#1
So I've got my valve junior built in a cookie tin and I was playing it cranked, then I saw a decent sized arc at the base of the el84, I'm not sure if it was inside the tube or behind it. A quick google gave me that it could be inside the tube or across the tube socket but I don't see any burn marks across the socket.

The speaker being disconnected is out of the question, I checked all the connections for it and the speaker hasn't cut out.

I had been noticing some static popping while it was on but not in use. I thought that could have been from my terrible lead dress but I'm having second thoughts about that.

So whats the most likely cause for this? And how do I go about solving this problem?
Guitars:
LTD F-50
Yamaha EG-112
'77 Harmony
Roadworn Starcaster
Gretsch G5120

Amps:
Vypyr 15
Epiphone Valve Junior combo
#2
may i be the first to suggest you don't build amps in cookie tins????
Belief is a beautiful armour but makes for the heaviest sword.
#5
Power tube is probably dying, you need to do a screen grid resistor mod.
Valve jrs are bad about killing power tubes.
#6
may i be the first to suggest you don't build amps in cookie tins????


Try telling that to Cathbard, I'm fairly sure it didn't arc because of the cookie tin.
Guitars:
LTD F-50
Yamaha EG-112
'77 Harmony
Roadworn Starcaster
Gretsch G5120

Amps:
Vypyr 15
Epiphone Valve Junior combo
Last edited by grungebaby at Aug 22, 2011,
#7
Quote by SMTHSCN
the tin is almost definitely made from a conductive metal dude.

mystery solved.


So is the stock Valve jr chassis.
#8
Quote by mcamp1230
So is the stock Valve jr chassis.

and 100% of amp chassis I have ever seen our bought :p
Epiphone Les Paul Plus Top
Jet City JCA5212RC (SLO Modded)
Ibanez WD7 Wah
Mad Professor Sweet Honey Overdrive
TC Electronic Flashback Triple Delay
TC Electronic Trinity Reverb
#9
Yeah, there's about 3/4" of clearance between the chassis and where the arc could've been so it probably wasn't that.

The power tube is probably over a year old, I can't remember when I got the amp, I haven't ever changed it and I don't have any other tubes but I really don't want to blindly change it and have it really fry something.
Guitars:
LTD F-50
Yamaha EG-112
'77 Harmony
Roadworn Starcaster
Gretsch G5120

Amps:
Vypyr 15
Epiphone Valve Junior combo
#10
Quote by grungebaby
Yeah, there's about 3/4" of clearance between the chassis and where the arc could've been so it probably wasn't that.

The power tube is probably over a year old, I can't remember when I got the amp, I haven't ever changed it and I don't have any other tubes but I really don't want to blindly change it and have it really fry something.


Any el84 will work. JJ's and Mullards are nice.
#11
I meant I don't want to replace it then it not be the tube dying, like I don't want to have a circuit problem and think its a tube then turn it on and have a cookie tin full of smoke
Guitars:
LTD F-50
Yamaha EG-112
'77 Harmony
Roadworn Starcaster
Gretsch G5120

Amps:
Vypyr 15
Epiphone Valve Junior combo
#12
Quote by grungebaby
I meant I don't want to replace it then it not be the tube dying, like I don't want to have a circuit problem and think its a tube then turn it on and have a cookie tin full of smoke


Oh...I had a similar thing happen with mine, it was a blue spark in the power tube and it died shortly afterward. It also fried r10 in the circut.
#13
I've seen some arcing between the screen grid and cathode before.


If you don't see any burns on the tube socket, top and bottom, check to see if you can put another tube in there. This seems similar to a time I had a guy tell me a tube arced. He said that the amp had a ticking noise and then boom, the tube was gone. We found out that the screen grid was arcing slightly before it went completely.
#14
Well theres no burn marks or anything so I guess I can assume that its the tube and I'll try and get a replacement asap.
Guitars:
LTD F-50
Yamaha EG-112
'77 Harmony
Roadworn Starcaster
Gretsch G5120

Amps:
Vypyr 15
Epiphone Valve Junior combo