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    Yes, see posts # 11,17, 26.

    Yes, see posts # 11,17, 26.
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    A DCR difference between primary halves of up to...

    A DCR difference between primary halves of up to 20% is not unusual (depending on winding/interleaving scheme). But the AC voltages on both halves must be identical.
  3. I was there amongst around 600,000, saw the...

    I was there amongst around 600,000, saw the concert and was overwhelmed by the sheer power of the Who. I always thought they were the most dynamic and powerful rockband I ever saw. The only other...
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    I would - make sure that the speaker out...

    I would
    - make sure that the speaker out switching jacks work properly
    - disconnect all OT leads and do a neon bulb test.
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    Bottom line is that a PT that gets too hot even...

    Bottom line is that a PT that gets too hot even without a load should be replaced because it is a potential safety risk. Even more alarming if it ran cooler before, as that means that something...
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    Yes, thanks.

    Yes, thanks.
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    Not really necessary, at least it won't give me...

    Not really necessary, at least it won't give me additional information.

    Ghost notes (= intermodulation distortion) mean that some residual hum or ripple mixes up with your guitar signal. Without a...
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    That may well be. My comment was meant to...

    That may well be.
    My comment was meant to support the statement that taper will change and no longer be linear with a parallel resistor. In fact resulting resistance will change faster in the lower...
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    Assuming the presence works as intended, the...

    Assuming the presence works as intended, the position of the presence pot does not actually change plate voltages, it just changes the amount and phase of HF NFB, thus influencing stabilty conditions...
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    Not quite. A linear 50k pot with the wiper tied...

    Not quite. A linear 50k pot with the wiper tied to the end gives 25k in middle position. A linear 100k pot in middle position paralled with a 100k resistor means 50k parallel to 100k resulting in...
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    Look at it this way: If the voltage drop of...

    Look at it this way:

    If the voltage drop of 30V across a primary half was caused by high idle (DC) plate current, this would mean a total current of 1.77A and a dissipation of 866W for the 2 tubes...
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    No I meant plates. Power tube plates are the...

    No I meant plates. Power tube plates are the highest gain and amplitude "outputs" of a tube amp. Connecting a long lead to them produces a transmitting antenna.
    The oscillation eats power and thus...
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    I think you are triggering a power amp HF...

    I think you are triggering a power amp HF oscillation when touching the plates with your meter probe. Symptoms are typical: lowered DCV reading and humming.
    The meter lead causes a positive feedback...
  14. Thread: Pickup dying

    by Helmholtz
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    So you were lucky and I hope you can preserve...

    So you were lucky and I hope you can preserve this condition. (BTW, are you sure the previous value of 140k was real and you did not touch the probe tips with your fingers while measuring?)
    ...
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    Shorted turns should show in the neon bulb test...

    Shorted turns should show in the neon bulb test and would most probably cause way higher input current.

    I think it's just a poor transformer design with relatively high magnetizing current. This...
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    At 120V that means an apparent input power of...

    At 120V that means an apparent input power of 11.2W, which is quite a lot for a small transformer (what are the core dimensions?). Unfortunately without a "Kill a Watt" we don't know the percentage...
  17. Thread: Pickup dying

    by Helmholtz
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    If just one wire turn contacts a magnet, PU sound...

    If just one wire turn contacts a magnet, PU sound won't change. It requires more than one turn contacting the same magnet to produce some detrimental effect.

    Corrosion typically requires some...
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    What matters regarding transformer heating is...

    What matters regarding transformer heating is primary current.

    Please measure with and without secondary load.

    Do you have a "Kill a Watt" meter that reads real input power?
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    Sticky: Not sure if I understand. Can you show your...

    Not sure if I understand. Can you show your circuit?

    I would wire additional resonance shaping RC components in parallel to the series arrangement of PU+ secondary of CT (and not across the PU...
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    Not sure but maybe you didn't encounter grid...

    Not sure but maybe you didn't encounter grid conduction with pentodes. Pentodes have higher gain and thus require less grid drive to be driven into (smoother) plate saturation.
    Also pentodes have...
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    It happens because the grid-cathode path acts...

    It happens because the grid-cathode path acts like a diode. As soon as the grid gets more positive than the cathode, the diode is forward biased and starts conducting current. This in turns loads...
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    This means you will get clipping by grid...

    This means you will get clipping by grid conduction as soon as the grid signal amplitude exceeds +43V.
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    Sticky: Then your loop area needs to be at least 4 times...

    Then your loop area needs to be at least 4 times larger than the PU coil area (with 2 turns).
    I don't have a proof but assume that the alnico magnets somewhat increase the hum field in the PU, maybe...
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    Sticky: Beautiful and extravagant instrument! ...

    Beautiful and extravagant instrument!



    Does the PU only have 1100 turns? In this case the loop area doesn't need to be much larger than the PU coil area using 2 turns and a 1:500 CT.( My...
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    I suspect EL34 grid conduction, meaning that grid...

    I suspect EL34 grid conduction, meaning that grid drive voltage is too high for the circuit. This would show in clipping of the positive peak of each PI output.

    What is your bias voltage?
    Can you...
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    Sticky: I am tired now, but my preliminary evaluation...

    I am tired now, but my preliminary evaluation would be this:

    3 primary turns will triple induced primary voltage. Transformer step-up ratio is determined by the ratio of secondary to primary...
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    Sticky: Sounds like an excellent idea! A larger loop...

    Sounds like an excellent idea!

    A larger loop area will produce more signal and will reduce step-up requirement (number of CT turns) and/or will allow fine tuning with resistors. As always loop...
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    But that means that you could achieve signal...

    But that means that you could achieve signal symmetry with your circuit. Now I don't understand your problem.

    Also consider that the 2 triode systems may easily differ by 10% or more.


    BTW,...
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