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Old 10-14-2012, 08:51 PM   #1
ToneMasterDelux
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How difficult is it to replace a power transformer?

I have a Pignose tube amp that died and I checked all the fuses and tubes and did some research and I am almost 100% sure it is the power transformer. I know tube amps can have a multitude of problems but the transformer is only $40 and it is a part that people say should be replaced anyways in this amp.

I know how to solder and the power transformer is outside of the amp so it doesn't seem too difficult, wouldn't it just be matching the color of the wires?

I'm also wondering if it is needed to drain the caps doing this, I most certainly will anyways but I just want to know if is a bit dangerous.
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Old 10-14-2012, 09:28 PM   #2
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As long as the caps have bleeder resistors or you drain them before you work, it's pretty much matching up the colors. You'll need to trim the wires from the transformer wires to a shorter length or you get the possibility to introduce some unnecessary noise into the circuit.
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Old 10-14-2012, 09:30 PM   #3
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Its not a bit dangerous lol, the voltage kept by the caps can kill you. I used caps as granades man its serious.

But if you DO know how to drain them, have proper protection and common sense then its easy. Even if the colors dont match just follow instructions im pretty sure the new pt will say which cable is supposed to do what and just follow that in the old one if they dont match, pretty simple right?
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Old 10-14-2012, 09:46 PM   #4
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Quote:
Originally Posted by Heilz
Its not a bit dangerous lol, the voltage kept by the caps can kill you. I used caps as granades man its serious.

But if you DO know how to drain them, have proper protection and common sense then its easy. Even if the colors dont match just follow instructions im pretty sure the new pt will say which cable is supposed to do what and just follow that in the old one if they dont match, pretty simple right?


Hah, I do know how to drain them, just wanted to know I read even after draining caps they can recharge.

The issue is though that the new PT is from a Fender Bassman because the stock Piggy Tranny is shit but I think as long as the leads look the same it shouldn't be a problem.
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Old 10-14-2012, 09:48 PM   #5
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The caps can't charge if they don't have current going through them. They might pick up or hold a residual charge of a volt or 2, but that isn't even enough to shock you, let alone hurt you.
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Old 10-14-2012, 09:50 PM   #6
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Originally Posted by end_citizen
As long as the caps have bleeder resistors or you drain them before you work, it's pretty much matching up the colors. You'll need to trim the wires from the transformer wires to a shorter length or you get the possibility to introduce some unnecessary noise into the circuit.


I'm pretty sure it has a bleeder resistor (looks like there is a large cement resistor), but you are saying if it does have one I don't even need to drain the caps, (its kind of a hassle to take this thing apart)? Here is the schematic if you can tell me http://www.clarkhuckaby.com/Images3/PigMod.gif I'm new to schematics.
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Old 10-14-2012, 09:53 PM   #7
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All you're doing when you drain in the caps is placing a resistor on the leads, if the manufacturer was kind enough to do that for you all you need to do is wait after the amp is off for them to drain. Before you start working check the voltage on them. A couple volts is fine, 100 is not.
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Old 10-14-2012, 10:23 PM   #8
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Quote:
Originally Posted by ToneMasterDelux
I'm pretty sure it has a bleeder resistor (looks like there is a large cement resistor), but you are saying if it does have one I don't even need to drain the caps, (its kind of a hassle to take this thing apart)? Here is the schematic if you can tell me http://www.clarkhuckaby.com/Images3/PigMod.gif I'm new to schematics.


There are bleeder resistors in this schematic. They aren't big cement resistors, that would be a power resistor (probably screen resistors).
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Old 10-14-2012, 11:39 PM   #9
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Quote:
Originally Posted by end_citizen
As long as the caps have bleeder resistors or you drain them before you work, it's pretty much matching up the colors. You'll need to trim the wires from the transformer wires to a shorter length or you get the possibility to introduce some unnecessary noise into the circuit.



Never trust bleeder resistors to drain the caps. Always check the caps with a voltmeter, before you begin any kind of maintenance that potentially exposes you to the high voltage being stored. Caps inside of amps can store charges upwards of around 400 volts. Always practice electrical safety before assuming the manufacturer installed bleeders and that they are functioning correctly.
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Old 10-14-2012, 11:49 PM   #10
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Quote:
Originally Posted by KG6_Steven
Never trust bleeder resistors to drain the caps. Always check the caps with a voltmeter, before you begin any kind of maintenance that potentially exposes you to the high voltage being stored. Caps inside of amps can store charges upwards of around 400 volts. Always practice electrical safety before assuming the manufacturer installed bleeders and that they are functioning correctly.


Indeed. Also, the schematic the OP posted is showing a series of modifications. It does not appear the bleeders are part of the modifications, but it's always better safe than sorry.

Having accidentally taken about 500 volts by assuming a switch was functioning properly, I can assure you that you will want to check before sticking your hands in anywhere involving electricity. Even when I'm working on a pulsating DC welder that has no capacitors to store voltage, I now check for voltage (even if it isn't even plugged in).
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Old 10-15-2012, 07:23 AM   #11
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Quote:
Originally Posted by end_citizen
Indeed. Also, the schematic the OP posted is showing a series of modifications. It does not appear the bleeders are part of the modifications, but it's always better safe than sorry.

Having accidentally taken about 500 volts by assuming a switch was functioning properly, I can assure you that you will want to check before sticking your hands in anywhere involving electricity. Even when I'm working on a pulsating DC welder that has no capacitors to store voltage, I now check for voltage (even if it isn't even plugged in).


500??? God try 800 from three different phases... It is NOT fun man.

Just drain them, it wont take that long to do that. Then when replacing. It may be a different PT but as long as it's in specs with the old one you should be fine.
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