Clean Tone from 5E3 - Explanation ?

[vjf]

Can you 5E3 experts explain to me why I get a very clean tone and drop in volume from my 5E3 when I have it set up this way?

Plugged into Bright 1
Bright 1 Volume = 3
Normal Volume 12
Tone 12

Please refer to the schematic attached when explaining.

[loudthud]

When the Normal Volume is at 12, the output of the Normal preamp triode is connected to the grid of V2. This looks like a .1uF cap in series with the parallel combination of the 100K plate resistor and the plate resistance of the Normal preamp tube (RCA tube manual says ~23K for a 12AY7).

Because the Bright channel's Volume is at 3, the signal must go through more than 900K to get through to the grid of V2 (assuming a log volume control). So there is an attenuator set up with 900K in the series leg and about 20K in the shunt leg. This attenuates the signal from the Bright channel something around -33dB before it gets to the grid of V2. Turning down the Normal volume control to 9 will raise the impedance at the grid of V2 to about 500K so now the attenuation is around -9dB. Much louder.

[vjf]

Thanks loudthud.

In somewhat layman's terms, I think you are you saying that with the Normal channel's volume at 12 I'm losing some signal to ground and by dropping the Normal volume to 9 (effectively adding resistance) the signal loss to ground is now less and hence louder? Maybe this is not technically correct but it helps me understand this better.

Any explanation for the need to have the Tone at 11 or 12 to complete this clean setting? If I remember correctly, anything less than 11 on Tone knob and the 5E3 is not as clean.

[loudthud]

The 5E3 originally was a pretty low budget amp. Certain compromises were made in the circuitry to keep the cost low. One of the consequences of this is the interactive volume controls. The tone control also interacts with both volume controls. It's all part of the "charm". Leo Fender never thought anyone would actually operate the amp with the volume on 12.

There are many mods that have been suggested that remedy the interaction and you'll find many of them here if you search long enough. Bruce (Mission Amps) has a pretty cool mod kit he sells that gives you a dual pot for the tone control so the tone works on both channels.

One big weakness of the 5E3 is the poor control of volume at low (clean) levels. The volume goes from nothing to too much between 1 and 2 and is as loud as it can get by 3 or 5. Although it's not a dual channel, I like the 5D2 preamp and controls. A little bit of gain is sacrificed but you still have a treble boost at max volume. Then I use the third pot as a bass control. Check this thread: http://music-electronics-forum.com/t11171/