Harmonic Tube(s) with attenuator

[ENB]

Guys I have a friend who has a 45 Watt Dr. Z head. He is using a "Dr. Z Brake Lite" which is rated to attenuate amps up to 45watts. He is running the Z head between 6 and 7 on volume and is getting some serious harmonics associated with a low C note.

I had him tap test the tubes and he said the EL84s were quiet, V 2 is dead quiet but the V1 had some harmonic respose to the tapping. He is an experienced player and knows that the power soak works the amp and may shorten tube life a bit but I think he has recently started using the thing.

I have limited experience tinkering with tube amps thus far and have NO knowlege of the the end result or side effects of using the power soak.

Is this a problem in the amp, or is this common to using the load.

I dont know if he has dimed this think yet or not and if so, if it occurred then or not.

Thanks in advance for your advice.

Wayne AKA ENB

[hasserl]

Could be a preamp tube, the attenuator would have no effect on tube life for the preamp tubes; they seem to be able to go bad at about any time. If it's ringing when he taps it it might be the source of his problems. The easiest thing to do is to try swapping it out with a good tube and see if that clears up the noise.

[Chuck H]

+1 on what hasserl said. But keep in mind that if V1 is just making a tap or brief "bing" or "dunk" kind of sound when tapped this is probably normal. V1 is the most sensitive tube in the amp and it doesn't take much to make an audible noise come from it when the amp is turned up a little.

If it turns out not to be a preamp tube and the amp doesn't make the odd harmonic when the attenuator isn't being used then I would suspect the attenuator. From what I've read the Air Brake puts some very irregular impedance loads on the amp at different settings. Irregular enough that I wouldn't use it with my amp. This could cause the problem.

Chuck

[hasserl]

Good points Chuck, IIRC the Air Brake puts something aproaching 30 ohms load on the amp at full attenuation, the more attenuation, the higher the impedance.