Another red plating tube question

[Eminence1963]

One of my tubes red plated this morning had a buzz in the right speaker. I'm new at troubleshooting so my question would be swap the tube out and turn this amp back on and cross my fingers that it was just a tube or before I turn it back on and replace that tube check something further in the amp that might cause that particular tube to Red plate? The amp in question is a 25 watt per Channel push pull fixed bias amp. I did pull the bottom cover off the amp and did not see any of the capacitors leaking nor did I notice any of the resistors burnt. This is all done by visual inspection nothing on the circuit boards looked out of place. All the wiring looks intact. I am not sure how long the tubes have been in this amp as I have owned this amp for the past 3 years, bought it used run it every day for at least 8 to 10 hours. Never run the amp hard just a normal volume level background listening music mainly. There are no fuses inside this amp the only fuse that is on this amp is the main fuse to the power cord. Fuse never blew.,
The amp in question is a Shuguang I25.

 

[gadget73]

Move the tube and see if the problem moves with the tube or not. If it goes with the tube, you need a new one. With that much use you may just be due for a new set. Even assuming just a 40 hour week, you're at some 6200 hours of use, which is not insignificant for power tubes.

If the problem stays with the position, something in the amp is unwell. Might be as simple as a dirty or loose socket, or something more complicated.

Also worth checking the bias if you haven't.

 

[Eminence1963]

Move the tube and see if the problem moves with the tube or not. If it goes with the tube, you need a new one. With that much use you may just be due for a new set. Even assuming just a 40 hour week, you're at some 6200 hours of use, which is not insignificant for power tubes.

If the problem stays with the position, something in the amp is unwell. Might be as simple as a dirty or loose socket, or something more complicated.

Also worth checking the bias if you haven't.

Should have said Cathode BIAS amp. Got to buy some cheap test tubes first, as I don't want to fry another Shuguang Black Bottle 6CA7 tube. Thank you for the reply.

 

[primosounds]

One of my tubes red plated this morning had a buzz in the right speaker. I'm new at troubleshooting so my question would be swap the tube out and turn this amp back on and cross my fingers that it was just a tube or before I turn it back on and replace that tube check something further in the amp that might cause that particular tube to Red plate? The amp in question is a 25 watt per Channel push pull fixed bias amp. I did pull the bottom cover off the amp and did not see any of the capacitors leaking nor did I notice any of the resistors burnt. This is all done by visual inspection nothing on the circuit boards looked out of place. All the wiring looks intact. I am not sure how long the tubes have been in this amp as I have owned this amp for the past 3 years, bought it used run it every day for at least 8 to 10 hours. Never run the amp hard just a normal volume level background listening music mainly. There are no fuses inside this amp the only fuse that is on this amp is the main fuse to the power cord. Fuse never blew.,
The amp in question is a Shuguang I25.

Yeah, when they red plate the speaker of that side will frequently emit a loud buzz or hum. Once a tube red plates like that it is certainly not going to be the same and probably indicates that the rest of the tubes are ready to be replaced if they all appear to have been part of a quad. If you want to be double sure of no problems , and since your amp is chi-fi, it would be best to put the amp on a variac and measure the bias voltages on the power tubes and check if the coupling caps have any DCV on them which would indicate that there is dc leaking through them. With the variac you can run the amp at 80% of wall voltage which should keep you out of red plate territory and do the voltage checks.

 

[Eminence1963]

Yeah, when they red plate the speaker of that side will frequently emit a loud buzz or hum. Once a tube red plates like that it is certainly not going to be the same and probably indicates that the rest of the tubes are ready to be replaced if they all appear to have been part of a quad. If you want to be double sure of no problems , and since your amp is chi-fi, it would be best to put the amp on a variac and measure the bias voltages on the power tubes and check if the coupling caps have any DCV on them which would indicate that there is dc leaking through them. With the variac you can run the amp at 80% of wall voltage which should keep you out of red plate territory and do the voltage checks.

Guess its time I get a Variac if I plan on fixing my own tube amps

 

[ToxicTele]

I picked up a cheap variac on amazon ( $50) and it serves the purpose. One thing I did do before actually using it was hooked my voltmeter up to the output and made sure the dial was putting what it said. long story short - the dial was way off. When I set the dial to 115 volts, my meter said 130 volts. It said this on two different voltmeters. So I basically made a new dial with my own gradations. This way I am certain of the voltage. Just my two cents.

 

[Eminence1963]

I picked up a cheap variac on amazon ( $50) and it serves the purpose. One thing I did do before actually using it was hooked my voltmeter up to the output and made sure the dial was putting what it said. long story short - the dial was way off. When I set the dial to 115 volts, my meter said 130 volts. It said this on two different voltmeters. So I basically made a new dial with my own gradations. This way I am certain of the voltage. Just my two cents.

Thanks for the heads up