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  1. Replies
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    378

    From the descriptions of their web site I'd think...

    From the descriptions of their web site I'd think it was a YJS
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    378

    I don't know how accurate this is. It's all I...

    I don't know how accurate this is. It's all I could find.
    Looks like both the plate and screen voltage are reduced by 100V

    56280
  3. Thread: PCB manufacture

    by Dave H
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    189

    I've ordered a few from here - Quick-teck...

    I've ordered a few from here - Quick-teck and they were fine.
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    299

    What makes you think the OT is bad? The OT won't...

    What makes you think the OT is bad? The OT won't make the bias current rise. I'd suspect the control grid coupling capacitor. Short the control grid to ground. Does the bias current still rise? If...
  5. Yes, the two halves could be wired in parallel...

    Yes, the two halves could be wired in parallel but the gain increase won't be dramatic (only a few dB)
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    294

    Try running it up with the power tubes removed....

    Try running it up with the power tubes removed. If it runs up OK check the bias supply voltage.
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    433

    Yes, it's a musical 5th. If the root is C then...

    Yes, it's a musical 5th. If the root is C then it's G. Sorry for being so pedantic. I only know because I made the same mistake myself on this forum a while back. I used this table. C0 is 16.35. x 6...
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    433

    What note is the 6th harmonic? :)

    What note is the 6th harmonic? :)
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    433

    I'm not sure about that. I've just looked at a...

    I'm not sure about that. I've just looked at a table of note frequencies and it looks like this. 2nd harmonic is an octave, 3rd harmonic is a musical 5th (power chord interval), 4th harmonic is 2...
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    631

    Perhaps it's the EL34? You could try a 6V6...

    Perhaps it's the EL34? You could try a 6V6 without having to do too many mods. Increase the pi filter resistor R2 to 1k? to reduce B+ voltage and keep the 6V6 dissipation to less than 14W and set the...
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    1,011

    From the German for contact (Kontakt) perhaps?

    From the German for contact (Kontakt) perhaps?
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    936

    It has an extra gain stage but it only has a gain...

    It has an extra gain stage but it only has a gain of about 10 owing to its large unbypassed cathode resistor (R35) then most of that gain is dumped by the 3M3, 470k divider before the following...
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    936

    I meant that it's not as low gain as I first...

    I meant that it's not as low gain as I first thought because the two sections of the input trube (V5) are in series i.e. It has one more gain stage than the Top Boost pre-amp.

    I think the chain is...
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    936

    I don't think it has a lot of gain in the pre-amp...

    I don't think it has a lot of gain in the pre-amp before the master so there won't be much OD. (Assuming I'm looking at the right schematic). It's like a Top Boost circuit but with lower gain....
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    55876

    55876
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    267

    Test the temperature of each of the op-amps in...

    Test the temperature of each of the op-amps in turn with a finger. If one of them burns off your fingerprint replace it.
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    2,045

    I've seen it directly on the mains input for...

    I've seen it directly on the mains input for 115/230V selection.

    55837
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    55836

    55836
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    230

    Just speculating here - 66-135V is above the...

    Just speculating here -
    66-135V is above the neon maintaining voltage (50V) meaning the neon is always on so there's no trem.
    Closing the switch pulls the voltage down so that it's swinging above...
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    230

    It's OK to short it as there's a large resistor...

    It's OK to short it as there's a large resistor in series. I can't quite make it out but it looks like 300k.
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    It's a doubler but I think the bottom two diodes...

    It's a doubler but I think the bottom two diodes of the bridge are redundant. They will always be reverse biased.
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    The one on the right is a quadrupler (two stacked...

    The one on the right is a quadrupler (two stacked half wave doublers) :)
  23. To apply Ohm's law you need to use the voltage...

    To apply Ohm's law you need to use the voltage across the resistor not the B+ voltage. For the resistor feeding the PI and preamp tubes assume 1mA per dual triode. Four 12AX7s would be 8mA total. The...
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    722

    A series resistor doesn't load the voltage down....

    A series resistor doesn't load the voltage down. Imagine a 6V transformer winding driving a 5 ohm resistor. That's 1.2A from the winding. Now add a 1 ohm series resistor to make the load on the...
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    722

    If you just use two diodes in series it will only...

    If you just use two diodes in series it will only have half the waveform. It needs two more diodes in reverse parallel with the first two so now you have four diodes when one resistor would do.
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    572

    It's not normal as far as I know and they could...

    It's not normal as far as I know and they could have easily avoided it by changing the order of the series components.
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    752

    I prefer the JTM45ri circuit with the extra...

    I prefer the JTM45ri circuit with the extra resistor over your #2 circuit. The #2 circuit reverts to max bias current (-45V) when the wiper loses contact. The JTM45ri circuit reverts to min bias...
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    Edit: I don't like the one above. It's possible...

    Edit: I don't like the one above. It's possible to set the pot to zero bias voltage.

    Try this one.

    55528
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