FDP Forum / Loud Humming Noise / 3 messages in thread.

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WEBZIGHT



USA

If It Ain't Broke, Don't Fix It!
Feb 10th, 2017 01:50 PM        

Greetings All,<br /> <br /> I have a Fender Hot Rod Deluxe that I purchased new back in 1996 or 97 that presents a very loud humming noise after coming off STANDBY!<br /> I have replaced ALL the tubes with matched set (finals) new ones and the same thing occurs! (Thought it might be a microphonic tube)<br /> I suspect the power supply filter caps are the issue as I've seen this before in other consumer tube equipment I worked on back in the day when everything was tubes (telling my age);-)<br /> I have checked the Signal Caps and they do not appear shorted! <br /> My next step is disassemble the chassis circuit board and look at the power supply filter caps!<br /> If anyone has had this issue and fixed same please pass on any helpful advice!<br /> I started my electronics career working on tube type TeeVees, Radios, and Stereo/Audio Equipment! ;-)



Hammond101

Contributing Member
**********

So. Cal. USA

Feb 10th, 2017 02:08 PM        

20 year old filter caps certainly could be the cause and since you are capable of doing the work they should be changed just because of age.<br /> <br /> The other thing to check is the shorting jacks most likely on the FX loop. Connect a guitar cable between the in and out jack and see what happens. Input jacks on these also fail as do their solder pins to the pads on the main board.<br /> <br /> I'd recommend an ESR meter for testing the caps in circuit. At least you know what your in for before pulling the board loose. Best $100 you'd ever spend on test gear short of a DVOM. Search ebay for "Blue ESR Meter".<br /> <br /> I've also see the solder joints on the power tube sockets fail, hum, noise, ugly sounds. I always re-float these with a HRD on the bench.



WEBZIGHT



USA

If It Ain't Broke, Don't Fix It!
Feb 10th, 2017 10:42 PM        

Thanks Hammond 101 for the feedback ;-)<br /> <br /> Don't have an FX loop but I did a physical inspection and found cold solder joints on the two 5W resistors and associated diode (+/-16 VDC)<br /> <br /> The first 200 µf filter cap was puking it's guts so I have ordered a whole new high performance set and will replace them ALL including the bypass caps ;-)<br /> <br /> Remarkably the the tube solder joints all still look new ;-) (Inspected with 10X glass)<br /> <br /> Fingers crossed that the caps are all there is to this problem ;-)



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