3 position half power switch

[JD0x0]

is it possible to wire a 3 position half power switch for a Ceriatone OTS
with the first position being full power, the second position engages half power only on the OD channel and the third is half power on both channels

thanks,
JD

[blues38pavol]

is it possible to wire a 3 position half power switch for a Ceriatone OTS
with the first position being full power, the second position engages half power only on the OD channel and the third is half power on both channels

thanks,
JD

Think that really depends on the switch. I have a 3 position half power switch that was used in my Boogie. It was connected to a Simul-Class power tranny and the switch just selected a different tap on the primary, sending 120 VAC to a different primary winding. So, if you are using just the switch to accomplish this, then probably not. Anyone else want to weigh in here?

God Bless,
blues38pavol

[Structo]

Which OTS do you have?

Two or four power tubes?

I suppose you must have the 2 x 6L6 or you probably wouldn't ask.


Dumble #124 has a 1/2 power switch that disables two power tubes.
( at least that is what I think the switch does).

But on a 2 6L6 that isn't possible.

Have you considered an attenuator?

[heisthl]

is it possible to wire a 3 position half power switch for a Ceriatone OTS
with the first position being full power, the second position engages half power only on the OD channel and the third is half power on both channels

thanks,
JD

Short answer - NO

Long answer - It's true you can use a switch to "turn off" 2 tubes in a 4 output tube amp but the impedance changes so you can't do it while you're playing and definitly not just when you are in OD mode.

There is a "fake" way to do less power by manipulating the PI voltage that could be used like your wish list. It would involve switching a high value resistor in line with the B+3 feeding the PI plate resistors, a 1watt 470k is a good value to try initially.

[JD0x0]

thanks for the info guys.

my OTS is the 2 6l6 version, i was thinking of a pentode/triode half power switch. im planning some modifications for my amp once i get a new speaker cab, right now im using a marshall 4x12 with greenbacks

[Structo]

Dumble #124 has a slider switch on the back to disable two of the power tubes by shorting the cathodes to ground.

But of course you can't disable one tube in a push/pull two power tube amp.

I don't know much about the pentod/triode switch thing but I did find this at the Tone Lizard.

[img:625:286]http://tone-lizard.com/images/Pentode-Triode_switch.gif[/img]

Speaking of 'triode mode', there is much confusion about the 'proper' way to connect the output tubes in a 'triode mode'. While you aren't necessarily really connecting the tube as a triode, my own preferred method is simply to use the Screen-Grid resistor already there. Quick, easy, and requiring only a switch and a little bit of wire, the modification works well. You need a resistance here because of the poor quality of EL34s available today, none of which can handle the considerable current that would be on the Screen Grid with no limiting resistor. Below is a simple diagram for achieving the modification. Amplifiers with four EL34s require a little more thinking, but switching can be accomplished with a simple DPDT setup as well. Of course you could also have only the outside or the inside pair of tubes on the switch shown below with a 100 watt Marshall, and this idea can even be further worked with a DPDT/Center 'off' switch for three way switching. An added safety feature here is that if the switch ever screws up, you'll just 'shut off' the output tubes.

[mlp-mx6]

Are you sure it connects the cathodes to ground to cut power? Aren't the cathodes already directly attached to chassis ground? Perhaps it grounds the grids instead? Or LIFTS the cathodes FROM ground?

[Structo]

On #124 pins 1 & 8 are not jumpered like a lot of 6L6 amps are.
So I'm not sure if this is a EL34/ 6L6 thing or not.

You can see what I'm talking about on the 124 schematic.

[mlp-mx6]

Right. Based on the schem and the pictures, the switch DISconnects the cathodes from ground to remove those tubes from the circuit.