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  1. RogerMod

    Good tube literature

    Who is Jay?
  2. RogerMod

    Power supply for two Mullard 5-10 amps

    The lamp limiter in the mains may exacerbate the problem. Motorboating comes from loosness in a supply and the lamp increases the loosness. Motorboating happens when the output stage is able to drop the B+ enough to have that drop proceed though the power supply to the earlier stages. Tube...
  3. RogerMod

    When we bias a tube amp what are we measuring?

    Yes Ive seen that warning. Depends on your meter doesnt it? On the Simpsons with 5000 volt scales no problem, but then one might turn it to 500 volts to get the average yet the peaks are high and might indeed burn things up. Sams is going to err on the cautious side. When I want to know what...
  4. RogerMod

    Power supply for two Mullard 5-10 amps

    The 10uF cap following the 10 K resistor might be your problem. Make that cap much bigger, like 100uF. We have bigger caps these days. Also be careful to adjust the screen resistor on the first tube to get the proper cathode voltage on the phase inverter. Typically I find 1/4 of the B+ should...
  5. RogerMod

    When we bias a tube amp what are we measuring?

    The plate cap on horizontal output tubes is for the high peak on retrace which can be many thousand volts (5000 typical rating). To make TVs reliable they just put on a plate cap, no big cost in that. The 807 has a plate cap more for keeping capacitance down at 30MHz in a transmitter. Though...
  6. RogerMod

    When we bias a tube amp what are we measuring?

    Here is the 807 data sheet showing 120 watts in an audio application which is ICAS (intermittant, not continuous full power, which is what we do in audio). It does require some grid drive power making it AB2. Granted the 807 is 5 watts more plate dissipation rating but I think this illustrates...
  7. RogerMod

    When we bias a tube amp what are we measuring?

    / While I agree it goes from 20 to 70 ma I do not agree with the rest. Have you tried this on the bench? I have. How much do you estimate the power loss to be? If there is no feedback the volume control will have to be turned down a few dB yet the power will be the same, only the gain...
  8. RogerMod

    Burning Amp 2018, Fort Mason, CA

    We had a nice turnout this October in San Francisco. Thanks to all the DIYers who brought their work to show off. Thanks to Linear Systems, makers of really low noise FETs and other SS devices, for hosting the event. Here is a link to their site. All the presentations can be seen there. See...
  9. RogerMod

    When we bias a tube amp what are we measuring?

    Excellent Question. Your edit correctly answers your question. It is indeed the dissipation of the chosen output tube that determines class A power in both single ended and PP amplifiers. The higher B+ brings many advantages the most of which is lower saturation voltage and greater swing...
  10. RogerMod

    When we bias a tube amp what are we measuring?

    When are we going to get a delete button for starting over? This is a bit frustrating.
  11. RogerMod

    When we bias a tube amp what are we measuring?

    You can get 100 watts from a pair of 6L6s, its on the GE data sheets. As for the RM-10 I gave a talk on that at Burning Amp 2018, just this month. Here is the link. The RM-10 amplication is near the end... I wanted to first have the audience understand a bit about data sheets. If you like put...
  12. RogerMod

    When we bias a tube amp what are we measuring?

    This is quite true and this I did to get the RM-10 to produce 40 watts from one pair of EL84/6BQ5s. The B+ is about twice the standard and the idle current is therefore half. The load is 14,000 ohms instead of the typical 8,000 ohms plate to plate. However to do this you must make the load...
  13. RogerMod

    When we bias a tube amp what are we measuring?

    Thanks to everyone for keeping this going and on topic. :)
  14. RogerMod

    When we bias a tube amp what are we measuring?

    If a tube biases at -15v and the target was -25 then you have a very weak tube. That is all. Throw it away.
  15. RogerMod

    When we bias a tube amp what are we measuring?

    Thanks, I wish all makers did this also. It is then much easier to see what effect regulation has on frequency response with impedance variations. We have to realize that Damping a woofer isn't everything, in fact, its the minor effect of the two. As Paul Klipsch said. Who cares about a ohm or...
  16. RogerMod

    When we bias a tube amp what are we measuring?

    Not at all. The bias point does not determine the gain nor the clipping point in a feedback amplifier. Are you considering that? Besides that large a change in bias voltage would typically create a 60 ma change in idle which is unreasonable. If already biased at 60 ma per tube now it is going to...
  17. RogerMod

    Good tube literature

    Excellent Book, and nicely done PDF. Here is a book worth studying. Its a wealth of practical information.
  18. RogerMod

    Good tube literature

    NIce to see the PDF is available. Thanks for the link. This book is a mix of information at many levels. Worth a look but dont get bogged down in the physics...unless you love that stuff. It is of the highest level written when the understanding and further development of vacuum tubes was at its...
  19. RogerMod

    When we bias a tube amp what are we measuring?

    Very good point and why we want matched tubes. Even with unmatched tubes and individual bias pots if the bias voltages are set quite differently as you describe there will be a problem of sharing current at full power Now this is a great reason for making the distinction between bias and idle...
  20. RogerMod

    When we bias a tube amp what are we measuring?

    Bias voltage has nothing to do with output swing as I have said before. Driver output determines swing. As long as the grid gets to zero volts in a AB1 amplifier that is full power. Mosty amplifiers achieve this with no problem. Please support your statement.
  21. RogerMod

    When we bias a tube amp what are we measuring?

    Hi triode. What you say in the first part is true if the driver is wimpy, like in the Stereo 70. The 7199 driver tube in that amp does not bias up uniformly from tube to tube. If you have more than about 105 volts on the cathode you will run out of drive and what you say will indeed happen. For...
  22. RogerMod

    When we bias a tube amp what are we measuring?

    I gave a talk yesterday at Burning Amp 2018. We had a audience of over 100 in the FIre House. Jim Tiemann, speaking for DIY audio made a passionate plea for those who can to help the new people learn about audio, proper thinking, and building their own stuff. This talk will be up in about 10...
  23. RogerMod

    When we bias a tube amp what are we measuring?

    I see your switches now and switching them out for their safety is a good idea. . They also provide a way to see when you leave class A. Nice touch. Also nice they say mA on them since that is what you are reading, the shunt is just elsewhere now. If it turned out that your original measuring...
  24. RogerMod

    When we bias a tube amp what are we measuring?

    I like your Sinatra quote, made me smile. What is a present wrench. did you mean preset? If so I would hand them a non adjustable wrench. :) I dont know of any single ended op amps, by definition op amps are differential otherwise they could not perform their "operations".
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