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FDP Forum / Amp Mods, Repairs, and Projects / fender HRD 3, loud buzzing when taken off standby

bean 14

Australia

Jul 8th, 2019 12:08 AM   Edit   Profile  

hey guys, I'm having an issue with my HRD where whenever I turn off the standby switch the amp buzzes loudly, the buzz isn't effected by the volume or reverb pots and goes away when I turn standby on, it isn't guitar lead related either as it does it without anything plugged in.

here is a sound sample: https://www.dropbox.com/s/edghbnu2a4e9jvf/IMG_1890.MOV?dl=0

thanks in advance for any help

https://www.dropbox.com/s/edghbnu2a4e9jvf/IMG_1890.MOV?dl=0

Peegoo
Contributing Member
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If irritation occurs

discontinue use.
Jul 8th, 2019 08:14 AM   Edit   Profile  

Because the hum is unaffected by the volume control, the source of the noise is not in the preamp section.

It's probably in the power section or power supply. It may be as simple as a poor ground connection.

Gently pull the power tubes and replace them. This cleans the contacts and establishes a better electrical connection. Test the amp to see if the problem still exists.

If the hum is still there, it might be a bad power tube. It could also be one of the filter caps in the power supply has quit the job.

The best way to diagnose these noise issues is to trace the source of the noise with a scope. If you don't know what you're doing, *do not* go poking around in the chassis because even when unplugged, an amp can deliver a lethal zap,

I am not an expert in this stuff; just passing along what I've encountered in the past.

Peegoo
Contributing Member
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If irritation occurs

discontinue use.
Jul 8th, 2019 08:15 AM   Edit   Profile  

Welcome to the FDP!

willie

Too Near Atlanta GA

Amp Tech Emeritus
Jul 9th, 2019 03:59 PM   Edit   Profile  

Could be caused be several things actually, but it sounds a lot like an output tube bias issue...that is, your output tubes are running too hot due to insufficient bias voltage. Usually though, if they are humming like that, you'll also see your output tubes "cherrying up" a bit. Could also be due to a bad power supply filter cap or solder joint on one of the filter caps. There are certainly other likely causes but those two are most common based on the conditions you stated.

w

pdf64

UK

Jul 9th, 2019 04:13 PM   Edit   Profile  

So the amp is sounding ok apart from the buzz?

Try your 'known good' matched pair of power tubes in there and review.

bean 14

Australia

Jul 9th, 2019 04:53 PM   Edit   Profile  

thanks for your help guys, i pulled the back of the amp off and couldn't see any obvious lose connections or band joints so i then pulled one of the power tubes out and it had this green corrosion stuff on it could this be contributing to the issue?

pdf64 the buzz distorts the guitar sound so you can't really play over it

Peegoo
Contributing Member
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If irritation occurs

discontinue use.
Jul 9th, 2019 07:06 PM   Edit   Profile  

Yes, that could be the issue because corrosion or burned contacts on the tube pins can reduce or prevent the clean transfer of electrons.

willie

Too Near Atlanta GA

Amp Tech Emeritus
Jul 9th, 2019 07:46 PM   Edit   Profile  

Indeed...

w

bean 14

Australia

Jul 10th, 2019 12:15 AM   Edit   Profile  

hey guys the issue is fixed!!! it ended up being a dirty power tube socket thanks for all your suggestions

willie

Too Near Atlanta GA

Amp Tech Emeritus
Jul 10th, 2019 06:28 AM   Edit   Profile  

Well, there ya go.... :)

w

Peegoo
Contributing Member
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If irritation occurs

discontinue use.
Jul 10th, 2019 05:30 PM   Edit   Profile  

Probably as willie described: the power tube lost bias due to a poor/dirty connection in the socket.

Know what makes a great little scrubber for power tube sockets? A length of wound E string.

Drill a little hole in the end of a 1/4" diameter dowel 2" long, and CA glue a 2" length of old E string in there.

Dunk the string in some solvent and scrub each socket hole using the tool like a pipe cleaner.

IMPORTANT: Remember to unplug the amp and discharge the filter caps before doing this because you can get a severe jolt poking around in a tube's socket.

pdf64

UK

Jul 11th, 2019 02:08 AM   Edit   Profile  

Good tip Peegoo, I love homemade tools :-)

bean 14, how did you clean the green deposits away?
Any idea where it might have come from?

Peegoo
Contributing Member
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**********
**********
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If irritation occurs

discontinue use.
Jul 11th, 2019 08:26 AM   Edit   Profile  

pdf64, you can use an old bass string for larger octal pin sockets.

Make a double-ended tool; one with the small guitar E string on one end for 9-pin sockets and on the other end have the fatter bass string for octals.

Cheers, mate!

FDP Forum / Amp Mods, Repairs, and Projects / fender HRD 3, loud buzzing when taken off standby




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