrible. Like the sound of a TV about 53 years ago. Some people like that lack of performance.

 

[Nigel Goodwin]

ok! so heres what...
my first tube amplifier is almost ready!!

I managed to suppress the noise a bit and now it works better than ever!
but i still have 1-2 things that i want to talk about and find a solution
but these later because now i have something to show you all!

it might be pointless but out of curiocity i got this amp analysed! here's the results and also some photos.

Noise level dBA: -75.9
Dynamic Range dBA: 59.5
Total Harmonic Distortion THD: 59.912%


i think the numbers don't go so well, but to the ear is kinda different...
any comments?

The distortion figure will include the hum as well, did you fit the decoupling components as suggested? - they should pretty well get rid of it all, not just partially.

However, distortion figures for a non-feedback valve amp are going to be very high anyway.

 

[whiz115]

The distortion figure will include the hum as well, did you fit the decoupling components as suggested? - they should pretty well get rid of it all, not just partially.

well no.. i did some other things first... but i'm about to do it.

as i said before i got 1-2 things to ask, first the plate of the EL84 turns a bit
red!!! (screen voltage is at 220V and anode at 245V and i don't know what causes it.)

Then the input... if i let it floating the amp get's noisy!!! (the input resistor is 1M).

as far as i know the first is because of overvoltage either to the screen or to the anode... but as far as i can tell my voltages are normal!!! if you imagine that some guys work these tubes single ended at 370V and 17W output.
and with very small screen resistors!

 

[Nigel Goodwin]

well no.. i did some other things first... but i'm about to do it.

So you still have masses of hum, this will be added to the distortion reading (because it's distortion AND noise).

as i said before i got 1-2 things to ask, first the plate of the EL84 turns a bit
red!!! (screen voltage is at 220V and anode at 245V and i don't know what causes it.)

Probably too much current, increase the value of the cathode resistor to increase the grid bias on it.

Then the input... if i let it floating the amp get's noisy!!! (the input resistor is 1M).

It probably will, but can be minimised by careful layout and screened cable (connected properly).

as far as i know the first is because of overvoltage either to the screen or to the anode... but as far as i can tell my voltages are normal!!! if you imagine that some guys work these tubes single ended at 370V and 17W output.
and with very small screen resistors!

Like I said, bigger cathode resistor (I'm presuming you've got no positive voltage on the grid?).

 

[whiz115]

So you still have masses of hum, this will be added to the distortion reading (because it's distortion AND noise)

i'll fix it as soon as i correct the new problem.

Probably too much current, increase the value of the cathode resistor to increase the grid bias on it.?).

increasing the cathode resistor i'm also increasing anode voltage...

I'm presuming you've got no positive voltage on the grid?

what do you mean with that?


When all the problems finaly get solved i'm thinking to make my amp work with High input and with low input so i can use it depending what i want to connect.

here's an updated schematic which i'm currently using and works only with the 1/2 of the ECC83


Nigel thanx for all of your help.

 

[Nigel Goodwin]

increasing the cathode resistor i'm also increasing anode voltage...

what do you mean with that?

Why are you obsessed with anode voltage?, it's getting hot because it's dissipating too much power - to reduce this increase the grid bias to reduce the current (this is done by increasing the cathode resistor).

When all the problems finaly get solved i'm thinking to make my amp work with High input and with low input so i can use it depending what i want to connect.

Easy to select either one or two triode stages.

here's an updated schematic which i'm currently using and works only with the 1/2 of the ECC83

That's still feeding PSU hum directly to the grid of the pentode, we've told you repeatedly - ADD DECOUPLING TO THE TRIODE SUPPLY - like all the designs in the world, apart from the totally useless one you're copying

 

[whiz115]

so the changes will be...

for the ECC83 one more resistor 47K before the 100K and between them a 22uF/400V decoupling capacitor.

for the EL84 a 2k2 resistor for the screen which i think it's the recomended value for the EL84... and a bigger value for the cathode probably 150ohm/4W

if i'm not wrong... EL84 must decipate 12W so i'm going to measure the voltage between anode-cathode and the current the tube draws so i can regulate it... is that ok or i'm still obsessed?
i just don't want to destroy something which it isn't as cheap and also it's not so easy to find as a simple transistor


btw my output tube has also a blue glow... and it's very nice! and as far
as i know that can happen with high rush of electrons hitting things inside the tube and releasing photons.