Hum on Tube Amp - Can't find source

@imhififan @ervikingo

Have you tried connect a different pair of speakers on your Manley Snappers?

Another good point. The manual states: Recommended Speaker Load: Optimized for 5 ohms

Do you know what impedance your speakers are rated ervikingo?

Once the noise starts you can’t bias them as the voltage cycles.

To me, this is the most concerning factor in this whole scenario.

Here’s a few other tidbits from the manual:

-For the power tubes in our amplifiers, after a few years if you notice a small revolt going on where several of the output tubes are misbehaving or getting hard to bias, you might consider doing a full re-tube.

-Three tube types that are electrically and plug-socket compatible with the 12AT7A dual triode include the 6021, 6679, and the ECC81 (I find it a little interesting that they made no mention of a 12AX7 here).

-Never operate the amplifier without a speaker load, or suddenly disconnect the speaker load while the amplifier is producing a signal. This risks punch-through of the enamel insulation covering the transformer’s internal magnet wire. Permanent damage to the output transformer may result 

-Additionally, it is best to cut power to the Snapper when not in use rather then leaving the power on indefinitely. This will enhance tube and system life.

 

imhififan @ervikingo

Have you tried connect a different pair of speakers on your Manley Snappers?

Another good point. The manual states: Recommended Speaker Load: Optimized for 5 ohms

Do you know what impedance your speakers are rated ervikingo?

Once the noise starts you can’t bias them as the voltage cycles.

To me, this is the most concerning factor in this whole scenario.

Here’s a few other tidbits from the manual:

-For the power tubes in our amplifiers, after a few years if you notice a small revolt going on where several of the output tubes are misbehaving or getting hard to bias, you might consider doing a full re-tube.

-Three tube types that are electrically and plug-socket compatible with the 12AT7A dual triode include the 6021, 6679, and the ECC81 (I find it a little interesting that they made no mention of a 12AX7 here).

-Never operate the amplifier without a speaker load, or suddenly disconnect the speaker load while the amplifier is producing a signal. This risks punch-through of the enamel insulation covering the transformer’s internal magnet wire. Permanent damage to the output transformer may result 

-Additionally, it is best to cut power to the Snapper when not in use rather then leaving the power on indefinitely. This will enhance tube and system life.

With the motorboating clue, it would not be unthinkable that those small tubes are involved.
Do these have coupling capacitors?

Something like a broken solder trace could easily be involved to create a situation where the amps is motorboating - maybe even from trying to account for DC.

@ervikingo 

I wonder if sending the tubes out to be tested might not be a bad idea?

TC Tubes

Desert Amplifier Repair