• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Recommendations for PP EL84 circuits

But how would the GNF loop work with a valve of lesser gain?
You'd have less loop gain available, for a given closed-loop gain. I haven't done any calcs but my guess is you'd end up with a bit more distortion overall (because most distortion comes from the output stage), and definitiely higher output impedance. But if you're one of those people who likes the idea of 'low-feedback design' then go for it, it's a very forgiving topology.
 
Sample simulation.

6SN7, 6SN7, EL84 PP.jpg
 
Hi @andyjevans , I gather you are a fan of the 6SN7.

I was wondering if you had tried any of the 6SN7-oids that have a similar vintage? I have acquired a few 6SR7G tubes, which is close to half a 6SN7, but there are also Loctal equivalents. Many of the alternatives are relatively cheap, but a Sylvania 6SR7G is going to be the same standard of workmanship as a Sylvania 6SN7 in my books, so potentially bargains?

6SR7:

Skärmbild 2025-05-07 121310.png


6SN7:

Skärmbild 2025-05-07 121344.png