Blues junior hum - what is normal and what isnt?

[xjimmyleungx]

I bought a used MIM Blues Junior (from a craigslist equivalent site) today. I noticed a significant hum even at bed room volume. This is my first tube amp, but I'm aware that tube amp does have some hum.

The hum has these characteristics:
- NOT related to the reverb amount
- worse after pressing the fat switch
- the hum is constant. NO popping or rattling type of sound
- starts to be audible at master=3 volume=3
- hum is significant at master=6volume=3, or master=3volume=6

Is this normal?

If I'm in a studio or jamming with a band, this would probably be nothing. But I intend to use it at home, and with this kind of hum even at bed room level...that seems like a bummer.

I'm wondering if I should return this to the seller or bring it to a tech.My apologies if this is normal or if I'm over-reacting!!

 

[Billm]

Blues Juniors are fairly quiet amps. Try switching V1 and V2 to see if it gets quieter. I'm guessing that a worn tube in V1 is humming. When you kick in the Fat switch, the gain of the second stage of V1 is increased, making the hum louder.

 

[Wally]

What does the amp sound like with nothing plugged into it?

 

[Joey]

Also try plugging the amp in another room or outlet.

 

[Ronsonic]

Is it really hum or is it more like shhhhh?

Hum is bad almost always, less bad if the controls affect it. Much less bad if it goes away when you've got a guitar plugged in that is turned all the way down.

Shhhhhh is almost inevitable. Gain makes noise.

Either way, BillM has your next diagnostic step. Swap those tubes.

 

[Tele-Champ]

I bought a used MIM Blues Junior (from a craigslist equivalent site) today. I noticed a significant hum even at bed room volume. This is my first tube amp, but I'm aware that tube amp does have some hum.

The hum has these characteristics:
- NOT related to the reverb amount
- worse after pressing the fat switch
- the hum is constant. NO popping or rattling type of sound
- starts to be audible at master=3 volume=3
- hum is significant at master=6volume=3, or master=3volume=6]

I tried out a used Blues Jr. at GC the other day and had every intention of buying it (@ $300) until I noticed a hum when I got the master volume knob up past 4... I could not get rid of that hum (although no hum under 4)...
So the sales guy comes over and he actually admitted that he heard the hum, too (normally they can't "hear a hum" (ha...) - Anyway, I passed on this particular Blues Jr. ..

I'm still wanting one though - even though I have a Hot Rod Deluxe and a '69 SF Champ. But I just hope this isn't an issue with used ones - - I played a new one and no hum, but I didn't want to fork over the 5 bills for the new one. I think they're overpriced as it is..

However, I see GC and Sam Ash have a sale coming up, with new ones going for $400 w/ coupon and discount, so I may have to think about that...

 

[1977CJ5]

I had one, which I let go a couple of years ago. I am really picky about amps that hum, hiss, or make any background noise. The one I had was extremely quiet. Bet you have a bad tube.

 

[tombstone blues]

+1 bad tube

 

[xjimmyleungx]

thanks everyone for the great advice!

I tried Billm's method. The hum is now softer and acceptible, but it's still there. When unplugged, it is silent even when both knobs are at max. When plugged, it's still audible and it's worsened by the fat switch. I guess the tubes really needs to be changed!

BTW, it was a terrifying experience to manipulate tubes for my first time. I left it sitting there unplugged for 1 day before I dared to touch it. Plus I used 2 t-shirts to cover my right hand, while I strictly follow the 'one hand rule'. Hilarious!

 

[Billm]

There's no danger of shock from tubes unless you somehow manage to touch the pins while they're still partially engaged in the sockets.

When you turn off an amp that's been warmed up enough to play through, it self-discharges in 30 seconds or less.

 

[Wally]

I am starting to suspect that this is a ccase of single coil hum being amplified naturally by an amp. IME, when there is no hum with nothing plugged in, the 'hum problem' almost always rests with the instrument. What guitar or gutiars are you useing? DOes this hum exist with single coils only or with humbuckers as well?

 

[Ronsonic]

thanks everyone for the great advice!

I tried Billm's method. The hum is now softer and acceptible, but it's still there. When unplugged, it is silent even when both knobs are at max.

If it is silent when unplugged it is NOT an amp problem. The noise is coming from your guitar or cable. Almost certainly the guitar since it changes with relative position.

BTW, it was a terrifying experience to manipulate tubes for my first time. I left it sitting there unplugged for 1 day before I dared to touch it. Plus I used 2 t-shirts to cover my right hand, while I strictly follow the 'one hand rule'. Hilarious!

Far too much fuss. Unplug the amp, let it cool, reach in and change the tubes. Don't grab the pins while they are still in the socket. It is almost unimaginably difficult to shock yourself that way, so relax.

 

[xjimmyleungx]

Thanks Ronsonic and Wally. Unfortunately I only have 1 guitar, so i have to test it with another guitar later when a frd visits or something.



What does this thing do and how do I put it back on? This thing gets attracted (magnetically) to the speakers automatically, and the strip of black sticker seems to be not sticky anymore.

image removed

 

[Billm]

The grille just keeps your fingers away from the hot tubes. There's no need to reinstall it unless you have a young child (or incredibly stupid adult) who can't resist touching the pretty glass thingies.

 

[Telenut62]

My tube amp was noticeably hummier one day, had me freakin out....then by trial and error I worked out it was one of the leads.....doh!! or phew....easy fix.