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  1. Replies
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    790

    The simulation below says you are correct...

    The simulation below says you are correct :thumbsup:
    Blue is bias voltage, Red is grid signal, Green is output (8 ohms)
    At clipping the peak grid drive is equal to the bias voltage.

    54080
  2. Replies
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    790

    This is straight from pedant's corner :) The...

    This is straight from pedant's corner :)

    The average value of any number of whole sine waves is zero.
    The average value of the positive half of a sine wave is Vp*2/pi
    The average value of the...
  3. I've assembled a few transformers. Stacking the...

    I've assembled a few transformers. Stacking the laminations was easy enough except for the last few which required a bit of wiggling and some persuasion with a rubber mallet. Make sure you take note...
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    790

    :confused: Are you sure, isn't that average...

    :confused: Are you sure, isn't that average power?
    RMS power would be the RMS value of the power waveform which isn't useful.
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    790

    True, that's why I said average power in post #19...

    True, that's why I said average power in post #19 :)
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    790

    Yes, that's what I thought. When I use the...

    Yes, that's what I thought. When I use the approximation formula on my 15W EL84 amp it give the output as 33W.
  7. Replies
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    790

    The bias voltage is the peak voltage isn't it?...

    The bias voltage is the peak voltage isn't it? That's what I was thinking about. Peak to peak is twice the bias voltage.
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    I think there's 4V on the collector because it's...

    I think there's 4V on the collector because it's trying to turn on the non existing Q303 to bring the output voltage down. Where is the output sitting with Q303 out? It should be high (~90V) if it's...
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    Doesn't that give peak power as gm*Vg is peak...

    Doesn't that give peak power as gm*Vg is peak current?
    Average power will be half of that.
  10. Replies
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    Good plan, I'd also check C308 for leakage. With...

    Good plan, I'd also check C308 for leakage. With the base voltages you have on the LTP Q301 should be off and Q302 should be on. Is the collector of Q301 at 0V and the collector of Q302 at 8V? That...
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    Yeah, but the output impedance of the usual LTP...

    Yeah, but the output impedance of the usual LTP PI is only around 40K so the PI 'wins' :)
    A 40k resistor to ground from each output of the PI would divide the signal by two as would an 80k between...
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    Are the base voltages the same on the...

    Are the base voltages the same on the differential pair? The output voltage should be roughly 4 x the voltage on Q301 base. Can R304 be adjusted to set 11V on C304 + (and Q301 base)? If it won't go...
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    Here's the schematic I have. It should work...

    Here's the schematic I have. It should work without the missing parts. As the output is sitting between the rails I'd suspect the LTP transistors. Will R304 adjust the output voltage?

    53993
  14. You could have saved time by first checking with...

    You could have saved time by first checking with a DMM to see if the mystery wire was grounded ;)

    For it to have negative feedback there would need to be two extra wires, one to ground one side of...
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    Even with a tube rectifier there's still the turn...

    Even with a tube rectifier there's still the turn on surge of the transformer and heaters.
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    Looks great from 4400 miles away :)

    Looks great from 4400 miles away :)
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    53870

    53870
  18. Sticky: You should really swap the OT leads but for a...

    You should really swap the OT leads but for a quick test try disconnecting the negative feedback wire at the board. It's the right hand end of the red wire on Chuck's marked up layout.
  19. 53858

    53858
  20. I don't think a shorted C7 could burn out the...

    I don't think a shorted C7 could burn out the resistors because there would still be R111 100k in series to B++ Perhaps there was a short from grid to plate or screen in either V5 or V7 then the...
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    What is the input connected to? If it's DC...

    What is the input connected to? If it's DC coupled to a low impedance source the op-amp will have a gain of 48 to its own input offset voltage which will turn a 4mV input offset voltage to 200mV at...
  22. Thread: soldering irons

    by Dave H
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    I bet it's not as old as mine. I've been using it...

    I bet it's not as old as mine. I've been using it for decades.

    53721

    No wait that was my dad's.
    This is like mine but mine has a black base unit.
    It's temperature controlled by tip selection...
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    The EL84 data sheet doesn't have plots for a Va...

    The EL84 data sheet doesn't have plots for a Va and Vs of 190V so some interpolation is necessary.

    I'm guessing the peak voltage available will only be about 160V. If the OT is 5k then peak (bias)...
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    What is the impedance of your output transformer?

    What is the impedance of your output transformer?
  25. I don't think 9V rms is enough to generate 12.6V...

    I don't think 9V rms is enough to generate 12.6V DC. I'd run it through PSUD2 to check.
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    I'd pull the PI tube before turning the amp on.

    I'd pull the PI tube before turning the amp on.
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    You could think of impedance as resistance to...

    You could think of impedance as resistance to Alternating Current (AC)

    Edit: I see Helmholtz has already said that :)
  28. If this is the correct schematic and PCB layout...

    If this is the correct schematic and PCB layout it looks like a really messy mod to do. All the pin 8s are connected together and pin 3 is connected through pin 1

    53699

    Edit:
    I see we have...
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