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Re: Too much gain: please explain some things

Posted by Chris O on January 18, 2007 at 11:23:27

In Reply to: Too much gain: please explain some things posted by Frihed89 on January 18, 2007 at 00:45:06:

1. How loud is loud? When you "turn the volume up" with the 5751 are you at higher output volumes than with the other input tubes, 6414 etc.?

With the 6SN7 in the output being driven by the 5717 and by the 6414 with the same output volume to the headphones, does the 5751 crackle and the 6414 sounds quiet? If this is the case, you likely have a problem with the 5751 not the 6SN7. It could be that the load presented to the 5751 at higher levels is too much for the tube.

2. When a tube amp says thay you can use all sorts of tubes in the circuit, it really might be optimized for one set, but allow substitutions. Regardless of what the manufacturer says, there will be one combination of tubes that will operate best in this amp. Pick a combination that sounds good to you and stick with it.

Gain is the ratio of voltage out to voltage in. The 5751 has a gain or a mu of 70. The other tubes are lower in the 20 to 30 range. The gain of the preamp tube is not what is causing your problems. Both the low gain tubes and the 5751 can both put out a voltage gain of 10 which is probably all you are using. For you to take advantage of the full mu of 70, you would be deaf in a matter of minutes. This louder overall level could cause the output tubes to clip or distort. You would be listening a lot louder to the 5751 than the 6414 if gain was an issue. Tube rush and hum are other issues. Crackly noise at the same overall output levels indicates an unhappy 5751.
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