Switch between 2 different output valves

[Paulycoo]

Hello all,
I’ve built an Ampmaker n5x where you can use either a 6v6 or an el84 power tube. You can’t have both tubes inserted at the same time. I’d love to leave both inserted and switch between them. Could anyone point me to a schematic please?
Best regards from the uk
Paul

[sluckey]

Use a DPDT switch to select the cathode (yellow) wires.

[Paulycoo]

Thank you Slucky, is that it? I can just leave both output tubes inserted in parallel? I didn’t think it would be so simple. Thank you

[sluckey]

Both tubes plugged in...

[tubenit]

Sluckey,


That's clever. Sharp idea. I like it!


With respect, Tubenit

[Paulycoo]

Thank you so much for helping again that's wonderful
Cheers Paul

[JPK]

Neat idea. I have an amp with an EL84 that I put a parallel octal socket. Never thought to have separate cathode circuits and a switch.

[scstill]

My Egnater Rebel 20 has a front face dial that allows you to adjust the amount of EL84 and 6V6 you want.
Each set is configured in Push Pull. Very nice when you set at half EL84 and half 6V6
https://el34world.com/charts/Schematics/files/Egnater/Egnater_rebel_20.pdf

[st]

Do you have a PT that can power the heaters of both? "Can't plug in both" sounds like maybe you haven't.

[HotBluePlates]

My Egnater Rebel 20 has a front face dial that allows you to adjust the amount of EL84 and 6V6 you want. ...

Just a complicated master volume.

The challenge for the present amp-build is whether the PT and OT can support the current of both output tubes idling.

[Paulycoo]

I would love to know how to measure that current and then check the transformers. Barry from Ampmaker says there is no safe and fool proof way of doing what I want, or he’d have designed it in the n5x from the start.

[Soulfetish]

I like the idea of switching the cathodes in that it keeps it simple, and safe on the lower voltages. Generally, it isn't ideal to lift the tube from any ground reference. Particularly when you have floating electrodes with the screens and plates connected to a high voltage  supply.
I would suggest a slight modification, which would essentially accomplish the same thing by putting the switched tube in cutoff, rather than opening the cathode connection.

[Paulycoo]

Thank you so much for that,
So essentially the 100k resistor blocks the el84 while the 6v6 is selected via the switch and vice versa?
Thanks Paul

[sluckey]

The tube that has its cathode circuit switched open is totally cut off. No current flows thru the tube. The only current happening in that tube is heater current. Surely your PT can handle the extra heater current.

But if you are concerned about the extra heater current you can use a SPDT to switch off one or the other of the power tubes filaments. Downside is you have to wait for the tube to heat up. I like the cathode switch better.

[kagliostro]

+ 1 for the cathode switch

Franco

[Paulycoo]

Thanks for that yes I’m not concerned about the current ….I wasn’t aware it would be an issue at all…..
Thanks for explaining the 100k resistors added to your solution, I’m most grateful to everyone who’s helped me….
Cheers dudes I’m making it….I’ll let you know how I get on
Best regards Paul

[kagliostro]

It is a collauded way

see here what did Mesa on the Blue Angel, yes the Blue Angel is a PP not an SE but principle is the same



Franco