Tube Amp Question

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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.

Gary V

[John Williamson]

On 05/04/2020 00:29, wrote:

> 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.
>

To put it simply, it has two output stages running in parallel, each
consisting of a pair of (hopefully) well matched tubes, both feeding a
single output transformer, with a centre tapped primary winding, which
has each half fed by one of each type of tube, with a mixer between the
pre-amp and the output stages to decide what proportion of the signal is
fed to each output stage.

The tricky bit is labelled "REBEL MIX MOD V2" on the copy of the
schematic here, and is, in effect, two balanced signal faders
mechanically linked so that as the signal fed to one stage increases,
the feed to the other one decreases. The arrangement is called a cross
fader.

--
Tciao for Now!

John.

[Phil Allison[_4_]]

wrote:

-------------------------
> 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