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    What is pin 1 of IC4 doing? 54058

    What is pin 1 of IC4 doing?

    54058
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    I hate problems like that. You just don't know...

    I hate problems like that. You just don't know where to start!
  3. You should try measuring the ACV on the primary...

    You should try measuring the ACV on the primary first.
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    Sorry for slow response. Notifications are a...

    Sorry for slow response. Notifications are a feature of the site that could do with tweaking as they stop if you don't keep checking back to see what it happening.

    There is nothing magic about...
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    It works because the output impedance of the PI...

    It works because the output impedance of the PI and the MV pot form a potential divider, not due to mixing of phases.
  6. I'd say the most important reason for screen grid...

    I'd say the most important reason for screen grid resistors in the typical guitar amp is to avoid damage to the screen grid as a consequence of dissipating too much power. To small a value offers no...
  7. Dan argues that the monies received by the...

    Dan argues that the monies received by the foreign exporter end up back in the importer country so it has no net harmful effect (pg 5). What he fails to point out is that (a) this money is used at...
  8. True, but they still have to ship domestically...

    True, but they still have to ship domestically and do it for far less.
  9. ...and the 40W is $99.99! Not entirely...

    ...and the 40W is $99.99!

    Not entirely unrelated, I can buy single parts from China inc shipping for much less than the just the domestic shipping cost.
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    Lower the voltage to the screens and adjust bias...

    Lower the voltage to the screens and adjust bias to compensate will allow you to get just about any power out you want. I could give more detailed info but I'd need the schematic as I'm not sure...
  11. Sorry. I didn't get a chance to follow up on...

    Sorry. I didn't get a chance to follow up on this. The one I had is gone.
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    Not exactly since two of the old diodes are not...

    Not exactly since two of the old diodes are not used. I would leave the old diodes alone. Get two of the 1N4007's and connect in series. Solder that onto the end of one of the HT secondaries, anode...
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    Indeed it was a typo - Thanks.

    Indeed it was a typo - Thanks.
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    ..and what were the results of testing ZD1 (just...

    ..and what were the results of testing ZD1 (just remove it for a test) and not using a footswitch at all requested above?
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    That's the idea but see my addition abut the...

    That's the idea but see my addition abut the diode rating.
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    Revised version. Note you will have break into...

    Revised version. Note you will have break into the connection from the rectifiers to the filter caps in order to wire in the standby switch.

    53907

    PS: There's a further complication I just...
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    You MUST use the CT of the HT winding. You MUST...

    You MUST use the CT of the HT winding.
    You MUST NOT use th CT of the 6.3V winding.

    There is another wrinkle to to this that I thought of later. The standby switch is in the ground return path. ...
  18. The ripple is up to you. When you prototype the...

    The ripple is up to you. When you prototype the design you'll find out the hum level from the heaters. You can then adjust the filtering as you see fit based on your cost vs performance requirements.
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    The 2N3904 is only 40V whereas the original was...

    The 2N3904 is only 40V whereas the original was 100V.

    The two transistors in the one package have important properties of electrical and thermal matching. Therefore you should replace using...
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    2 x KSC1845 but you'll have to jiggle the leads a...

    2 x KSC1845 but you'll have to jiggle the leads a little.
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    I don't think that is right for the HT as it will...

    I don't think that is right for the HT as it will give you double the voltage. The BF uses a full wave rectifier while the RI uses a bridge. Therefore you will need to modify the bridge rectifier...
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    No, not amplified, but simply passing through the...

    No, not amplified, but simply passing through the speaker ( and OPT secondary) by means of the bad ground connection mentioned.
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    If you don't know what the cause was it's not...

    If you don't know what the cause was it's not really fixed. It wasn't the fuse for sure.

    With the standby off there are two circuits energized, the bias and the heater. The heater current to...
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    :thumbsup: Thx for schemo. TR3 is on sheet 13 top...

    :thumbsup: Thx for schemo. TR3 is on sheet 13 top right.
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    Need a schematic at least. The Service Documents...

    Need a schematic at least. The Service Documents on the web are of little technical value.

    The big question is why do you think you need to adjust it?
  26. 53879

    53879
  27. Any any difference in the voltage across the 3.9...

    Any any difference in the voltage across the 3.9 ohms resistors is primarily due to transistors differences. If a 3.9 was out of tolerance, the tube were different etc the idle current would be...
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    Are you using a footswitch? Try it without one....

    Are you using a footswitch? Try it without one. Does the one you are using have LEDS? The correct Marshall switch is PEDL-90004 which does not have LEDS on it.
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