NFB Resistor's wattage????

Discussion in 'Amp Tech Center' started by Rod Parsons, Jan 2, 2018.

  1. Rod Parsons

    Rod Parsons Friend of Leo's

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    I have just purchased a new 5 watt, class A, all tube amp for my grandson, at an amazing, [to me], price.. I went to YouTube and found out more about it. One guy explained how the 'stock' 220 ohm resistor in the negative feedback loop is way too small. He suggests a resistor value between 20K to 30K to give the amp more punch... Or to put a 50K Ohm Pot in it and adjust it anytime to where it sounds best.. I want to try one of these, but the guy, demonstrating where in the amp, and how to do it, didn't mention the wattage value needed.. Is one watt about right? Or do I need more or less than that? Thanks!
     
    Last edited: Jan 2, 2018
  2. Phrygian77

    Phrygian77 Tele-Afflicted

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    1/2 or higher should be sufficient. There are really two NFB resistors (sometimes one is also a cathode resistor) that create a voltage divider. 2k to 20k or higher is big change. What amp are we talking about here?
     
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  3. Rod Parsons

    Rod Parsons Friend of Leo's

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    Sorry! I just went back to the utube video and realized, that it was a 220 Ohm resister,... not 2K Ohm. He showed a close-up of the resister he removed... sure enough...220 Ohms. The amp is a 'Monoprice' #611705,,... 5 watt, one 8 inch speaker,,... with one 12ax7 and one 6V6,.. diode rectified. According to the utube video, it is the san\me amp as was the Laney Cub Eight... Monoprice has it's own web sight and they sell cheaper than anyone I could find.. $90.00 free delivery with today's 10% off sale.. The reviews are awesome.. I may get one for myself..
     
    Last edited: Jan 2, 2018
  4. LudwigvonBirk

    LudwigvonBirk Tele-Holic

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    agreed
     
  5. Phrygian77

    Phrygian77 Tele-Afflicted

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    I couldn't find a legitimate schematic or layout for that amp. I found someone's hand drawn layout/schematic, but I'm fairly certain, after looking over it, that it has errors. It looks like the NFB resistor is 33k, which connects to the pin 3 (cathode) of V1.

    [​IMG]
     
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