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6l6 in parallel with el84 with non lethal voltage

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  • #16
    Thank you very much for the information

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    • #17
      Originally posted by J M Fahey View Post
      ......Closest he could get to that goal was building a preamp using 12AU7 which are the ones which can work with lowest voltage and drive a chipamp.
      He could do nothing useful with power tubes under those constraints.
      ^^^^^^That. I'm not sure what the goal is here. If it's just experimentation, fine. If the goal is to have an amp that actually sounds like a tube amp, it's not going to happen at low voltages. Best to use a SS amp, IMO.
      "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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      • #18
        OK. I did my math and saw that nothing can be done. So are there any suggestions that will protect me from the electrocution. I have the knowledge to understand that tubes do not work at such low voltages and why. I started this thread because I have 2 major concerns.

        First not to get killed from electrocution. There are no second chances with fatal mistakes.

        Second and most important is to avoid accidents from happening to other people who touch the chassis and not to have any responsibities when fatal accidents happen to other people.

        Thank you

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        • #19
          You protect yourself from electrocution by respecting the electricity. The power in your wall socket can kill you, you can electrocute yourself working on a table lamp. Hobbling the circuit is not the way.

          Don't stick your fingers in it.

          I work on tube circuits with up to 800 volts on them, or for that matter CRT anodes with 30,000 volts on the cup. I feel perfectly safe because I am not going to lay my skin on anything live. I respect the circuit and have knowledge of it. THAT is the key.

          I don't mean this unkindly, but trying to run tubes on 50 volts to prevent electrocution is like driving your car down the interstate at 20 miles an hour to prevent high speed collisions.
          Education is what you're left with after you have forgotten what you have learned.

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          • #20
            I remember first working on amplifiers with live voltages as something that made me very nervous. What made me less nervous is the act of doing it more and more over time. What I recommend before building something is to become comfortable checking voltages and working on amps in general. When I finally built a tube amp that I designed it all fell into place. It is a lot like learning to crawl then you start walking upright and eventually your running. If you bite off more than you can chew... well you know.
            When the going gets weird... The weird turn pro!

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            • #21
              Thank you. All I will have to do is find an expert in my local area to learn how to manipulate high voltage circuits and to a point where I can get a certificate. Because you know when I give my amps to my friends I want to sleep well at night. This is my biggest fear and it is want forced me to buy so many tubes to use them in parallel to maintain the low voltage. I am also considering to increase filament voltage for higher anode current (yes I know That is stupid and can shorten tube life if not destroying it instantly)

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              • #22
                I realize there are two different ”schools” concerning tube audio design. One school basically recognizes something like a triode tube as the most ideal linear amplification device ever. This school praises tube amplification for its high linearity and low distortion. The school treats tube circuitry as means for “transparent” amplification.
                Then there is the other school, which praises tubes for exactly the opposite effect and recognizes them as most ideal distorting devices ever. This school exploits tubes for their non-linearity and uses tube distortion as deliberate effect. The school treats tube circuits as effect processors, which should ideally be everything but transparent and should portray a characteristic known as “tube sound”.

                Yes, I realize there viewpoints are very contradicting but that’s how it goes. I’m also not going to comment if either of those viewpoints is incorrect or correct. For the record, I think most guitarists and amp/effect designers would fall into the second school.

                Given that idea that tubes should be operated at high voltages is based on the principle that tubes generally operate most linearly and have highest headroom at those high voltages (they were designed for) we need to recognize that such idea is largely “school #1’s” idea of how tubes should be employed. For those in “school #2” this may not be the ultimate approach because high linearity and headroom means that the tubes will not necessarily produce praised tube distortion at all, or may do it in magnitudes that have no practical purpose. For them transparent amplification defeats the purpose of acquiring “tube sound”.

                So, if the design goal is to produce distortion with the tube then operating them at decreased supply voltages (i.e. “starved plate”) may not be all that bad idea. The legendary Laney Klipp amps, for example, operated their tube distortion stage at supply voltage of only about 80V and today we have seen a massive increase in all kinds of “power scaling” circuits, which are essentially based on reducing supply voltages to acquire distortion from the tubes at earlier point than usual. Butler’s “Tube Driver” –style effects with low supply voltage also seem to enjoy a lot of success, still. For “effect processing” I wouldn’t regard the idea as overly sacrilegious.

                Yes, wiser people will likely know if power pentodes or beam tetrodes, such as EL84 or 6V6 respectively, can even operate at such low voltages where you can still extract some output signal from "preamp" tubes such as 12AX7 or 12AU7. One thing’s for sure: you will not get much of power amplification out of them at those reduced voltages. Then again, it probably isn’t the point either.
                By the way, there are vacuum tubes that are specifically designed to work at considerably lower supply voltages than those "generic" audio tubes we typically employ. Look for subminiature tube types, VFD's and Nuvistors. The latter were specifically designed to compete with early transistors and associated lower power supply voltages. One could power them, for example, using a 12V car battery.

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                • #23
                  Thank you Teemuk for providing this useful information. I don't like to be an annoying person I just don't want to give up this idea so easily even if at the end I will not succeed. The information is what I'm looking for.
                  So I have a new question to post:
                  If we were to attempt a pentode connection with our operating conditions can we calculate by ourselves what effective load resistance
                  must the pentode drive for maximum power without having to look at the data sheets because they use conventional operating conditions. If you can't post an example I'll be grateful.
                  Also to avoid higher than 100 volts voltages I thought to put 40 volts on the anode and 100 volts at screen and the preamp too. I just don't want the transformer to get the 100 volts. But higher screen voltage than anode doesn't seem right to me even I don't exceed power ratings. Thank you all

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                  • #24
                    You will not make a usable amplifier using +40V on plates,which is below 6L6 saturation voltage.
                    Don't waste your time following that dead end road.
                    OK. I did my math and saw that nothing can be done.
                    I have the knowledge to understand that tubes do not work at such low voltages and why.
                    Cool, then please do not insist on trying to do it anyway over and over.
                    So are there any suggestions that will protect me from the electrocution.
                    Yes,do not stick your fingers inside.
                    I started this thread because I have 2 major concerns.
                    First not to get killed from electrocution. There are no second chances with fatal mistakes.
                    You won´t unless you do it on purpose. Will you?
                    Second and most important is to avoid accidents from happening to other people who touch the chassis and not to have any responsibities when fatal accidents happen to other people.
                    A grounded chassis is SAFE.

                    Given all your constrictions and that you still want to use your tube stash you should have a normal Tube amplifier made by somebody qualified, period.

                    You should buy one of these safety warnings and stick it to your amplifier back panel:



                    They are available at Electrical supply shops or can be ordered online.
                    Last edited by J M Fahey; 05-28-2019, 11:46 AM.
                    Juan Manuel Fahey

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                    • #25
                      Found this in an article on screen grids (posted by soundmasterg here: https://music-electronics-forum.com/...l=1#post330282 )

                      screenvolt.pdf

                      Note how power output drops with decreasing Vp/Vs.
                      Last edited by Helmholtz; 05-28-2019, 01:59 PM.
                      - Own Opinions Only -

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                      • #26
                        Thank you all

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