Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com Reiland Pickups
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com Reilander Pickups
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com Reilander Pickups
Join TDPRI Today

Silverface Pro Reverb - reverb transformer keeps blowing...use pedal instead?

Discussion in 'Glowing Bottle Tube Amp Forum' started by GigsbyBoyUK, Jul 17, 2017.

  1. GigsbyBoyUK

    GigsbyBoyUK Friend of Leo's

    Apr 30, 2008
    Peterborough, UK
    Amp is a mid-70s 40W pull-boost master volume model.

    Second time now in about three years that the reverb transformer has blown. My amp guy suggests replacing an associated capacitor too, as that may be the culprit. I have also read that some people recommend changing the value of the cathode resistor, but I'm getting out of my depth there

    However, I mostly use a bit of slapback delay these days, rarely need the reverb, and in any case find that the reverb is the amp doesn't really sound that great to me. So I was thinking, maybe instead I'll forget about the repair and buy a reverb pedal instead.

    Just thinking out loud really. Any thoughts from you amp gurus on this?
     

  2. theprofessor

    theprofessor Tele-Afflicted

    Aug 8, 2016
    Chattanooga, TN
    There's a thread on something similar here:
    http://www.tdpri.com/threads/proble...ken-resistor-in-reverb-driver-circuit.731214/

    All this has caused me to go back and look at my SF DR schematic and compare it with the BF DR schematic on the reverb driver (V3). In particular, my SF DR shows 680 ohms for the resistor there, whereas the BF schem shows 2.2k. I've been having a bit of reverb noise as of late, and I'm certain it's not the tube. So I might just pull my chassis, too, to see how that resistor is faring in there. I've heard folks say that's one thing they do to the SF DRs (and perhaps to other models as well), citing the fact that the 680 resistor is just too small and that it runs the risk of driving the 12AT7 too hard and burning up the reverb transformer. A 680 resistor will be blue, gray, brown, I believe, with the last stripe being silver (+/- 10% tolerance). See here: http://el34world.com/charts/resistor/4BandResistor.htm?result=680+ohms++(+-+10%)

    I look forward to learning from this thread.
     

  3. robrob

    robrob Poster Extraordinaire Ad Free Member

    Dec 29, 2012
    United States
    Reverb transformers are cheap and I couldn't live with an amp with non-working reverb. It would just eat at me.

    I recommend you replace your reverb tank cables and check the wiring on the RCA jacks on the chassis. If the connection to the tank is broken, even intermittently, it is really hard on the reverb transformer. It's like running the amp with no speaker load and can cause the transformer to arc over and short out.
     

  4. Forum Sponsor Sponsored posting

  5. BobbyZ

    BobbyZ Doctor of Teleocity

    Jan 12, 2011
    Snellman MN
    Wonder if the reverb tank has been replaced with the wrong one. The impedance could be way off.
     
    AlabamaOutlaw and robrob like this.

  6. GigsbyBoyUK

    GigsbyBoyUK Friend of Leo's

    Apr 30, 2008
    Peterborough, UK
    Thanks so much for the input, people. A few things there I can check on or chat to my amp guy about. I'll report back on any progress...
     

  7. Dacious

    Dacious Friend of Leo's

    Mar 16, 2003
    Godzone
    It's definitely not normal. Could be your 12AT7 is on the way out. They are one preamp tube in that line which is buzzed hard, yes a bad cap can kill the tranny too, could be borderline shorting internally under load if it's original
     

  8. BobbyZ

    BobbyZ Doctor of Teleocity

    Jan 12, 2011
    Snellman MN
    Ment to add this the other day but got distracted.
    The input impedance on the tank is 8 ohms and the output is 2250 ohms. The reverb transformer hooks to the 8 ohm imput and that transformer is like an output transformer. (you can actually hook a speaker there, pull the phase inverter and have like a 1 watt amp)
    Anyway other tanks have input impedances much higher than Fenders like 150 ohms and much higher. Output transformers don't like huge mismatches. So I'd grab the multi meter and see what the tank reads.
    Remember you're trying to measure impedance with a meter that measures DC resistance. So like a speaker the dc ohms reading will be lower.
    I'm not saying that's the cause of the reverb transformers short life span here but it's worth checking.
     

IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.