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Rivera knucklehead... Please help me.......

toolshed

Member
Messages
914
I have a rivera knucklehead k-100 head on a marshall jcm800 1960 cab.... I was jamming tonight and heard a pop.... I looked over and the amp shut off. I then smelled some electrical smoke, and checked the main fuse and then a fuse that was right next to it.... both were completly fine. I waited and tried to turn it own again and nothing...... It won't come on.... anyone got any ideas? any input would be greatly appreciated!!!!!
 

PRNDL

Member
Messages
498
Most likely your amp shorted and a resistor burnt out in the power supply or output section.
The fix is usually a cap job and fresh set of tubes, along with testing the resistors.
Sometimes you can see the burnt one, but not always.

This is the time to bring it to a good tech.
 

RussB

low rent hobbyist
Messages
11,165
Most likely your amp shorted and a resistor burnt out in the power supply or output section.
The fix is usually a cap job and fresh set of tubes, along with testing the resistors.
Sometimes you can see the burnt one, but not always.

This is the time to bring it to a good tech.
Other than bringing it to a tech, your reply is bogus on so many levels :jo
 

rockon1

Platinum Supporting Member
Messages
13,189
Sometimes a visual inspection of fuses isnt telling. I like to check them with a meter. Also sometimes amps have extra internal fusing. Be warned though do not go poking around inside without draining the high voltage from the capacitors that stay charged even after the amp is unplugged! If you have no knowledge in this area a good tech is probably your best bet. Bob
 

Apprentice

Member
Messages
33
schematic shows at least 5 fuses. unless you've got a reasonable idea of what you're doing, pop + smoke = time to take it to a tech. fuses usually blow for a reason.
 

toolshed

Member
Messages
914
schematic shows at least 5 fuses. unless you've got a reasonable idea of what you're doing, pop + smoke = time to take it to a tech. fuses usually blow for a reason.
I'm have another question, when i got the amp the pre tubes were all microphonic.... i changed them and wow the amp was bad ass.... I didnt change the el34 power tubes.... if a power tube is the problem, would that cause the amps on/off switch to not light up in the on positiion
?... I mean when i say it's not coming on... i mean ...nothing is working.... not even the light on the on/off switch......
 

TweeDLX

Member
Messages
3,756
I'm have another question, when i got the amp the pre tubes were all microphonic.... i changed them and wow the amp was bad ass.... I didnt change the el34 power tubes.... if a power tube is the problem, would that cause the amps on/off switch to not light up in the on positiion
?... I mean when i say it's not coming on... i mean ...nothing is working.... not even the light on the on/off switch......
If the light doesn't come on, it's more than just a tube. Even if you find a bad fuse and replace it, it blew because of another problem. Tech time...

Mike
 

toolshed

Member
Messages
914
THIS JUST IN.................................
HEY GUYS THANKS TO ALL WHO HAVE REPLIED..... here is the latest....

I went back to the rehersal space today and noticed in fact that the main fuse was blown (after placing it on a meter)..... when i replaced it and turned it on, i noticed that one of the outer tubes was not glowing...... i think i might have found the problem...
so i had an idea. I was reading online where some people pull two tubes on their amps to make the 100watt amps 50 watt amps so they can hit the sweet spot better. From what i read, they pull the outer two tubes....... any ideas or should i just order 4 jj el34s?
 
Messages
3,041
Pulling a push/pull pair sounds like crap, and the db drop is barely there, so it ain't worth it. Sounds like one of your heater filaments blew, shorted, and popped the mains fuse. Just get a quartet of new tubes and take it to a tech for a proper bias. Tubes are cheap, transformers are not.
 

toolshed

Member
Messages
914
yeah pulling those tubes didn't sound like a good idea...... I ordered a quad matched set of el34s..... hope that works!!!!
 

Trout

Member
Messages
7,551
The thing that bothers me was the smell of smoke. A dead tube might very well be the result of another failure. My advice is get it in to a tech for a good checkup/visual inspection, Retube & Bias.

Of course If you know how to do this, the tech might not be needed.

I would be very suspicious of a burnt screen resistor or a resistor in the power supply as well as possible cap failure.
 

rockon1

Platinum Supporting Member
Messages
13,189
THIS JUST IN.................................
HEY GUYS THANKS TO ALL WHO HAVE REPLIED..... here is the latest....

I went back to the rehersal space today and noticed in fact that the main fuse was blown (after placing it on a meter)..... when i replaced it and turned it on, i noticed that one of the outer tubes was not glowing...... i think i might have found the problem...
so i had an idea. I was reading online where some people pull two tubes on their amps to make the 100watt amps 50 watt amps so they can hit the sweet spot better. From what i read, they pull the outer two tubes....... any ideas or should i just order 4 jj el34s?
This is why I test my fuses with a meter. Its not always readily apparent. That said the amp may have had a shorted power tube and took out a screen resistor if smoke was let out. Bob
 

halorealm7

Member
Messages
4,559
Hey Michael,
Did you bias this amp when you first changed the tubes? I thought you just put a set of tubes in it....:BEER
 

toolshed

Member
Messages
914
Hey Michael,
Did you bias this amp when you first changed the tubes? I thought you just put a set of tubes in it....:BEER
It was biased with the el34s so i got a matched quad of jj's on order now.... I hope that will help it. I talked to an amp tech and he said as long as i got el34 to go back in it then it should'nt need to be rebiased. :worried
 

RussB

low rent hobbyist
Messages
11,165
It was biased with the el34s so i got a matched quad of jj's on order now.... I hope that will help it. I talked to an amp tech and he said as long as i got el34 to go back in it then it should'nt need to be rebiased. :worried

I call ********. For the cost of tubes you can have the amp serviced. You may need tubes, but you won't know until a pro looks over the amp.

My question is why do you seek advice, then ignore it and go your own route anyways?
 

Trout

Member
Messages
7,551
It was biased with the el34s so i got a matched quad of jj's on order now.... I hope that will help it. I talked to an amp tech and he said as long as i got el34 to go back in it then it should'nt need to be rebiased. :worried

Interesting,

I have seen a huge difference in bias requirements from matched set to matched set.
Does your tech feel that what ever generated the smoke healed itself as well?
You might get lucky and then again, might not.
 

toolshed

Member
Messages
914
I call ********. For the cost of tubes you can have the amp serviced. You may need tubes, but you won't know until a pro looks over the amp.

My question is why do you seek advice, then ignore it and go your own route anyways?
with one tube out, i do know that i can't run the amp with only three tubes. That's why i assume that since the tubes need to be matched, I would go ahead and order tubes...I was stating what the tech said.... I am still taking the amp in to have it looked at, but i need new tubes anyway.....but I don't have 54 dollars just to blow for an experiment!!!!
 

uberpict

Member
Messages
504
My K-55 had a burnt resistor which caused one tube to run hotter and took out a diode eventually. Tech fixed it up right and power tubes last many months of daily playing. Not Rivera's fault either, I suspect a previous owner hadn't biased tubes properly. You really need to take it to a good tech or even check to see if Rivera would work on it at a good price. They can mod them slightly at the same time pretty reasonably. Just saying
 




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