FDP Forum / 5E3 volume fluctuations/ 7 messages in thread.

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Modal Magic

Contributing Member
********

MBJ, Highway Hound.

You Can't Bend It Aussie!
Apr 20th, 2017 02:31 AM        

What are probable causes of 5E3 volume fluctuations as in randomly decreasing and increasing to normal level?<br /> <br /> Associated with this are noises that sound very much the same as static produced with an unshielded pick guard. <br /> <br /> It's not the guitar that's causing the problem because I'm using a shielded Strat that definitely doesn't make the sound when I rub the pickguard (and I've also used a variety of guitars including Ibanez and Gibson).<br /> <br /> Things I've done:<br /> - Checked as much as possible for bad solder joints.<br /> - cleaned tube sockets.<br /> - replaced all tubes including the rectifier.<br /> - checked for security of mechanical terminations.<br /> - checked filter caps for leaking.<br /> <br /> It would be awesome if definitive causes are provided. Such things as bad solder joints in specific parts of the circuit, specific resistors and capacitors, for example. surely there would be experience out there that narrowed such a problem down to component level?<br /> <br /> Everything on the internet is very generic so specifics from first-hand experience would be great. Any help will be appreciated.



pdf64



UK

Apr 20th, 2017 05:03 AM        

Is this a real 50s Fender 5E3?<br /> If not please provide details.<br /> Whichever, does it have any mods or deviations from the 5E3 schematic / layout / parts, see link?<br /> <br /> Does the static noise require an input signal for it to manifest, or does it ever occur when the amp is idling?<br /> <br /> Without more info and testing (which will require requisite competence and resource) I suspect that your hopes for an exact diagnosis over the internet may not be realistic.<br /> <br /> A voltage survey of the amp would be a good starting point.



guitarcapo



U.S.A.

Apr 20th, 2017 10:26 AM        

I agree about checking voltages everywhere.<br /> <br /> Check along the rail (the resistors associated with the filter caps)<br /> <br /> Check plate voltages at each tube.<br /> <br /> Check all plate resistors and dropping resistors across the filter caps to make sure none are partially burned to higher values. One of these might be burning "open" reducing voltage to one of the tube plates.<br /> <br /> There could be other reasons...but I usually suspect a resistor burning out...and one under high voltage would be more likely.



Modal Magic

Contributing Member
********

MBJ, Highway Hound.

You Can't Bend It Aussie!
Apr 21st, 2017 04:38 AM        

It's a 2008 '57 Deluxe RI with no modifications.<br /> <br /> The static noise occurs randomly when I pick guitar strings. There is no correlation between how hard or where the picking occurs. When the volume reduces it sometimes occurs at the same time as the static occurs, some times not. The static occurs whether the volume is up or down.<br /> <br /> I don't know if this will help but the amp loses it's chimey goodness when the volume reduces sounding flat and loosing touch dynamics.<br /> <br /> To clarify, I'm after real life component failures that are known to have caused similar issues in other amps, not an exact diagnosis. It will help me focus on parts of the circuit that could be causing the problem.<br /> <br /> Thanks guitarcapo, I'll do a thorough physical inspection of the resistors you mention. It sounds like a good starting point.<br /> <br /> Edit- I assume all voltages are checked with one prong to ground?



pdf64



UK

Apr 24th, 2017 02:24 AM        

See the link for Tweed Deluxe schematic with example voltages.<br /> Yes, unless otherwise noted, voltages are normally with respect to circuit 0V; in this case, as normal with vintage Fenders, the chassis looks to be used as the 0V bus.<br />



ECS-3

Contributing Member
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USA / Virginia

Apr 24th, 2017 09:09 AM        

The first thing I would do, before changing anything, would be a voltage survey. Especially the plate voltages on every tube. There are a lot of issues that will manifest themselves as a voltage problem somewhere in the circuit.



guitarcapo



U.S.A.

Apr 24th, 2017 11:59 AM        

Set your meter to voltage DC and volts not mV. Touch one end to the chassis (ground) and one end to the pin corresponding to the voltage you are checking. (power tube plates, preamp tube plates, voltages along the rail) Don't worry about negative or positive if you are a hack like me....I just want to know the amount.<br /> <br /> If you read a plate voltage that is WAY lower than the schematic states, you might have a plate resistor that burned up and drifted too high. You can check the resistor value by setting your meter on ohms resistance and measure across the suspect resistor.<br /> <br /> If the plate voltage is too HIGH, the resistor might have burned towards less resistance...again replace the resistor if it reads too low.<br /> <br /> You can also check voltages at the cathodes of all tubes as well and check the spec of cathode resistors everywhere.<br /> <br /> Be aware that these are high voltages...especially at the rail and you need to be VERY careful taking voltages at the "rail" to avoid shocking yourself.<br /> <br /> Bias isn't an issue with these amps because they are cathode biased...but you might want to also check the cathode capacitors at the power tube and preamp tubes.<br /> <br /> I can think of other issues like a cold solder somewhere, bad tube, or something being intermittently grounded in the signal chain. I usually use a wooden chopstick approach for that sort of stuff....Which I would explain more once all the voltages and tubes are checked.



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