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Glowing Output Tube Trouble
By Gary | January 13, 2008
Here’s a video I saw on YouTube that is interesting by mistertonemaster. He took the time to capture a glowing output tube on tape. These come in the shop sometimes. If you experience this in your amp, turn it off immediately and take it in for repair. Simply replacing a tube may fix the problem but you could have an open bias resistor.
What this means is the bias resistor acts as a gas pedal when the input signal hits the output tube. It’s usually biased as a negative voltage. If it opens from heat, wear and tear, pulls away from the circuit board, etc. This presents a 0 voltage to the input of the output tube. This effect causes the output tube to run wide open, putting a strain on your amp as well as the tube.
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Topics: amp repair (Fender) |
January 28th, 2008 at 9:54 pm
Gary,
I have a 1966 Fender Vibrolux. The vibrato is unreliable and the reverb channel has a fuzzy sound to it at higher volumes. The normal channel is fine. I switched the power tubes and it makes no difference. Perhaps there’s a foul preamp tube?
Does it harm the amp playing it loud (other than wearing out tubes faster and stressing speakers?). I play it at 5 most of the time and will turn it up to 7.
Any suggestions?
Regards,
Barrie
January 28th, 2008 at 10:02 pm
Hello,
First congrats on the amp,,don’t ever sell it, unless it’s to me :)
You can try the preamp and vibrato tubes…..just switch with the other tubes..but notice that the tube next to the reverb transformer is a 12at7..switch that with the drive tube..look at the tube chart in the cab or find one to look at
Just make note of what you’re doing before you do it…
also if you mean the vibrato is intermittent when you hit the switch..or turn the knob?
If it’s not the above you have problems
No it doesn’t hurt on those settings other than what you stated…you have to crank them to get the tone…
Gary