Concertina or Long Tail PI ??? - benefits and disadvantages respect each other ?

[kagliostro]

When planning for a new amp

which are the reasons to choose a Concertina or a Long Tail Phase Inverter ?

which are the benefits and disadvantages for each other ? 

Must choose looking to the kind of output tubes or to the power of the amp ??

Thanks

Kagliostro

[FYL]

The cathodyne is beautifully simple, it works great in small/medium amps, usually cathode biased with little or no NFB. It sounds best when not fully overdriven and should only be used with power tubes requiring reasonable drive.

Larger amps will use an LTP, with NFB and a presence control. Or two channels summed at the PI. Or... It can be designed for slightly higher gain, sounds smooth on the edge of OD and can drive big bottles.

[HotBluePlates]

But you wanted the reasons for what FYL was saying...

The cathodyne ... works great in small/medium amps ...

If you have a power supply of fixed voltage, the concertina/split-load/cathodyne will produce a smaller output voltage than a long-tail. That is because the supply voltage must be able to support 2x output signal swings (1 plate and 1 cathode) plus still have enough voltage across the tube for proper function.

The long-tail has an elevated cathode voltage, but doesn't have to support 2x full-size output swings.

Since the split-load delivers a smaller output voltage (to one side of the output stage) for a given supply voltage, it makes sense to use a tube whose bias is just equal to this smaller voltage. After all, output stages are usually designed to achieve their maximum power capability when the contro grid is driven just to 0v (peak incoming signal equals bias voltage).

Hiwatt noticeably breaks this trend. However, every other guitar amp manufacturer looked to the higher output voltage capability of the long-tail with a given supply voltage when trying to drive bigger tubes. This was not necessarily true of hi-fi manufacturers for a variety of reasons.

[kagliostro]

Many Thanks FYL & HBP

Kagliostro

[echuta13]

Orange also used the split-load in their designs.  The MarkII comes to mind & that was driving a quad of EL34's.