Power tubes glows red

[vatch23]

Hi, in a couple of my amps, one of the four outputtubes the plates starts to glow red after half an hour. Just one, and I replaced gridresistors and biased them down as far possible. Example: Guyatone ga1100 4x6L6 ,gridresistors 470R and 1K5 replaced...........485V on plates and bias down to -65V, this still happens. Please help me.

[loudthud]

First step would be to move the tube that glows red (mark it somehow) to a different socket to determine if the tube is bad or there is some problem within the amp that causes any tube in that socket to glow red. Could be as simple as the socket does not make good contact with the tube.

[Chuck H]

+++
Most likely a repair issue. Biasing the amp colder will only make the other tubes operate worse and sound bad. It's most likely a bad tube, a contact fault due to oxides on the tube pin, socket or both, or a bad board connection for that socket.

As mentioned,swapping the tubes around to see if the problem follows the tube or the socket is the first step to fixing the problem. And it may be different for different amps.

Be sure to bias up more normal once the problem is fixed so you can properly enjoy your amps.

[vatch23]

I did move tubes around on the Guyatone, it goes with the socket, where I did replace gridresistors and which has a biasvoltage of -46V. Now 450 on plates. Schematics here:

[Gtr_tech]

Check the grid stopper (1.5k), its solder connections, and the socket pin #5 for good grip on the tube pin.

[vatch23]

Ah,thanx all, I replaced the socket itself, and now this amp is Ok. Still dont know if it was a bad soldering joint or the socket itself that had bad connectors. This was my first post, and I realized I should have changed socket right away. Stupid. Now try to find out what the biasvoltage should be originally, -46 sounds OK, but has no real output.