6F6 Stereo

The idea here is to design and build something useful, unusual, compact and not too greedy for power.

I've got a few American metal tubes of the 6V6, 6F6, 6L6 variety which, though less popular than the later glass versions, are decent valves with a quirky look.

To keep with the black minimalist look of these valves I've chosen a black drop through mains transformer from a McMichael wireless a black tar dipped transformer from a 1939 Philips wireless.  This set had an AZ1 directly rectifier (4V @ 1A header) and EBL1 pentode (6.3V @ 1.4A).  For output transformers I've picked a couple of tiny ones from Philips wireless sets - these were driven by EL41 pentodes so have the correct impedance when driving 4 ohm speakers, albeit at very lower power.

 

Why use 6F6 rather than 6V6?

It's my understanding that the 6F6 is a pentode, whereas the later 6V6 and 6L6 output tubes are both beam tetrodes.  It's also my understanding that pentodes are a better choice for single ended use.  Well a triode would be better, and any of these could be strapped as triodes, so that's something I might try later.

Possible circuits
Here's a rather complicated one using ECC83  (I'd use 6SC6) and 6V6. It's DC coupled, and has two negative feedback circuits - which is unusual.  

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