=-( low hum that sounds about 50Hz

[YellowJacket]

Hello all,
after four months away from my Dual, I plugged it in and tried it with my thiele 2 x 12. I absolutely love the cab and I can dial in a great sound with the gain channel on vintage. The clean is also absolutely amazing. Well, I was playing away for about 10 minutes, annoying the new neighbors, and when I switched onto clean I noticed a low, bassy, subwoofer-ish hum around a piano A0. (55Hz) I played an open A chord and I noted that the hum is slightly out of tune which means it is most likely a 50Hz tone. The hum only shows up when I've been playing awhile and it only is on the clean channel. I was worried I was having transformer problems but maybe I should swap my preamp tubes around? Do you have any suggestions for troubleshooting? This is disappointing for me, especially when I finally have a tone I absolutely love!! Here is to hoping there isn't some circuitry that is frying on me!

 

[fluff191]

You have a preamp tube that is going the way of the buffalo.

 

[YellowJacket]

Thank goodness. Now I just need to find a tube vendor here on the Canadian west coast! I was about to start swapping preamp tubes but I was just checking to make sure that it wasn't a huge problem. Hey, since it only shows up on the clean channel, does this mean it is V2? Last time I had a problem specific to that channel I narrowed it down to that tube slot and it is the most recent tube I replaced =-( I guess I'll just have to buy a 12ax7 and start playing the trading game!

 

[YellowJacket]

Boo Bad NEWS!!!

I have been swapping tubes all day in between cleaning up the new place and that sub rumble was remaining. It would get louder when I turned up the bass pot and it was only present on the clean channel. I checked on the site here and apparently V3 is attached to the bass pot so I swapped that along with other tubes but to no avail. I reduced the noise and hum slightly, the most when switching V2, but that low sub rumble wouldn't disappear. In the end, I swapped EL84s for my backup pair which I know still work, but the problem persisted. Then I swapped out the EL-84s and yellow jackets for 6L6s and the sub rumble ceased. So far the only tubes I have not changed are a rectifier tube and V4, which is apparently for the effects loop which I never use. (I haven't ran my amp at 100watts for ages so it consistently working with one rectifier tube and two power tubes)
I then started reading some information on the yellow jackets and I heard stories of marshall people who were cooking them left, right, and center. I read a lot of technical mumbo jumbo about how the design for these converters is flawed. I'm wondering who else has had experience with them. Aside from this one issue, they have served me well in volume sensitive situations for many years now. I'm wondering if mine are finally about to cook and if I need new ones or I should simply get a volume attenuator instead.

 

[Anonymous]

Maybe try new EL-84s. I actually had the same problem as you with an old set of 6L6s. Swapped them out and the problem went away instantly.

I'm not surprised to hear Marshall owners frying the Yellow Jackets. Marshalls typically are run very hot, so it would make sense. However, Mesas - and Rectos in particular - are run very cold for less power tube saturation. Again, try switching out the EL-84s. I'll bet that fixes it!

 

[mikey383]

Have you tried moving the amp to a different location? It sounds like you're picking up interference somewhere.

 

[Anonymous]

Have you tried moving the amp to a different location? It sounds like you're picking up interference somewhere.

Probably not the case if he experiences the issue with the clean channel and not the dirty. Also, interference most likely won't be solved by swapping out tubes.

 

[mikey383]

Could say the same thing about a tube issue

 

[YellowJacket]

Well, I am no farther ahead here. I swapped back in the yellow jackets and flipped the Variac switch from 'bold' to 'spongy'. The sub frequency hum was gone all morning but then I discovered I had an impedance mismatch (stupid custom configurations) so I rewired my speaker leads just now. I haven't tried it but here is to hoping the noise is gone. I have to track down a tube vendor on the West Coast rather than shopping at box stores but ya, I think I'll replace the el 84s and eventually probably all my preamp tubes. I haven't retubed the amp properly in about five years so I am wondering if it is a problem.

Man, tube amps are so finicky and the trial and error process makes absolutely no sense.

Off topic, I am bothered by my gain tone at the moment. There are these spikey high frequencies that seem to jump out. I'm really wondering if it is the room but it is hard to tell. My cello also sounds slightly brittle in here as well.

 

[Anonymous]

Probably the room. I had that issue a few times. It's really annoying when the highs jump out like that, but it happens.

 

[YellowJacket]

The Sub hum is gone for now. I played my gear with the correct impedance match and it was sounding great, but I continue to be perplexed with the 'solution'. I really didn't do anything aside from swap two preamp tubes (which only lessened the problem) and switching the variac from 'Bold' to 'Spongy'. I guess the problem is 'in remission'.

I'm glad since I absolutely love the Yellow Jackets. The clean channel becomes so bluesy with such a nice sparkle when you dig into the strings and the gain tone is still fat and beefy, albeit at lower volumes. The neck pickup on my Les Paul absolutely LOVES the clean and the bridge pickup is very clear with the gain channel on the head, such a great match.

Ya, I recall we had a basement back in Winterpeg where every piece of gear sounded absolutely terrible in there so I'm quick to suspect the room when the gear sounds fine elsewhere. I can't wait to gig with this rig but I guess I'll have to make some musician friends to make this desire a reality! I have to say, the Thiele 2 x 12 is such a huge upgrade over the Peavey 1 x 12, even though the Peavey also has a Celestion in it. I ABed them and the Peavey sounds thin, trebly, and brittle by comparison. Good times!

 

[YellowJacket]

Majic Eight: RE your advice to get new EL-84s

Ok, I went down to the local music store and got a duet of new EL-84s. They were shipped by Peavey but still badged as a couple of JJs. The guitar guy at the store told me that the Peavey shipped JJs were the lowest price I would find for tubes anywhere which was true, at under $20 for the pair Canadian.

Well, I plugged them in and immediately noticed that they are louder and tighter. I played on the clean for awhile but when I hit the gain channel, the amp sounded like a different beast entirely. The tone was an aggressive snarl with very defined highs, a tight thumpy bass, and a hot midrange bark which was incredible. The distortion tone before was thin and lifeless with a terrible treble spike but ya, my little ministack is roaring now! I'd say these EL-84s really sound like the little brother to EL-34s. With a vox-ish warm clean and a huge thick distortion tone, I am one happy camper.

 

[Anonymous]

Majic Eight: RE your advice to get new EL-84s

Ok, I went down to the local music store and got a duet of new EL-84s. They were shipped by Peavey but still badged as a couple of JJs. The guitar guy at the store told me that the Peavey shipped JJs were the lowest price I would find for tubes anywhere which was true, at under $20 for the pair Canadian.

Well, I plugged them in and immediately noticed that they are louder and tighter. I played on the clean for awhile but when I hit the gain channel, the amp sounded like a different beast entirely. The tone was an aggressive snarl with very defined highs, a tight thumpy bass, and a hot midrange bark which was incredible. The distortion tone before was thin and lifeless with a terrible treble spike but ya, my little ministack is roaring now! I'd say these EL-84s really sound like the little brother to EL-34s. With a vox-ish warm clean and a huge thick distortion tone, I am one happy camper.

Awesome! Glad the new tubes are working well.

Again, I had the same issue with older 6L6 tubes. When I went into spongy mode, the hum was gone, but with diodes or on bold there it was. I'm going to take a guess and say it's just because with spongy, there's less power going into the amp and so it's easier to manage the current.