60 Cycle Reverb Hum on Rivera R55-12 Amplifier

[tbonesullivan]

Either I haven't noticed this before with other amps, or it's something specific to this amp. Anyway, I was getting a lot of hum on the reverb for the amp. So, I finally got around to cleaning all the tube sockets, all the input outputs, the reverb RCA jacks, etc. I tried swapping out the reverb driver tube.  The hum was still there.

I disconnected the reverb cable from the chassis: silence.  Then i tried just the cable, not attached to the tank, and there was more hum the closer I got to the tank. Mind you this was with the reverb at around 6, which is LOUD on this amp. I've never had to really crank the reverb.  So I plugged it back in, picked up the amp (it's not that heavy) and slowly rotated it, and as expected, the volume of the hum changes, just like with a single coil guitar.

So, is this a bad thing, or just a thing? Is the tank going bad? Should I try grounding the tank? Replacing it? I'm starting to see why some brands encapsulate their reverb tanks in vinyl bags.

EDIT: I just tried swapping out the RCA cable.. no change. Also, I have all my gear running through a Carvin AC120 Power Conditioner. Voltage and Safety ground lights are lit.

[Bloozguy]

3 hours ago, tbonesullivan said:

Either I haven't noticed this before with other amps, or it's something specific to this amp. Anyway, I was getting a lot of hum on the reverb for the amp. So, I finally got around to cleaning all the tube sockets, all the input outputs, the reverb RCA jacks, etc. I tried swapping out the reverb driver tube.  The hum was still there.

I disconnected the reverb cable from the chassis: silence.  Then i tried just the cable, not attached to the tank, and there was more hum the closer I got to the tank. Mind you this was with the reverb at around 6, which is LOUD on this amp. I've never had to really crank the reverb.  So I plugged it back in, picked up the amp (it's not that heavy) and slowly rotated it, and as expected, the volume of the hum changes, just like with a single coil guitar.

So, is this a bad thing, or just a thing? Is the tank going bad? Should I try grounding the tank? Replacing it? I'm starting to see why some brands encapsulate their reverb tanks in vinyl bags.

EDIT: I just tried swapping out the RCA cable.. no change. Also, I have all my gear running through a Carvin AC120 Power Conditioner. Voltage and Safety ground lights are lit.

The vinyl bags help prevent acoustic vibrations from reaching the reverb tank, but they do nothing to prevent electrical interference like the kind that will cause hum.

gtrdaddy is right...move the amp around the area to see if the him decreases. The tank springs are probably acting like an antenna to pick up that hum.

[tbonesullivan]

I moved it around the area and the house, and found some orientations where it definitely has less/no hum. It's just something I've never noticed with other amplifiers I have owned. Maybe the reverb circuit is more sensitive than most?

[texwest]

You might try unscrewing the tank and moving it around inside the cabinet. and see if it helps.  The tanks proximity to the speaker can sometimes be a problem.

 

[tbonesullivan]

I tried moving the tank outside the cabinet entirely. Still does it, based entirely on the orientation of the tank.  Just never experienced this kind of hum from reverb before. It is a very loud reverb system though, especially compared to the ones on my other amps.

I actually emailed rivera, and they suggested swapping out the tank, so I think I am going to try that. Before that, I also will probably try to hook it up to another amplifiers reverb tank to see if I still get the same hum.

[JohnnyB]

Perhaps you could try swapping in a compatible reverb driver tube with less gain. Also, how old is your house? Does any of the house wiring precede up-to-date code?

[tbonesullivan]

I've tried several different reverb driver tubes, same issue.  I'm just using another tank to see if I get the 60 cycle hum from it.

This is the tank Rivera suggested: https://www.tubesandmore.com/search/node/8bb3c1b?cats[0]=260

[tbonesullivan]

I just ordered the new Tank for the amp. Should get here in a week or two. Hopefully that fixes the problem. If not, the amp probably hasn't been serviced in 25 years, so I'll take it down and have them take a look at it.

Now if only the reverb tank in my carvin Vintage 16 would stop having connector oxidation. Sadly I can't replace it because no one in this country has the right tank available. It's got a "G" rating for Input / DC Resistance: 8333 / 735 Ohm. That's so high that most of the accutronics charts don't even go up there.

[tbonesullivan]

Got the new tank in along with some T-shirts from antique electronic supply. So, first I replaced ALL the tubes with known good tubes.

Problem was still there.

Replaced the reverb tank. Amp still has reverb, and there's still 60 hz hum whenever the reverb is up above 2. I then tried out my Marshall TSL122, Mesa DC-5, and Carvin Vintage 16. None had reverb related 60Hz hum, even with the reverb dimed. The noise floor on the amp in general also seems to be rather high, but when I plug in a connector to the effects loop in, it goes close to silent.

This is definitely sounding like it's time to take it to Dave's sound repair.

[crunchee]

What tubes are in there for the reverb driver and reverb recovery?  Are you using a lower-rated tube like a 12AT7, or a higher rated tube like a 12AX7?

[tbonesullivan]

The amp is designed for 12AX7 tubes in all positions, confirmed by the manual and schematics. It still had the original Rivera branded tubes in it when I got it. I also replaced every single tube, preamp and power, and the problems still remain. It's also a lot noisier than other amps I have that are the same age or older. The effects loop is op amp driven, with an output and input control.

I did talk to rivera CS again, and they said it sounds like it wasn't used much, so it could have had some caps go. Either way, the repair guy will figure it out.

[Thundersteel]

14 hours ago, tbonesullivan said:

so it could have had some caps go

If they're filter caps, those would be the culprit.