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old Randall RPM300 power amp

Discussion in 'Amps and Cabs [BG]' started by jjhardy, Jun 28, 2008.

  1. Jun 28, 2008 #1
    jjhardy

    jjhardy

    Mar 11, 2007
    found one of these for $10, and much to my surprise it seems to work. a few questions for those who can answer:


    how many watts does this push at 4 ohms? it does 500 at 2 ohms, so i figure about 300 at 4 sounds right, but i'd like to know the exact.

    it makes a lot of crackling noise whenever i raise or lower the gain. what kind of problem does this sound like, and would it be a cheap/easy fix?

    what years were these made? google tells me little about these amps.


    it sounds a bit louder than my ampeg b2r (which i just use as a power amp anyway) so i'd like for it to be its replacement, and to possibly serve as a slave head in future rigs. i am worried about it's potential reliability, but this still counts as probably the coolest $10 i've ever spent.
     
  2. Jun 28, 2008 #2
    JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Yamaha, Ampeg, Line 6, EMG
    Can't tell you the wattage at 4 ohms, but that sounds about right. The crackling sounds like a dirty pot, which can usually be taken care of by spraying contact cleaner into it and turning the knob briskly a few times.
     
  3. Jun 29, 2008 #3
    jjhardy

    jjhardy

    Mar 11, 2007
    spraying where, specifically?
     
  4. Jun 29, 2008 #4
    Planet Boulder

    Planet Boulder Hey, this is a private residence...man

    Nov 10, 2001
    6,482 feet above sea level
    I once had impure thoughts. Oh, and I pluck my ear hair.
    The pot won't look like this, but the basics are accurate in terms of where to spray. Basically, you'll spray where the housing meets the moving part of the pot (i.e., the external part that actually turns):

    [​IMG]
     
  5. Jun 29, 2008 #5
    jjhardy

    jjhardy

    Mar 11, 2007
    cool, thanks for the tips. also, when i turn it off it usually takes about 6 seconds to do so, and turns off with a medium volume pop. is this indicative of anything or of no real concern?
     
  6. Jun 29, 2008 #6
    jjhardy

    jjhardy

    Mar 11, 2007
    also i am now a bit unsure about the watt rating. it says "watts: 500" on the back, but looking at online photos the area below the speaker outputs say "300 watts at 2 ohms" (that area is deteriorated/illegible on my head). if this is the case, then i'm probably pushing less then 200w at 4 ohms, yet it still sounds a bit louder than my b2r power section with the randall's gain on 10.
     
  7. Jun 30, 2008 #7
    jjhardy

    jjhardy

    Mar 11, 2007
    bump. i emailed randall about the amp and it's old enough that they have no record of it.
     
  8. Jun 30, 2008 #8
    BassmanPaul

    BassmanPaul Inactive

    Aug 25, 2007
    Scarborough Ontario Canada
    No. You spray into the pot itself alongside the terminal strip.

    Paul
     
  9. Jun 30, 2008 #9
    Joebone

    Joebone Supporting Member

    Oct 31, 2005
    California Republic
    That delay between when you turn it off and when it actually pops off relates to the amp's capacitors, which you can think of as the instantaneous source of energy when you push the amp hard. Most think the more capacitor capacity the better the amp, and some think that the longer the delay between hitting the switch and true shut-off, the more capacity you have. My only caveat is whether your "pop" is the usual gentle sound, or something louder/nastier that might indicate some kind of problem.
     
  10. Jul 1, 2008 #10
    Planet Boulder

    Planet Boulder Hey, this is a private residence...man

    Nov 10, 2001
    6,482 feet above sea level
    I once had impure thoughts. Oh, and I pluck my ear hair.
    I was always told to spray where the arrow indicates in my pic and it has always worked for me.
     
  11. Jul 1, 2008 #11
    jjhardy

    jjhardy

    Mar 11, 2007

    the pop hasn't seemed much more than mild, but ive also not had a chance to play it full band volume yet. so basically you mean the higher the capacity the more headroom?
     
  12. Jul 5, 2008 #12
    jjhardy

    jjhardy

    Mar 11, 2007
  13. Jul 6, 2008 #13
    BassmanPaul

    BassmanPaul Inactive

    Aug 25, 2007
    Scarborough Ontario Canada
    Where you have indicated washes out the lubrication for the shaft. If you can't get the amp apart doing what you suggest is a way that will possibly help matters. The noise comes from the contact between the wiper and the resistive element and that is what needs to be cleaned.

    Paul
     
  14. Jul 6, 2008 #14
    BassmanPaul

    BassmanPaul Inactive

    Aug 25, 2007
    Scarborough Ontario Canada
    I think they are more akin to an effects send/return loop.

    Paul
     
  15. Oct 22, 2008 #15
    jjhardy

    jjhardy

    Mar 11, 2007
    thought i'd bump an old thread of mine to see if anyone has anything interesting to add about this amp. By now i've played with it live several times and it's worked like a charm.