Hummmmmmmm........

Joe M

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I have a Fender 64 handwired DRRI, probably the best amp I've ever had or heard. I'm probably nit-picking here, but I noticed the other day that there's a slight hum when the amp is at idle. Definitely not noticeable when I'm playing. I usually have just a bit of reverb on, just to thicken things up a bit. Messing around, I found that the hum goes away when I turn the reverb off, either with the fs or the knob. Gets louder the more I turn the reverb up. Even when dimmed, and deep in surf city, the hum isn't noticeable when playing. So, what do ya think, forget about it and just play guitar, or some (easy) fix I could try to get rid of the hum?
 

Sea Devil

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Depending on the source of the hum, it might or might not be easy to fix.

Easy: turn the reverb pan 180 degrees; it may be coming from the transducers in the pan being too close to a transformer. Move the reverb cables around. Disconnect the foot switch if it's connected; connect it if it's disconnected. Maybe, just maybe, try different tubes; this will certainly change many characteristics, but not necessarily the hum. Try a 5751 (a real one, not current production pseudo-5751s) in the reverb return instead of the 12AX7/7025.

Hard: Test and measure all the components in the signal path and replace any that are far out of spec, especially carbon comp resistors and ceramic disc caps and electrolytic coupling caps.

I have the same amp, and I did (or at least tried) all of these things. I got rid of it (the hum, not the amp!) eventually.
 
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Sea Devil

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I have to add that in most amps, you'd also want to check the grounds, but that would only apply to your amp if they've been altered. Likewise with lead dress.

An untouched DR from that era should be very solid in both of those areas.

I feel much the same way about my '64. It's world-class.
 

Joe M

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Sea Devil, thanks for the tips, I’ll give them a try. FWIW, you may have missed that my amp is a reissue, not a vintage ‘64. :)
 

Sea Devil

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I certainly did! Almost everything I said that has to do with the deterioration of parts over time is meaningless in that case. But do check the coupling caps.
 

Joe M

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I certainly did! Almost everything I said that has to do with the deterioration of parts over time is meaningless in that case. But do check the coupling caps.
The only thing I'm gonna check are the V3 and V4 tubes, that Wally confirmed, might be the problem. If swapping them out doesn't help, I can live with the hum, it's really not that big a deal.
 

Sea Devil

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Of course Wally's correct. I absolutely should not have put that option in the "maybe" category.

I think I was working from my own definition of hum, when of course we all use words differently. Either that or I was just being stupid. The fact of the matter is that whenever there's any issue at all in the reverb circuit, those tubes should be the first suspects.
 
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Wally

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Well, now don’t take my suggestion as the only possibility. I tend to eliminate the simple things first. Hums can have various sourc3s….tubes, tone caps, coupling caps, electrolytics, power tube imbalance, grounding problems.
 

Sea Devil

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Not power tube imbalance or the PI in this case. It's only in the reverb cicrcuit.

And it's still only a "maybe." I just over-emphasized its "maybe-ness." And hey, it's still pretty easy to rotate the reverb pan and see if that's the problem. It might even be a pan that's naturally noisy, just as some tubes are.
 
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Joe M

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Update: swapped both V3 and V4 tubes (one at a time) with little, if any change. So, as I said, it’s such a slight hum, I can easily live with it. Might still try the tank rotation.

Thanks, Sea Devil and Wally.
 

King Fan

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Smart guys, is a little reverb hum 'normal' here?

@Joe M , to clarify, you’re saying this is a handwired reissue, not a vintage '64? Is it the Fender one or one of the George A. or other versions? How old is it?
 

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Smart guys, is a little reverb hum 'normal' here?

@Joe M , to clarify, you’re saying this is a handwired reissue, not a vintage '64? Is it the Fender one or one of the George A. or other versions? How old is it?

good question. There are no handwired DRRI. The handwired version of the DR that Fender produced is called the ‘64 Custom Deluxe Reverb.
 

Sea Devil

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That's the "lead dress" I was talking about. Sometimes going inside the amp and moving the loose wires around makes a difference. Ground wires, usually white-ish or yellow cloth, sometimes like to be grouped together and placed as close to the metal chassis as possible. Sometimes apparently random, weird positioning of the wires works better.

I know everyone warns about the dangers of working inside an amp, and rightly so, but if you only touch the innards with something non-conductive like a chopstick or plastic tweezers -- never with your bare hands or anything with metal parts -- you can safely move those wires around even when the amp is live.

Now, before you kill yourself, one more caveat: if you accidentally drop your non-conductive object onto/into the chassis, you need to use something equally non-conductive to get it out!

That's the upper limit of what someone with zero experience working inside an amp should do, IMO.
 
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Joe M

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That's the "lead dress" I was talking about. Sometimes going inside the amp and moving the loose wires around makes a difference. Ground wires, usually white-ish or yellow cloth, sometimes like to be grouped together and placed as close to the metal chassis as possible. Sometimes apparently random, weird positioning of the wires works better.

I know everyone warns about the dangers of working inside an amp, and rightly so, but if you only touch the innards with something non-conductive like a chopstick or plastic tweezers -- never with your bare hands or anything with metal parts -- you can safely move those wires around even when the amp is live.

Now, before you kill yourself, one more caveat: if you accidentally drop your non-conductive object onto/into the chassis, you need to use something equally non-conductive to get it out!

That's the upper limit of what someone with zero experience working inside an amp should do, IMO.
Nope, that ain’t gonna happen, no way, no how. As I said, the hum is so small,
 




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