Then the "old" amp is wrong too. Perhaps you should take the time to understand what you have done.
That also is not "common". There are only two "common" SE topologies - series and parafeed - and your description seems to combine the two. If you take a look at the first two diagrams on this page, you will see the difference.
Thanks tubelab for the diagrams.
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Yes my other amps are parafeed (one primary is to ground is what I meant). Today I've done lot of searching but have not come across a schema that is the way I have it. Now even I think it's strange and again I've just copied it and technician said it was fine. It never crossed my mind to question it till now. As for power, it's got heaps of power compared to other commercially build amps I have. I'm driving big old 70's Advent speakers that aren't particularly efficient, I think around 90db and it's not lacking anything or distort at high levels. So what do I have here than? Maybe someone that has a test amp on the bench can try to swap couple of wires like I have it and see what it does. I agree from looking up other schemas, this shouldn't work as well as it does.
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I just remembered something! The OTs I'm using on the 6V6 are designed for EL84. 6V6 has 80k RA and EL84 has 38K by my tube data. That's 40K difference. Is it possible that this compensates for the resistor from the G2 to Anode on the "conventional" design and the tech knew that and that's why he said it was fine that way? I'm grabbing at straws here.
Either the technician is talking nonsense or you have misunderstood him; technicians talking nonsense are not as rare as you might hope. There is no point in someone else trying your strange wiring; can't you just accept that what you have drawn is wrong? It may or may not be what you have built.
"RA" (actually ra or rp) is irrelevant. That is the anode impedance; nothing to do with the recommended load impedance for a pentode.
"RA" (actually ra or rp) is irrelevant. That is the anode impedance; nothing to do with the recommended load impedance for a pentode.
What I'm going to do is to redo the output to either parafeed or the conventional and see how it goes. I need to get to the bottom of this otherwise it'll never make sense to me.
By this Fender Champ schema http://tknives.com/classact/champ_5e1_schem.gif
the only thing I have wrong is that my B+ is going to Anode instead of G2. So I just need to swap that. No matter how I look at it, I can't see anything else I need to do. Is this it?
the only thing I have wrong is that my B+ is going to Anode instead of G2. So I just need to swap that. No matter how I look at it, I can't see anything else I need to do. Is this it?
I MUST APOLOGIZE to you guys, DF96 you were right in the first place about the error in the schema even tho I checked it several times. I should have counted the pins instead of reading the numbers from the socket. My B+ is indeed on G2 as it should be, I've just opened the amp up to switch the wires and it's actually correct. Anode to OT and B+ to G2. Again, sorry for wasting your time.
An externally hosted image should be here but it was not working when we last tested it.
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It's not a waste when a mystery gets solved. Even though you didn't know your mystery was a mystery, according to your drawing, we pretty much knew you didn't quite have a handle on the situation. Upside-down sockets and pin counting can flip anyone. Now aren't you glad someone didn't rewire their amp to do your experimentation for you?
Well I'm glad I've opened it up a noticed it's right after all. I was working on the amp for about 15 hours straight, than I did the schema and checked several times but I guess was tired not even realizing I did it wrong. Think I'll leave schemas for the next day from now on.
^This.
We learn more from identifying and correcting our own errors than from always getting it right.
Congratulations on two things - identifying the problem, and admitting to it!
Trying to get frequency respose readings
I'm trying to figure out frequency response of my tube amps using software oscilloscope using 20hz-20khz sweep but getting some readings I don't understand. On the tube amps there are some peaks which I'm not sure what they mean (distortion/harmonics?). I've also taken readings from some SS amps I have in workshop to compare. These don't have the peaks apart from the Onkyo.
If I'm reading correctly, the best FR curve is from 6SN7 - 6V6 tube amp (no NFB) but it doesn't sound very powerful and is little flatter. The best sounding is the 12AX7 - 6V6 6wats amp in my ears yet the curve looks weird like the Vector and has spikes. What should I make of these reading?
I'm trying to figure out frequency response of my tube amps using software oscilloscope using 20hz-20khz sweep but getting some readings I don't understand. On the tube amps there are some peaks which I'm not sure what they mean (distortion/harmonics?). I've also taken readings from some SS amps I have in workshop to compare. These don't have the peaks apart from the Onkyo.
If I'm reading correctly, the best FR curve is from 6SN7 - 6V6 tube amp (no NFB) but it doesn't sound very powerful and is little flatter. The best sounding is the 12AX7 - 6V6 6wats amp in my ears yet the curve looks weird like the Vector and has spikes. What should I make of these reading?
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
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Nothing there makes sense...
Applying a frequency sweep (it needs to be slow) is one thing. You could then visually observe the amplitude across the load and note the -1 or -3db points visually. No amplifier should have in band peaks and dips.
I'm sure there will be software to plot a response graph but you can't do that on a 'normal' oscilloscope very easily.
Applying a frequency sweep (it needs to be slow) is one thing. You could then visually observe the amplitude across the load and note the -1 or -3db points visually. No amplifier should have in band peaks and dips.
I'm sure there will be software to plot a response graph but you can't do that on a 'normal' oscilloscope very easily.
Hi,
I'm not a specialist, but here's how I do it:
- Inject noise using noise generator instead of a frequency sweep (there is lots of free software for noise generation)
- Use fourrier transform analysis software set in "averaging" mode for 10 seconds. That should show the frequency dependent power envelope and hence you will quickly be able to tell the relative difference in gains at different frequencies. (I use JAAA on Linux to do this).
Hope this helps.
Regards
I'm not a specialist, but here's how I do it:
- Inject noise using noise generator instead of a frequency sweep (there is lots of free software for noise generation)
- Use fourrier transform analysis software set in "averaging" mode for 10 seconds. That should show the frequency dependent power envelope and hence you will quickly be able to tell the relative difference in gains at different frequencies. (I use JAAA on Linux to do this).
Hope this helps.
Regards
Ok, I'll try that even if I have to install Linux. I want to find out why some amps I build sound better than the others. I hope that will help me to tweak the design and even select output trafos for the sound I like since I think I could test them in circuit and see the frequency. The way I do it now is mostly by listening and that can be very unreliable from day to day so it takes days of listening to be sure.
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I think you will find that subjective differences come down to much more than frequency response.
If you have a frequency sweep generator then initially look at the output of just that on the scope as a way to confirm that the amplitude is constant over the sweep. If you set the scope to a low timebase sweep setting you will be able to see the amplitude of the 'envelope' rise and fall at the extremes of the frequency band. 20 to 20kHz isn't really wide enough to show where things start to roll off for most (certainly solid state) amps. 2Hz to perhaps 100kHz would be more realistic.
If you have a frequency sweep generator then initially look at the output of just that on the scope as a way to confirm that the amplitude is constant over the sweep. If you set the scope to a low timebase sweep setting you will be able to see the amplitude of the 'envelope' rise and fall at the extremes of the frequency band. 20 to 20kHz isn't really wide enough to show where things start to roll off for most (certainly solid state) amps. 2Hz to perhaps 100kHz would be more realistic.
In order to explain strange plots we need to know exactly what you have done. You have told us almost nothing.
As a wild guess I would say that you are sweeping the frequency far too fast, and possibly overloading the amplifier with too big a signal, and possible have some instability due to poor equipment setup or misbehaving circuits.
As a wild guess I would say that you are sweeping the frequency far too fast, and possibly overloading the amplifier with too big a signal, and possible have some instability due to poor equipment setup or misbehaving circuits.
There may also be issues with sound settings on the computer (e.g., effects not turned off). The periodicity of the peaks and valleys possibly suggest a time delayed signal being mixed with the desired signal.
First thing before injecting any signal is doing a zero measurement to verify that test equipment does not contribute significant noise.
Second
I would not go for jaaa or japa, these programs are not versatile compared to ARTA. I know what I am talking about, because I used them all on my linux machine. ARTA works flawless under wine, meanwhile a bought a licence just to honour the author for this great piece of software.
Second
I would not go for jaaa or japa, these programs are not versatile compared to ARTA. I know what I am talking about, because I used them all on my linux machine. ARTA works flawless under wine, meanwhile a bought a licence just to honour the author for this great piece of software.
On slow sweep the output seems to be reasonably constant, I won't even go in to numbers because I have no idea how accurate the PC is, there is a lot of background noise in there, the 20Hz peak is just one of those with nothing connected. But I had to give it a shoot. I will try the Linux tho. I don't need much, just something to confirm that what I'm hearing is roughly correct.
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