Name is Don and call sign is NC4XX.
I'm have a problem with my Clipperton L, Nothing new has been doing this since I had it. I'm getting a slight hum when amp is keyed trough my audio. Sounds like a ac hum in the audio. I've had the Harbac modes done on this amp. Some have said to change wire in the transformer.
Any help will be greatly appreciated!!
Thanks, Don NC4XX
Every Clipperton L made by Dentron hums. They hummed when new, they hum when old.
The reason they hum is Dentron never used a center tap on the filament transformer. They feed the filament return from the bias and relay system from one side of the filament winding, instead of the center.
This puts about 20 volts peak to peak ripple on one side of all of the filaments, and this biases the filaments off and on. The result is an AC biased intermodulation product generator. One pin and one side of the filament has bias + (6.6 * 1.414 = 9.3 volts) positive, and then bias - (-6.6 * 1.414 = -9.3) on the other swing. That ripple effectively swings all the emission current to one area of the filament and back to the other side 60 times per second.
Back when the amp was first built, I asked the person who claimed to be the designer why he did a thing like that. He told me it was to keep the amp from oscillating on ten meters.
You might have another issue besides the built in factory hum generator, but every Clipperton manufactured, unless modified in the field, has some amount of built-in 60 Hz hum from the factory.
It also has too much filament voltage, not that reducing voltage will make Chinese tubes last any longer. If you correct the missing center tap, you might want to think about correcting the filament voltage. It really won't make the tubes last longer, but it will be more comforting to know 6.3 volt tubes are running closer to 6.3 volts. :-)