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  1. Replies
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    And one of these. 54379

    And one of these.

    54379
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    How effective is the 500k tone pot across the 43R...

    How effective is the 500k tone pot across the 43R cathode resistor?
    I wouldn't think it would have any effect until it hit the CW end stop.
  3. The way it's drawn is a bit confusing but as Enzo...

    The way it's drawn is a bit confusing but as Enzo says it's a gain stage followed by a cathodyne PI (similar to the 5E3).

    I think you've landed on a good value for the bypass cap. On the plot...
  4. Too easy :)

    Too easy :)
  5. I'd try connecting a resistor in parallel with...

    I'd try connecting a resistor in parallel with the gain pot VR6
    Gain reduction would be 15dB using 100k, 20dB using 56k.

    Both sides of the pot are at ground potential so there shouldn't be any...
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    Looking at the picture it could be a funny Q as...

    Looking at the picture it could be a funny Q as it's not the same as the 8 above it.
    It should measure DC there. I suppose you've checked the fuse? ;)
    Do the diodes measure OK in the C4P03 thingy ?...
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    It looks like C4P03Q on the schematic which is a...

    It looks like C4P03Q on the schematic which is a dual Schottky rectifier - 54346

    Where exactly are you measuring?
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    Typo, that should read centre tap to pin 2

    Typo, that should read centre tap to pin 2
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    500V across 440k is just over 1mA. The PT won't...

    500V across 440k is just over 1mA. The PT won't notice that.

    The value of the balance resistors is chosen to make the current through them much greater than the capacitor leakage current. If the...
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    It's a full wave rectifier. It needs a centre...

    It's a full wave rectifier. It needs a centre tapped transformer winding. Something like 7-0-7 volts should do it (as the input capacitors look to be only rated at 10V). Connect the ends of the...
  11. Is 350V the plate voltage or B+ voltage? I think...

    Is 350V the plate voltage or B+ voltage?
    I think you've subtracted the OT voltage drop from the plate voltage but it's the cathode voltage which should be subtracted as you need to know the cathode...
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    I've been thinking about this :confused: And I...

    I've been thinking about this :confused:
    And I think it goes like this -

    The 220k balancing resistors will divide the voltage equally for the DC steady state condition.

    For the switch on state...
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    You don't need to be an engineer :) Without...

    You don't need to be an engineer :)

    Without balancing resistors the capacitors would share the (DC) voltage according to their leakage currents, the capacitor with the larger leakage current...
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    I think we are both right :) I said if one...

    I think we are both right :)

    I said if one tube is not conducting then the OTHER red plates.
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    If one tube has no plate current the other tube...

    If one tube has no plate current the other tube will most likely red plate because they share a common cathode resistor. This could also happen if one side of the OT primary failed open but both...
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    Which sadly won't fix the problem :(

    Which sadly won't fix the problem :(
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    Right, so it doesn't have a loud enough clean...

    Right, so it doesn't have a loud enough clean sound?
    Have you measured the clean output power?
    A 290V supply is a lot lower than a 5E3.

    I ran a similar output stage through LTSpice with a...
  18. Thread: 6P14P-K

    by Dave H
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    Here's an English data sheet. It says Pa max for...

    Here's an English data sheet. It says Pa max for 6P14P is 14W and it's also rated at a higher max voltage than EL84.

    54169
  19. Yes, good point!

    Yes, good point!
  20. It's most likely because pin 4 is open circuit...

    It's most likely because pin 4 is open circuit from ground/battery negative. With the battery disconnected check for continuity between battery clip -ve and pin 4. If it isn't a very low resistance...
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    If it's clean at low vol pot settings (no first...

    If it's clean at low vol pot settings (no first stage distortion) but distorts as soon as it's turned much above '1' then it could be the back to front quick start 5E3 style vol pot wiring. The vol...
  22. The dual gang pot P2 adjusts the signal level of...

    The dual gang pot P2 adjusts the signal level of the effects loop but the loop is unity gain send to receive because as the gain of the send amp is increased the gain of the receive amp is reduced.
    ...
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    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
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    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...
  25. 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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    :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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    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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    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.
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