Redplating again.

[richard parker]

I tried swapping the output tubes in my Roadhouse around and thought I had identified the problem as one of the tubes. However, when I put the new tubes in one of them redplated. I've read that once a tube has redplated it will continue to redplate. Is this correct ? I only ran the new tubes until I could see one of them start to redplate and immediately switched it off.

 

[misterwhizzy]

Re: Redplating again.

I don't think that's the case. Let's take the case of a very hot bias. You could get the tube to redplate without anything being wrong with the tube. You adjust the bias, it stops, and it's fine for a long time. So I could see it being something other than the tube itself having an issue.

 

[MetalManiac]

Re: Redplating again.

Join this forum; the Ampgarage. Youve got to be polite- those people are electronic aces, and are nice, but don't have a lot of patience with amateurs sometimes. Redpalteing can kill a tube immidiatley, although if you are lucky the tube should will still be okay to use. As long as your amp didn't pop or smoke you are still dealing with minor issues likely, and the tube could still be good. Again, your amp needs service by a qulaified tech, but i already suggested that to you to no avail... quit with the swapping tubes already. A tube never redplates unless theres a problem with your amp, it just dies and/or fries your amp when doing so.Keep on messing around with that amp buddy,when you have no earthly idea what you are doing, and you'll fix it for good allright; maybe take out an output transformer.

 

[Chickenwings]

Re: Redplating again.

i still reckon its one of the screen resistors as per your previous redplating enquiry. Have you checked them?
Easy to check - just open up the amp and look inside. They are the ones that sit across the top of the tube sockets. If one of them is toast it will look like its burned out, or cracked. IN some cases it does not show any outward signs of burnout, so if they all look fine, drain your filter caps and run a multimeter across them to make sure they are the correct resistance and not infinite resistance (i.e. shorted). They are usually 470ohms, but i dont know what value it would be in your cornford. They often get cooked cos they sit on top of a hot tube, and heat rises.

a toased one might look like this:

or depending on the type of resistors used in your amp, and its construction (the next pic has them mounted on a PCB) a toasted one might also look like this:

The fender hot rode series amps for example are notorious for this happening on the pcb.

If one is toast, its worth upgrading the resistor to one of the big higher wattage ceramic ones (3watts or 5 watts) and set them so they do not sit directly above the tube.
The pic below is a lovely repair/replacement/upgrade job:

 

[misterwhizzy]

Re: Redplating again.

Minor gripe. A shorted circuit is zero resistance. An open circuit is infinite.

 

[richard parker]

Re: Redplating again.

With the help of a great guy on the BK forum I identified the problem. He said ' It looks to me most likely that you have a poor contact with grid pin and the socket, and you may need to retension the pins in the socket. '

He was right. No more redplating.