Silvertone 1484 Rehab Questions

Discussion in 'Amp Tech Center' started by Huddy, Nov 30, 2019.

  1. Huddy

    Huddy Tele-Holic

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    So I've had this 1484 for the better part of a year and a half sitting because I wanted to work on it myself and at the same time wanted to know what exactly I was doing and not die. I feel confident that that will not happen because I'm not 100% confident in my knowledge which keeps me on my toes and extra cautious. Here's what I've done so far and and the result.

    When I bought it it had very little output at all but it did play so after 5 mins a research voltage doubling electrolytic capacitors.

    I replaced voltage doubling capacitors at my output tube plate voltages and my B+ are a smidge high which is accounted for by the higher wall voltage - but they're in the ball park - 505+/- as opposed to 480.

    Here's my voltages compared to what the schematic says the should be in parentheses.

    Screen grids are 380v (340v)
    Negative Bias is -35v (-36v)

    To me those are all within the realm... When I get to preamp and and reverb tremolo tubes is where things get whacko.

    V1 Plates are 324 (100v)
    V2 Plates are 333 (93v)

    V3-1 376v (225v) (Phase inverter)
    V3-6 280v (100v) (Phase inverter)

    V4, V5, and V6 are also out of whack (reverb and tremolo)

    So my question is, could this be an issue with choke? The filter capacitors within the can cap? The resistors between the sections or the can cap?

    If I were to replace the can capacitor what would acceptable values be? I can get a 3 separate caps but it's so tight I really don't want to. I'm kind of dreading it.

    Thanks for the help in advance!
     

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  2. Huddy

    Huddy Tele-Holic

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    I also replaced the power cable to 3 prong and bypassed the death cap and ground switch - shouldn't be a factor. Cathode bypass caps were also replaced. The resistors are all original carbon comp but have been measured to be within 10% ish.
     
  3. Bendyha

    Bendyha Friend of Leo's Silver Supporter

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    The screen grid supply is comming of the back of the choke, and as you say, the voltages are not to off whack there, but stangly the PI supply comes off the same node, yet it is way hogher than it should be:confused:.
    If the cap can is still the original, then I would certainly want to replace it anyway, and those two 68K resistors have likely drifted...what do they measure?
    20µ 10µ 5µ at 450V is the original can, might be hard to find one the same, but that isn't really a big deal, this capacitor-450v-20 20 20 should be fine, but you might want to add an extra 6,8µ cap in series with the last one (that will lower its combined capacitance to 5µ) to keep the bass limited a bit.
    This may fix the problem, but I would do it first anyway. The fact that the voltage is not pulling down is a sign that either the resistances are to small to drop the voltage enough, or the current draw is lower than expected.- are all the tubes in and working, is the tremolo working ?
     
  4. Huddy

    Huddy Tele-Holic

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    The 68 kΩ Resistors meter around 80 kΩ.

    Currently plugged into current limiter with no tubes just to make sure I won't explode - I'm a semi-noob and know just enough to be terrified of dying.

    Install tubes with variac slowly dial up and cross fingers?
     
  5. D'tar

    D'tar Friend of Leo's

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    Stay on the limiter with tubes in untill you are confident the circuit is healthy. If all is well you will then see voltage dropping as the circuit has a load on it (tubes)
     
  6. jsnwhite619

    jsnwhite619 Friend of Leo's

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    I just fixed a 1482 for a friend who got it free. Tubes were busted, but the voltages were sky high. The whole amp was in amazing condition I side and out. As far as I know it may have left the factory this way, but the first or second dropping resistor in the filter section was scorched looking. Turns out the 22k dropping resistor on the schematic had a scorched 20 ohm resistor in its place. Swapped it out & new tubes and everything was golden across the board.

    Funny thing is it had a cap job already. I wonder if someone did that trying to fix it, it didn't work, so they just quit.

    Anyway, check the value of the dropping resistors on the power section if the voltages are way too high.

    Sent from my moto g(6) using Tapatalk
     
  7. Huddy

    Huddy Tele-Holic

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    All plate voltages are stable with tubes installed. I don't know what I don't know. Channel one has some crazy constant bass hum once your turn the volume up. Channel 2 has no significant hum. There is a bunch of random AM Radio sounding static on both channels. I'll play around with the tube positions and see if anything changes anything.
     
  8. Huddy

    Huddy Tele-Holic

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    Ay O! AM Radio sounding static is gone after some pot cleaning. Still got that bass hum in channel one. Will clean tube sockets and pins and cross my fingers. reverb works and sounds meh. Tremolo is great at the right setting
     
  9. Huddy

    Huddy Tele-Holic

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    Cleaned tube sockets and pins. All unwanted noises are gone. I then swapped out the original input jacks to a fender-esque hi-lo shorting style. It's pretty killer. I'm kinda waiting on the can cap to crap out but until then she's rockin'
     
    jsnwhite619 and Bendyha like this.
  10. zook

    zook Friend of Leo's

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    This is relatively normal for this amp.
     
  11. Bark

    Bark NEW MEMBER!

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    I believe that Weber (the speaker and amp kit company) has that 3 section cap you want. 20-10-5 uf 450 volt. I just disconnected mine and put separate cans on the inside. Leave the old one attached for looks . I didn’t have a 5 UF so I put 2 10 Uf caps in series to get 5.
     
  12. Dacious

    Dacious Poster Extraordinaire

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    Err, don't wait for it to crap out. It probably won't die, just contribute to worse sound but if it does, you could lose your vintage output transformer. After 50 years they'll be dried up inside.

    Even if it 'sounds Ok' change it sooner rather than later. These amps weren't imbued with overly large filters. They can't afford to lose any. I would stick to within 10% of spec - the old PT might not like too much charge cycle strain.
     
  13. Huddy

    Huddy Tele-Holic

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    I'm probably wrong but the can cap shouldn't affect the output transformer should it? The can cap is on the other side of the choke. The voltage doubling caps going to the output transformer center tap have all been changed with quality F&T caps of the original values. I'm no genius - I do not know what I don't know, unfortunately.
     
  14. Huddy

    Huddy Tele-Holic

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    I just looked on weber and couldn't find the multi-section version but I did find a ham radio company called Hayseed that reproduces old style can capacitors on a custom level. When I get back from vacay I'll measure it and get them the dimensions... hopefully it's easy for them to make and me to order. (crosses fingers)
     
  15. Dacious

    Dacious Poster Extraordinaire

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    If a cap goes out anywhere in the amp and it's between a power rail and ground and creates a dead short it potentially will pull too much current. The choke is just a smoothing inductor and minor voltage dropper, it in itself won't affect current draw either way.

    The caps in this amp serve the same function. They smooth the rectified DC voltage from _ _ _ _ _ to ------------------ so that you don't get buzz.

    But when if they short internally they can indeed cook stuff. Maybe the choke if lucky. Maybe your PT.
     
  16. jsnwhite619

    jsnwhite619 Friend of Leo's

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    The 1482 & 1483 used smaller cans than are available - or that are easily available - and I snipped the leads, left it in there for looks, and replaced with regular filter caps. I think that's the common practice for recapping Silvertones these days.

    Sent from my moto g(6) using Tapatalk
     
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