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    Its not necessary. A 1N4007 works perfectly.

    Its not necessary. A 1N4007 works perfectly.
  2. Look here: http://www.pedrovecino.com/JCA20H.pdf

    Look here: http://www.pedrovecino.com/JCA20H.pdf
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    Yes. It appears in the schematics of M. Huss. ...

    Yes. It appears in the schematics of M. Huss.

    54218

    The voltage doubler is only essential in the DR103 (100 watts). Although it also serves the system that Marshall uses in the JCM900. The...
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    I dont know if I understood correctly but the...

    I dont know if I understood correctly but the DR504 does not need a voltage doubler. Its enough to extend the voltage divider to the good side with an adjustable resistor. It's the DR103 that needs...
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    Ive already done the tests. I started by...

    Ive already done the tests. I started by lowering the resistor from 10K to 3K2 to test. The hum was raised appreciably. Then I tried with 5K and to eliminate the hum I added 10uF in the second node...
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    Yes, I thought first that I would need to...

    Yes, I thought first that I would need to accommodate the cathode resistor value in the power tubes when making that change, but I'm sure more things will be necessary. Dave talked about "stiffish...
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    Yes, that is exactly. I have not measured the...

    Yes, that is exactly.
    I have not measured the power, but by ear is It's similar or slightly smaller than a single ended with EL84 and 260V. Its consistent with those 4.5 watts.



    Tomorrow I...
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    Thanks! The problem is not in the gain of the...

    Thanks! The problem is not in the gain of the circuit around 6SJ7, I think. I also tried connecting in triode mode, with G2, G3 and the plate attached. Basically the volume/distortion obtained with...
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    I did it through an aerial miniswitch but without...

    I did it through an aerial miniswitch but without results. It sounds exactly the same. I also tried to raise the value of the cathode resistor and effectively lowered its gain but the overdrive ratio...
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    Thank you. Do you mean install an electrolytic...

    Thank you. Do you mean install an electrolytic capacitor in parallel with the cathode resistor or to use individual resistors on each cathode?
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    Volume transition between 0 and 3 is fine. It's...

    Volume transition between 0 and 3 is fine. It's really good on the whole scale. The problem is that above 3 the distortion appears prematurely in relation to the volume.
    A good 5E3 or 5C3 has a much...
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    I'll keep it in mind. Thanks!

    I'll keep it in mind. Thanks!
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    A moment ago, before reading your comment I...

    A moment ago, before reading your comment I replaced the 220K plate resistor by 47K to see what happens. I have done it on one of the 6SJ7 inputs that already has a cathode bias circuit and that...
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    Well, I have it already working. It has dimension...

    Well, I have it already working. It has dimension and a nice compression but its clean sound threshold is very small.
    I have put the voltages I get.
    It is equipped with a 5Y3 RCA and I get 290V....
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    I will keep it that way. Danke, Helmholtz.

    I will keep it that way.

    Danke, Helmholtz.
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    Strange wiring in Gibson GA-20

    Hi all. I have a Gibson GA20 that was previously treated (change of coupling and filtering capacitors) in which I have seen something strange: the feed line to the PI is taken directly from the...
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    54042 Be careful with the contamination in...

    54042

    Be careful with the contamination in that area. From left to right:
    D12 - diode between EL84 plate and ground.
    R34 - input grid resistor
    R36 - screen grid resistor
    R32/31 - bias feed...
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    I only use it on Vox type amplifiers. I usually...

    I only use it on Vox type amplifiers. I usually install a limiting resistor in series to establish margins for good operation. That way nobody can say "it sounds really bad with the master volume at...
  19. They are not used.

    They are not used.
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    Is it a 5F8A? In the Bassman 5F6A a conventional...

    Is it a 5F8A? In the Bassman 5F6A a conventional master volume after the treble control works very well. A suitable place is on one of the inputs of the normal channel.
  21. A curiosity: the original power transformer (at...

    A curiosity: the original power transformer (at least here in Europe) has an internal fuse. The good thing is that it has the two points accessible from the outside.
    Once I found one completely...
  22. Grid resistors in each triode are associated with...

    Grid resistors in each triode are associated with the incorporation of the two modules that replace the neon/LDR. This happens in all since they started installing it eleven years ago.
    Have you...
  23. Could it be related to a problem around D6, D7,...

    Could it be related to a problem around D6, D7, R36 and C16? (The group of components between the star earth and chassis)
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    I dont know if I have understood it well, but...

    I dont know if I have understood it well, but the voltage in the first and second filter capacitor should be between 425 and 440 volts approximately.
    Visually check if some of the surface mounted*...
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    It certainly requires an appropriate work bench...

    It certainly requires an appropriate work bench ;)

    53790
  26. Ok. TAD supplies in two different ways: one of...

    Ok. TAD supplies in two different ways: one of them is labeled with the relative plate current (PC) and transconductance (orange boxes) and the other simply shows the mark and a number between 1 and...
  27. Which are the EL84 TAD Shuguang? The Chinese EL84...

    Which are the EL84 TAD Shuguang? The Chinese EL84 TADs are the STRs.
    I imagine that if they are Chinese they must be the same.
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    Sorry. My English is very bad (I dont ...

    Sorry. My English is very bad (I dont understand how I have not been kicked out yet). I was trying to say that in my opinion on a basically clean amp the existence of a loop is not very useful...
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