Channel Switching AFTER the Phase Inverter?

[Dr Tony Balls]

Hi All,

A friend asked me recently if it would be possible to build a two channel amp where one is 5E3-ish and one is Pro Reverb-ish. Obviously on most two-channel amps the phase inverter is shared and thus the signal is blended before the PI. These two circuits, however, have very different PIs so sharing a common one would not be possible/reasonable. I'm wondering if this sort of thing could be done with a switch AFTER the phase inverters? Basically each preamp has its own phase inverter with a DPDT switch after that selects which channel goes to the power tubes. I'd probably place a coupling cap before and after the switch to avoid any DC on the switch but does that sound feasible? Any pitfalls i;m not thinking about?

[sluckey]

It's possible. Is it a good idea? I don't know. Makes me wonder why I've never seen it before. Give it a try and let us know what you think.

[pdf64]

But the output stages are rather different too, 5E3 being cathode biased with a saggy screen grid supply, Pro Reverb fixed biased with a stiff screen grid.

Then how about the reverb, I suppose he'd want that in the 5E3 too?

A request for a fx loop may not be long in the offing

[Dr Tony Balls]

But the output stages are rather different too.

I know, but those are details for another conversation. For the sake of discussion we can pretend the two amps I mentioned were an Orange OR120 and a Marshall 1959. The point is determining if there are pitfalls to switching in this location.

[sluckey]

For the sake of discussion we can pretend the two amps I mentioned were an Orange OR120 and a Marshall 1959. The point is determining if there are pitfalls to switching in this location.

Jumping from 5E3 and Pro Reverb to orange and Marshall is quite a jump! There are no pitfalls but you need to consider how you will switch the NFB. You'll probably need more than just a DPDT switch.

[Dr Tony Balls]

Jumping from 5E3 and Pro Reverb to orange and Marshall is quite a jump!

Ha....for comparison sake i'm just saying to focus on cathodyne vs LTPI and how to switch between the two of them.

There are no pitfalls but you need to consider how you will switch the NFB. You'll probably need more than just a DPDT switch.

Excellent point!