[Phil Allison[_4_]]

wrote:

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I have a Egnater Rebel-20 guitar amp head which is very versatile along with some nice features: multi-tap output transformer, effects loop, built-in attenuator, master and gain knobs. One interesting feature which the manual claims is unique to Egnater is a "Tube Mix" control. This amp has 2 pairs of output tubes: EL84's and 6V6's. The Tube Mix control allows you to send the output to either pair or an adjustable mix of the 2 pairs. It's actually quite interesting to adjust this knob with different guitars, effects and cabinets.

With my basic understanding of how tube amps work I would have to guess this is quite a clever design. I found a schematic on the web but it wasn't clear to me how this feature is implemented. Any comments on how this was done? I'm just curious.


** Think I had one on the bench a while back.

The output stage consists of 4 tubes in parallel push-pull - EL84s and 6V6s are similar enough to work in place of each other.

Bias and grid sensitivity is about the same - both were designed for use in radios with the minimum of drive need to get full output.

The Rebel 20 simply allows the user to send some or all the grid drive signal to one type or the other or both.

As another poster said, it is a "cross fader" arrangement much like that found in disco mixers so the DJ can fade from one source or turntable to another while both are running.

Bit of a gimmick really.


...... Phil