Rivera hundred duo twelve blows fuses

[stingray_65]

My step son has just acquired a Rivera Hundred Duo Twelve from an uncle who said it would blow fuses after a few seconds.
We replaced the fuse and let it idle to see what was wrong. At first it was idling along ok , but when he plugged his guitar in the 6L6GT *-edit- they are EL34's *started to red plate real bad and before he turned the amp off it actually started flashing “blue lightning” in one tube and then the fuse blew.
It seems to be a really nice amp and worth the troubles to fix.
Any ideas where to start with this?

link to schematic at schematic heaven:
http://www.schematicheaven.com/newam...a_r_series.pdf

thank you
Ray

[stokes]

It could be as simple as a bad power tube or tubes,or a bad component associated with the output.If it is just a bad tube,changing the power tubes will fix it,but if it is something in the circuit,such as a bad screen resistor,the new tube(s) could blow as well.Best to have it checked by a tech.

[defaced]

Does it blow fuses with all of the tubes removed?

[stingray_65]

I'll pull all the tubes tonight and give you a reply.

i wish i cold afford to take it to a tech, but bench time costs more than i can afford these days.

I'm hoping it is something i can fix myself and that i wont have to replace more than the couple of power tubes that redplated and maybe a couple discrete parts.

Thank you
Ray

[stingray_65]

been idling a couple hours with tubes pulled and its still going,

the power transformer warm, but not likehot, i can keep my hand on it indefinitly.


thank you
Ray

[stokes]

been idling a couple hours with tubes pulled and its still going,

the power transformer warm, but not likehot, i can keep my hand on it indefinitly.


thank you
Ray

That just tells you it is related to the output tubes,but we already know that.If it is a bad screen resistor or a bias problem it wont blow the fuse with no tubes,doesnt necessarilly tell if it is merely a tube.

[txstrat]

Tubes are not likely going down all at the same time.
Have you separated the blue flashing tube from the others and still know in which socket it was?
I'd put two of the other tubes back in two sockets (one on each side of the PI not using the socket of the flashing tube) an see if this changes something.
Just for testing this shouldn't do any harm on the OT due to mismatch.

[stingray_65]

Tubes are not likely going down all at the same time.
Have you separated the blue flashing tube from the others and still know in which socket it was?
I'd put two of the other tubes back in two sockets (one on each side of the PI not using the socket of the flashing tube) an see if this changes something.
Just for testing this shouldn't do any harm on the OT due to mismatch.

Damn thats just basic troubleshooting techniques and i failed miserable on that,

I was so freaked out when it happened i didn't pay attention as to what positions the tubes were in.

tommorow (monday) i'll take the tubes to have them checked. after that, i'll repaet the blue flashy tube thinggy and take better notes..

[stingray_65]

Against my suggestions my son went ahead and put all the tubes in.

he found the tube that redplates and it redplates in all positions.

he also pointed out that when the amp is on standby the tubes glow yellow orange as normal,

but when the standby is switched off the blue glow happens in all 4 tubes, but the one starts to redplate very quickly.

another thing he pointed out was that the amp would work some what when we had first plugged in his guitar , but now nothing, no pops or hiss or nothing.

[stokes]

Dont worry about the blue glow.If,as you say,one tube red-plates in any position,then the problem is that tube.I would suggest changing all the power tubes so you will have a new,matched quad.