What is this resistor in my Deluxe Reverb?

Discussion in 'Amp Tech Center' started by beyer160, Dec 13, 2019.

  1. beyer160

    beyer160 Friend of Leo's

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    I opened up my 1980 Deluxe Reverb tonight, in order to troubleshoot the trem intensity (you don't start hearing anything until the intensity is at about 5. It's not a huge deal, I just wanted to see if I could do anything with it). While I was in there, I noticed this-

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    It's a 200 ohm resistor (Clarostat VC5E 200), about 5 watts if my research is correct. It's on the B+ line between pin 8 of the rectifier and the circuit board. It's not on any of the AB763 schematics I've seen. Any idea what it's for?
     
  2. Dacious

    Dacious Poster Extraordinaire

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    Voltage dropper. Seems overkill at 5watts for 200 ohms, that's going to be small drop. Or - someone is trying to emulate rectifier sag.

    Possibly someone who worked on the amp in the past was a bit anal about things being 'just so'. They didn't like the B+ being higher than spec.
     
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  3. Wally

    Wally Telefied Ad Free Member

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    If you are curious, take the voltage measurements from both ends of that resistor.
     
  4. slider313

    slider313 Tele-Afflicted

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    I'd be more concerned with the wire nuts on the power transformer lines...........:eek:
     
  5. CWP0126

    CWP0126 Tele-Meister

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    Hi @beyer160 ,

    I have a 1980 DR too, and I think those have a slightly different circuit from the AB763. When I got mine I saw that resistor too, and I searched for gut pics of late 70s DRs and saw it on enough of them to convince me that it was a factory component. Here are a few pictures of the one in mine, which I think is original judging by the others I saw because of its size, shape, and color. Yours looks different, but I’m not saying it isn’t original, I have no idea on that.

    The wiring in yours looks a lot cleaner than mine, despite the wire nuts. Yours has more cloth covered wires too, mine has mainly plastic wiring.

    As you can see this amp has a replacement PT that decodes to one out of a DRRI. It’s a shame they had to hack the chassis to fit it in there, but whatever, it sounds good and works fine. It’s been my favorite amp since I got it!


    5C25953F-4771-4F78-BF56-5F8238F799B1.jpeg 7638AD8F-731C-4B11-8BD3-E79AA1B97AA7.jpeg 00257D24-1A99-4530-80F4-145B4F3D0D1B.jpeg
     
  6. milocj

    milocj Friend of Leo's Ad Free Member

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    Aren't those thermistors that Fender added to the later 6V6 models? I'm pretty sure I remember seeing those on schematics for a PR and DR with the boost function that I worked on in the past.
     
  7. Andy B

    Andy B Friend of Leo's Silver Supporter

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    In the last 2 pictures above, if my eyes aren't deceiving me, that is the "death cap". The white wire appears to go to the center of the ground switch while the other side of the cap is tied to the center lug which is chassis ground.
    The OP's picture shows a dropping resistor of some sort which was probably installed when the transformer was replaced IMHO.
     
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  8. Wally

    Wally Telefied Ad Free Member

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    CWP0126, that blue cap in your amp is not what is sitting in beyer’s amp.....totally different component and situation.
     
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  9. DADGAD

    DADGAD Friend of Leo's

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    A voltage dropping resistor. Could have been added so that a solid state rectifier could be used instead of a 5U4. Or, the previous owner wanted more sag.
     
  10. CWP0126

    CWP0126 Tele-Meister

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    Good to know, thanks Andy and Wally for setting me straight!

    If it's the death cap, should I leave it in there or take it out? The amp does have a 3 prong grounded plug and a ground switch. I never touch the ground switch, it has a middle position that says "off" and that's where it stays.

    IMG_1970.JPG
     
  11. Wally

    Wally Telefied Ad Free Member

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    CWP0126, when I start looking at that death cap, I start looking at all of the AC power in wiring. If you do your own tech work, there are changes you could make. If not, a tech would know what needs to be done there. I am going to think that the white neutral is traveling to a fuse and then to the PT primary while the hot black wire is going through the power switch. If so, there is a better and safer way to do that.
     
  12. Andy B

    Andy B Friend of Leo's Silver Supporter

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    I’d disconnect it. It serves no purpose with a 3 wire grounded AC line.
     
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