Help !!
I am at my wits end
just finished repurposing a project amp
turned it into a rocket
but the #1 power tube keeps redplating
I have tried different PS cap, 100 ohm resistor, disconnected
the 1k5 resistor tried different tubes and even another socket
still keeps running away
not sure what to do next
thanks in advance
You do not have the required permissions to view the files attached to this post.
Theres a lot of residue on that socket, what is that? Does it red plate as soon as you take the amp off standby? Or once you start playing? When you say different sockets did you actually replace the socket?
Calculate your bias. You could simply be over the maximum plate disspation.
One tube can effect the tube next to it on the same PP side. What I am saying is that it may not be what you call socket 1, it could be your socket 2 or tube 2. But you must check where your bias is first, as Littlewyan said above.
What is the brown poo under your enormous screen resistors?
The poo is silicone
It was thAt way before I started on the amp
I purchased the amp from eBay
It was a two channel amp with reverb
The guy said one channel worked and one was noisy
But when I got it neither channel was functioning
So I stripped the board and turned it into a rocket
The power tube section was left alone
It also had a half powered switch that I removed trying to fix
The runaway tube
the problem was present before that socket was replaced
so I don't believe the condition of the current socket is an issue at this time
I tried the amp with a 5Y3 rectifier tube and I was able to play it for a bit
you could see just a faint red glow from that one power tube
with 5Y3 :
B+1 = 231 v.
B+2 = 228 v.
B+3 = 178 v.
B+4 = 158 v.
B+5 = 155 v.
all tubes are getting bias voltage 10.5 v.
in standby :
EL84 :
pin #2 = -.720 v.
pin #7 = -.9xx v.
pin #9 = -.9xx v.
the xx means the voltage was fluctuating slightly
the amp with 5Y3 sounds pretty crappy I am guessing because of the bad bias issue but it works
originally the amp came with a Weber copper cap rectifier
with that copper cap the tube begins to glow in about 1 minute
so I don't dare try and play it
Yer sorry the Standby Voltages on the valve are useless in this amp.
Now something is a bit off as you should have nothing on Pin 2 as thats the control grid pin. Odd that pin 3 is so high with pins 7 and 9 being low. Pin 9 should be lower than Pin 7.
Pins 2 and 3 definitely aren't touching? Have you got the Screen Grid Supply and OT Centre Tap connected to the correct supplies?
the OT center tap is on thew third cap
you can see in the pic
the first two caps are parallel
the screens are on the third cap to the right
its the green wire
and the choke is between those
its the thin red wires
