Mark wrote: ↑Wed Sep 07, 2022 11:11 am
I had better things to do than chasing down circuits and building prototypes when the forum was still a Yahoo site, but I did it for the greater good. The forum you see here today is a result of people giving. Perhaps this is your chance to give to the forum.
ok respect.. the young generation all want today something without any effort , so my comment was cumulative for all what i'm seeing last 5-10 years everywhere..open youtube and thats it..all is there. practice is all what is count, here and in other hobbies/works,at least from my point of view and i'm seeing often philosophers.....
I personally tire of hearing this refrain. I'll show you a quote that shows you the timeliness of the 'youth of today' complaint:
“The children now love luxury; they have bad manners, contempt for authority; they show disrespect for elders and love chatter in place of exercise. Children are now tyrants, not the servants of their households. They no longer rise when elders enter the room. They contradict their parents, chatter before company, gobble up dainties at the table, cross their legs, and tyrannize their teachers.”
Guess who said this?
Socrates.
He was born 470 BC.
So 'the young generation' has been a constant failure for almost 2500 years at a minimum, except they haven't.
They're just being young people full of dreams and ideals and they want things just like you did when you were young.
Just because the internet has made information more digestible, easier to learn etc, doesn't mean they don't work, try, and somehow deserve the knowledge less than anyone else.
ok end rant.
~Phil
I don’t have any builds where I can put carbon film resistors into it and then replace them with carbon comp resistors. I suppose the next question is how the results were recorded. What speakers and what mics are used. I don’t have anything to do a decent recording.
I remember hearing a difference in valve rectifiers with my Trainwreck Rocket clone. I would swear black and blue it was different, but the mic in my camcorder captured no difference.
I should point out prior to this I thought the idea of a rectifier affecting the timbre of an amp was rubbish. I thought more compression for sure, but that’s it. Mind you, I still have doubts about what I heard some years ago.
Tony (Dorrisant) sent me some NOS CC resistors to test.
The result of tracing two samples using my uTracer 3+ is shown below. Current vs. voltage appears to be quite linear. Next, the data was dumped into Excel to calculate and plot resistance (V/I) vs. applied voltage for each data point. The uTracer is not particularly good when operating at low voltages, and mine is currently configured for 600 mA capability, so its resolution when measuring one or two mA is a bit compromised. That said, after it is up over 100V, it seems to be getting current values consistent with the resistance as measured with an LCR meter.
Is there some change in the calculated resistance as the voltage increases? Yes, it appears there is, but it is very small with respect to the nominal value measured at low voltage, even when the measurement pulse is 350V. CC resistors are noisy, drift up in value over time, and it doesn't look like there is any significant voltage coefficient effect happening here.
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So basically nothing interesting to see here... as in, no real deviation to call it "mojo" from those plots. I know that there may be a discernible difference with bat or dog ears, but nothing odd about performance. It would be interesting to see a chart on differences over time. In labs, this is usually done by heating them and plotting repeated measurements over a short interval (48hrs) to simulate years of use.
Maybe then it could be compared to CF or MF.
Thanks for doing that test!
"Education is what you're left with after you have forgotten what you have learned" - Enzo
several following tube stages should be built or use some tube amp, and in all anodes carbon comps. in last anode to put serial combo of 10k metal film + 100K carbon comp.
sine wave on the input grid first tube, slowly increasing, 50mV-100mV etc.. up to the some big output on last anode, per example 200Vpp.
measuring with scope or so , all the time on the 10 metal film kohms resistor , expected voltage can be different with the increasing the signal.
also the same setting and test but with all 100k in anodes replaced from carbon comps to metal film/oxide. comparation of measurements.
easier with spectrum analyser, but maybe also REW software with distortion measurements can be used for this, just to take signal from 10k+100k divider over coupling capacitor, and respect to max voltage available to avoid to burn the card.
Last edited by bepone on Sat Sep 10, 2022 11:19 pm, edited 1 time in total.
Thank you Martin and Tony! This looks pretty conclusive. At least it does for the DC case.
I suppose an argument could be made (and to be clear I'm not making one) that there could somehow be some sort of inductance or capacitance associated with certain resistor types that don't show up in a test like this. But for the kinds of frequencies found in guitar amps, I very much doubt this would be significant. If it were you would just say "this resistor is broken!" .
Here is one more resistor trace, this time comparing the same 100K CC from above and a new Vishay-Dale MF. This time I have let the tracer select gain and averaging by setting those parameters to "auto," which seems to produce a smoother trace. The resistors are traced simultaneously, with one on the anode channel and the other on the screen channel as before. Other than the CC resistor being high in value, the characteristics are very similar. Both show a slight upward trend in resistance with voltage, indicating there is no difference between the CC and a MF in that regard, and that it is most likely an artifact of the tracer.
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from this graph above we see nothing , and only can conclude only that utracer cannot test properly the resistance.
so to cut this (wrong) approach, we can use spectrum analyser maybe we can have some real results.
or test them in circuit it is even faster.
put in anode of the first stage carbon comp resistor play the guitar. put metal film the same value on the same place in anode, play the guitar. difference felt? yes=? no? someone tried? all the answers are correct. if yes you are happy, if no you're happy again, and you dont need to discuss about resistors ever again
Is it possible at certain voltages their is a impedance that changes, affecting the signal slightly. Is there a slight capacitance in addition to the resistance? I mean there's no perfect component right?
Tube junkie that aspires to become a tri-state bidirectional buss driver.
How long does it take for the uTracer to create a curve? If it is very fast (like around 1ms or so for 1/4 wavelength of a 4k signal) then any theoretical impedance component a resistor may have would show up in the curve (I think). This would nicely kill two birds with one stone (if the curve stays linear). But my guess is that it may not capture a curve quite that quickly.
The tracer uses a 1 mS pulse, taking multiple readings and averaging them for each data point. The applied voltage goes to zero between each pulse. It takes about one second to acquire each of the 20 data points in the curve.
the young generation all want today something without any effort , so my comment was cumulative for all what i'm seeing last 5-10 years everywhere..open youtube and thats it..all is there.
practice is all what is count, here and in other hobbies/works,at least from my point of view and i'm seeing often philosophers.....
.
