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  1. Replies
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    Please consider for a moment what the load on a...

    Please consider for a moment what the load on a guitar amplifier power transformer actually looks like. The previous discussion seems to assume the transformer is used at max rating all the time. In...
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    To clear up any confusion; Vertical type...

    To clear up any confusion;

    Vertical type MOSFETs like the IRF 'HEXFET' types have the Drain connected to the case or heatsink tab. I'm not aware of any exceptions.

    Some but not all Lateral Type...
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    It's good that you kept those manuals. In most of...

    It's good that you kept those manuals. In most of the industrial settings where I've been employed, they just get lost or thrown away along with any spare tips that came with the probes. Then, when...
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    Those tips are usually specific to one or a...

    Those tips are usually specific to one or a narrow range of probes. Your only hope is to contact your local Tektronix Field Office. Most of the older Tek manuals can be found on ebay. If you can't...
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    Unless you really need the form factor or...

    Unless you really need the form factor or portability, it's twice as expensive as what is needed for work on guitar amps. It's new with a warranty and that's worth something, but used scopes are...
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    I remember a version of the Blackface Bassman...

    I remember a version of the Blackface Bassman that only used half a 12AX7, they only connected the heater on the side that was being used. In your case that would be pin 5 not connected.
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    I just fired up my 2203 clone and the Voltage at...

    I just fired up my 2203 clone and the Voltage at pin 1 (the schematic you posted) of V2 was 285V. That's in the ballpark of what you find on most of the Marshall Voltage charts. Highest I found was...
  8. When you say 6 to 8 12AX7 tubes, do you mean 12...

    When you say 6 to 8 12AX7 tubes, do you mean 12 to 16 triodes, or just 6 to 8 triodes ?
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    428

    You don't need the part that includes R30 and D1....

    You don't need the part that includes R30 and D1. You don't really need the part that includes C20 and C21, except that your power supply will need some kind of filter, just not as big as the one...
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    Some Boss pedals were originally designed to run...

    Some Boss pedals were originally designed to run from a slightly hummy Boss unregulated 12V wall wart. They have additional filtering that drops the voltage from the external supply jack and lowers...
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    My experience tells me that you have to be very...

    My experience tells me that you have to be very careful with grounds on the output of some switching supplies. An additional stage of L-C filtering on the output might be appropriate. Does the little...
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    That ground on the Mains input is important for...

    That ground on the Mains input is important for EMC suppression. No way the supply could meet EMC specs without it.

    In the USA, Dell is a big name in personal computers. When they started out in a...
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    For small values, try to find an NPO temperature...

    For small values, try to find an NPO temperature rating.
  14. Yes, you can use the bias tap as long as you...

    Yes, you can use the bias tap as long as you don't need too much current. One problem is dealing with the Voltage that might be +/- 60V. Most solid state regulators can't deal with that. Zener diodes...
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    1,950

    Isn't crest factor just Peak/RMS ? In the first...

    Isn't crest factor just Peak/RMS ? In the first example it looks like the crest factor is just less than 3. T1 peak current 1.7697A, RMS .61188A . The assumption is that the numbers for the...
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    The schematic is posted in this thread:...

    The schematic is posted in this thread: https://music-electronics-forum.com/showthread.php?t=32812

    The layout for channel 1 preamp is in post 7 of this thread:...
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    Make sure those 8x10 cabs are firing on all 8...

    Make sure those 8x10 cabs are firing on all 8 cylinders.
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    The YBA-1A's prior to 1970 had huge output...

    The YBA-1A's prior to 1970 had huge output transformers. Normally they only used the 8 Ohm tap, if you take off the end bell, there is a 16 Ohm tap wire that is cut short.
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    If you really gotta know, 4 wire measurements...

    If you really gotta know,

    4 wire measurements to the black common wire (no averaging):

    4 Ohm tap, 0.36390
    8 Ohm tap, 0.48331
    16 Ohm tap, 0.71211 (1047 Ohm feedback network in parallel)
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    I just took resistance readings on a Dynaco 40W...

    I just took resistance readings on a Dynaco 40W amp that sits near my computer as a chrome monument. Plate to plate, 185 Ohms. One side to center tap, plate 102.4 Ohms, screen 34.2 Ohms. Other side,...
  21. In the Dallas area we are blessed with one of the...

    In the Dallas area we are blessed with one of the best "surplus" electronics stores anywhere. It started out in the late 70's almost exclusively surplus electronics from local companies going out of...
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    It's not an issue yet, but when one of those...

    It's not an issue yet, but when one of those little computers in your car fails, you might not be able to get a new or rebuilt one from the manufacturer. Even if you could find one at a wrecking...
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    What type of impedance switch does this amp have...

    What type of impedance switch does this amp have ? Is it the same kind of PCB mount slide switch that Marshall uses on the back of speaker cabinets that allows the 4x12 to be split into stereo ?
    ...
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    This amp has no short circuit or over current...

    This amp has no short circuit or over current protection other than the fuse on the output. Amps like this typically don't have an extension speaker jack. It's designed to run the internal speaker...
  25. I always thought the 5AR4/GZ34 had controlled...

    I always thought the 5AR4/GZ34 had controlled warm up but looking at the RCA data sheet I'm not seeing any reference to that.
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    It's all relative. A really long time constant...

    It's all relative. A really long time constant might seem like forever, but it's not. Any decent modeling program will show you that the capacitor is still blocking DC or holding the DC up. Like the...
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    Could the pins of Q8 be scrambled ? Could the...

    Could the pins of Q8 be scrambled ? Could the Base and Emitter be reversed ? What is that note in the lower left corner of the schematic ? Shouldn't the pinout be B C E if you are looking at the top...
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    Back in the day, Tektronix made a special scope...

    Back in the day, Tektronix made a special scope called the 570. Using it you could display the plate current curves of many tubes. Connections to the tube socket were made by short jumper wires. When...
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