1. Win a Broadcaster or one of 3 Teles! The annual Supporting Member Giveaway is on. To enter Click Here. To see all the prizes and full details Click Here. To view the thread about the giveaway Click Here.

Wire wound vs metal film resistors.

Discussion in 'Amp Tech Center' started by A13X, Jan 25, 2021.

  1. A13X

    A13X TDPRI Member

    Age:
    36
    Posts:
    44
    Joined:
    May 20, 2020
    Location:
    U.S.A.
    Hey all,

    I purchased a mod kit for a hot rod deluxe. They sent two metal film 5w 470 ohm resistors instead of the wire wound as pictured in the kit. If it's no big deal, I don't want to hassle the seller, but I was a little concerned as these two resistors seem to be a common point of failure (do to over heating) in this amp. I have some experience but not enough to know if my concern of heat, consistency, longevity, etc, justifies a request for a replacement.
    You're knowledge would be greatly appreciated. TIA
     
    Last edited: Jan 25, 2021
  2. Squawker

    Squawker Tele-Holic

    Posts:
    641
    Joined:
    Nov 1, 2017
    Location:
    Lommedalen, Norway
    5W max. power rating is what it is.

    Wirewounds are inductive (they're little coils), but metal film aren't. So they're "better" resistors. And if they're 5W rated then assume they can handle it as well as a 5W wirewound.

    It's called progress
     
    DeepDangler, DougM and A13X like this.
  3. A13X

    A13X TDPRI Member

    Age:
    36
    Posts:
    44
    Joined:
    May 20, 2020
    Location:
    U.S.A.
    Progress is what I hope I'm making in my journey to better understand electronics.

    Thank you for your reply and knowledge
     
  4. Dan_Pomykalski

    Dan_Pomykalski Tele-Meister

    Age:
    30
    Posts:
    364
    Joined:
    May 16, 2019
    Location:
    Madison, WI
    Good on you for doing your research before contacting the seller.

    You could always sent them a polite email asking them why the substitution though? You could also order the wirewound resistors yourself if you wanted to. I think those are like $1something from tubesandmore.com. You shouldn’t have to, but honestly that’s the route I’d go for least amount of hassle.

    As long as the rating’s the same though, I don’t think it’s a huge deal. Are these for grid stoppers?
     
    A13X likes this.
  5. Commodore 64

    Commodore 64 Friend of Leo's

    Age:
    45
    Posts:
    4,230
    Joined:
    Mar 1, 2010
    Location:
    Kent, OH
    Wirewounds have the least excess noise, but where you are putting them, and at the low ohms, it doesn't matter.
     
    schmee, A13X and DADGAD like this.
  6. A13X

    A13X TDPRI Member

    Age:
    36
    Posts:
    44
    Joined:
    May 20, 2020
    Location:
    U.S.A.
    As I understand it, these are the power supply resistors (does this mean they are grid stoppers?), they are also responsible for handling channel switching.

    I really just wanted to make sure there wasn't some reason that would make the wire wound critical in that location. The reason I'm replacing the original resistors is because EVERYTHING I have read on this amps says that they are mounted too close to the board...to be honest, the only changes I intend to make reliability mods. What seem to be considered the high rate of failure components. The tone mods I'll be holding off on for now.

    I just don't want to be 'That guy' . The PITA customer that doesn't know what he's talking about.
     
  7. A13X

    A13X TDPRI Member

    Age:
    36
    Posts:
    44
    Joined:
    May 20, 2020
    Location:
    U.S.A.
    For reference. 0B85B769-1CF0-4416-B983-55F8A254DE0A.jpeg
     
  8. Big-ez

    Big-ez TDPRI Member

    Age:
    52
    Posts:
    3
    Joined:
    Oct 8, 2020
    Location:
    Long Beach, LI
    They are totally fine. I’ve used both types. No difference in that application.
     
    A13X likes this.
  9. schmee

    schmee Doctor of Teleocity

    Posts:
    13,941
    Joined:
    Jun 2, 2003
    Location:
    northwest
    Those look like metal oxide not metal film and are great.
     
    A13X likes this.
  10. A13X

    A13X TDPRI Member

    Age:
    36
    Posts:
    44
    Joined:
    May 20, 2020
    Location:
    U.S.A.
    ‍ *face palm* now I'm that PITA forum poster that doesnt know what he's talking about.
     
    Dan_Pomykalski and Paul G. like this.
  11. schmee

    schmee Doctor of Teleocity

    Posts:
    13,941
    Joined:
    Jun 2, 2003
    Location:
    northwest
    haha... nah, just letting you know! They actually spec'd wire wound in the kit? Weird, you dont see those much anymore, never did in low values like that!
     
  12. Dan_Pomykalski

    Dan_Pomykalski Tele-Meister

    Age:
    30
    Posts:
    364
    Joined:
    May 16, 2019
    Location:
    Madison, WI
    Like the voltage dropping resistors between the filter caps? I’d think 5w metal oxide resistors would be perfectly fine there.
     
  13. Dan_Pomykalski

    Dan_Pomykalski Tele-Meister

    Age:
    30
    Posts:
    364
    Joined:
    May 16, 2019
    Location:
    Madison, WI
    I totally thought you said “metal oxide” in your original post.
     
  14. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

    Posts:
    2,883
    Joined:
    Dec 30, 2019
    Location:
    california
    As you have noted these get hot. Part of the problem with the HRD is these resistors get hot enough to compromise the solder joint and solder pads of the PCB. When you install these resistors make sure they are not touching the board. Give them a little air space. The leads of the resistor can be left long. The extra lead length will act as a heat sink to help keep the solder joint cooler. There is plenty of space behind the board for the long leads so why not.

    The CR13 CR14 16v Zener diodes associated with the 470R resistors could also be raised from the board for heat reasons.

    Also be very careful when removing the original resistors. Do not damage the solder pad of the PCB. I would cut the old resistor out, then remove the small bit of lead.
     
    Last edited: Jan 26, 2021
    J-Flanders and hepular like this.
  15. A13X

    A13X TDPRI Member

    Age:
    36
    Posts:
    44
    Joined:
    May 20, 2020
    Location:
    U.S.A.
    Thank you so much for the tips!!

    I have read that some people place some sort of ceramic spacer to hold them off the board. Do you believe this is necessary, or would it be just fine to space them without the ceramic?
     
  16. DeepDangler

    DeepDangler Tele-Meister

    Age:
    30
    Posts:
    349
    Joined:
    Sep 28, 2020
    Location:
    Mequon, WI
    Make sure to get the solder removal tool as well. It will help you keep the area clean when before you put the new resistor in.
     
    A13X likes this.
  17. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

    Posts:
    2,883
    Joined:
    Dec 30, 2019
    Location:
    california
    I have used the old ceramic box resistor as a standoff. I make sure the leads can't touch. I use silicon goo to stick the old resistor to the PCB. The resistors don't weigh too much so they don't need a standoff ime. Your choice.

    (A silicon for electrical devices should be used if a silicon is to be used.)
     
    A13X likes this.
  18. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

    Posts:
    2,883
    Joined:
    Dec 30, 2019
    Location:
    california
    Measure the resistance on the new resistors.

    Sorry if my monitor is displaying the colors wrong.
     
    A13X likes this.
  19. A13X

    A13X TDPRI Member

    Age:
    36
    Posts:
    44
    Joined:
    May 20, 2020
    Location:
    U.S.A.
    My fluke is somewhat out of calibration for some reason. It will read 13.5 probe to probe. When checking resistance on a couple speakers recently I confirmed that that it was infact off by that 13.5 regardless of what I'm measuring. Anyway, they read 470 and 469.5 so I presume they both check out at about 456.
     
    Lowerleftcoast likes this.
  20. A13X

    A13X TDPRI Member

    Age:
    36
    Posts:
    44
    Joined:
    May 20, 2020
    Location:
    U.S.A.
    I picked up some solder wick and a suction bulb, I have very little experience de-soldering. I've watched a ton of videos on it and I'm gonna practice a bit on a dead PC board I have.. crossing my fingers this goes well.
     
    DeepDangler likes this.
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.