Blues Junior Help!!

Gwatkins15

I have a weird buzz/vibration/drone noise, see videos, on my blues junior. I recently changed the power amp valves to a matching pair of JJ EL84's. There's no noise when playing with the master around 2/3, but it starts at 3+.

-I've tightened every screw
-Checked valve seating
-Removed reverb tank
-Removed chassis 
-Removed chassis and speaker
-Tried with a different speaker/different guitar

...and it's still there! Anyone have any ideas? Anything to look for?


I'm rolling off/on volume in the videos

ICBM

If it wasn't doing it before you changed the valves, try putting the old valves back in - that will either eliminate or confirm them (most likely just one of them) as the problem.

Gwatkins15

I've only started playing it at gig volume the past few days, so I threw the old valves out, thinking it was okay at home volumes... So I've stupidly thrown them out.

Worth saying the old power amp valves was replaced because it suddenly lost power and had a purple lightning show in one valve.

ICBM

That was a good reason to throw that one out . The other one may have been OK.

Try tapping on each of the power valves with the amp on and see if you get a rattle or crackle - you'll have to take the back panel off to get at them easily, so be careful. If it is a valve problem it's common for it to be so vibration-sensitive that you will often get a noise even when tapping the other valve, so hold the one you're not tapping with a cloth.

It's also possible that the dying valve damaged something on the PCB above it, which is quite common on Blues Juniors unfortunately...

Gwatkins15

No noises from tapping on the valves. I've had a look at the circuit board and all the solder joints look clean etc. 

Is it worth trying another set of valves? 

DJH83004

I've had Blues Juniors in the past exhibiting similar symptoms which turned out to be a failed power supply cap, (usually the pre-amp cap, the last 22uf / 500v to the right of the bank of three). May not be the case, but it does sound familiar, almost a very exaggerated ghost noting.     

Gwatkins15

It only happens when turned up, and is more pronounced on the lower strings. I'll have to get a decent multimeter to check that, so I'll see if it's something else first. Thanks both.

Gwatkins15

New power amp valves haven't made a difference. I have found that the solder points on the valve socket circuit board do move lift when I wiggle the valves. This is on the power amp side. I think it's mainly on the points without tracks, are these unused?

I am getting a slight burning smell with both sets of valves too. 

ICBM

Gwatkins15 said:

New power amp valves haven't made a difference. I have found that the solder points on the valve socket circuit board do move lift when I wiggle the valves. This is on the power amp side. I think it's mainly on the points without tracks, are these unused?

Yes, but make sure there aren't any - even barely visible - cracks in any other the others. It's probably worth re-soldering all of them if you aren't sure. This is quite a likely cause of the problem if it's not the valves.

Gwatkins15 said:

I am getting a slight burning smell with both sets of valves too. 

This is fairly normal with BJs, they run too hot. You can help it a little by reconnecting the power transformer for the correct 240V UK supply rather than the 230V Euro-fudge as Fender (legally have to) supply it.

To do this, locate the white/black striped wire which comes from the bundle of wires on the transformer and goes to the power switch, and the black wire which goes to P6 on the PCB. Swap these. (You may need pliers to pull the connector off the PCB, they're usually very tight.)

Corvus

I can't remember the exact buzz/noise my lad's one made so this might be a red herring, but one or two filter caps were leaky. I'm no tech but it was easy to see the gack oozing from them where the wire exits them.

Gwatkins15

Resoldered sockets and re-tensioned, still buzzing, not sure if it's slightly less or if it's just me. Caps all look ok, no leaks at all. Power wires swapped too. 

Definitely gets worse with the fat switch on, without the fat switch it's not that loud and I could live with it, but then the sound is flat.

I do have loads of buzz with different guitars (both shielded and wiring checked recently), earth connectors in the amp look okay though.

ICBM

This should probably have been my first post on this thread...













Throw it off a high building and then go and buy a Hotrod Deluxe.

jpfamps

Might be oscillating ultra sonically. Easy to diagnose with a 'scope.

Try pushing the ribbon cable to the power valves away from blue wire from the output transformer.

Roger

What about these I had some vibration issues with an old laney cub. It was down to having the valves so close to a 12 inch speaker in a small cabinet and these helped - think I found mine on ebay

DJH83004

With regards to the valve sockets, you need to scrape the lacquer off the tracks quite far back from the soldered joints to expose the copper and make sure the solder flows fully over the track. Even though the power supply caps look OK that would be my next port of call.    

Gwatkins15

ICBM said:

This should probably have been my first post on this thread...













Throw it off a high building and then go and buy a Hotrod Deluxe.

I have... well a deville anyway!   https://imgur.com/a/cgSlo

So... for £40 I've brought a tested pcb, with all metal jacks, valves, bias mod, that all works. Sod it.

ICBM

That's not a bad solution. I've done that in the past when I had one with substantial lower board fire damage, which is another characteristic of these amps...

The Rat Mods chap sells them off sometimes after he's rebuilt one.

NPP

apologies for going off on a slight tangent - given that these amps don't sell for very much used would there be a point to just using them for a project, say to house an amp kit? 

I'm not really happy with mine but can't be arsed to sell it either because it doesn't seem to be worth more than a good pedal. 

Gwatkins15

ICBM said:

That's not a bad solution. I've done that in the past when I had one with substantial lower board fire damage, which is another characteristic of these amps...

The Rat Mods chap sells them off sometimes after he's rebuilt one.

The Rat mod man is who I've used, I'll see if he wants my circuit board and get some money back. Thanks for your advice, hopefully I won't post on this thread again..

ICBM

NPP said:

apologies for going off on a slight tangent - given that these amps don't sell for very much used would there be a point to just using them for a project, say to house an amp kit? 

I'm not really happy with mine but can't be arsed to sell it either because it doesn't seem to be worth more than a good pedal. 

One of the problems with them is that the cabinet seems to be inherently 'wrong', in that it doesn't sound good with any speaker. But if you can live with that, the chassis or the cabinet are a fairly good platform for a project.

The Session Blues Baby is designed to be a drop-in fit, for one...

jpfamps

If you install a used board change the 47 pF cap across the phase inverter for a 220 pF 1 kV cap (from memory this is C9).

This will make the amp stable and prevent oscillation in the future.