Do not spend money on useless expensive tubes. 6M6 or EL3(N) are already known and this is the reason they should be avoided. I had excellent results with EBL1 which is a double diode pentode, but the pentode is electrically equivalent to EL3. Actually the RT branded I got from France are superior to the WIRAG EL3N all are using. Slimmer and less dry sounding, better extension on highs. It's true you will need to make a pact with the devil and start using adapters for european side contact socket but well... nothing is for free. When you will discover how good quality old european pentodes sound on UltraSonic amps, you will not be able to listen to something else. EL3 is a small baby and this is why it never really got me, but I have rediscovered it on input when I started to listen to the bigger boys in the family like EL6, EL50 (4654) or EL51. And after you get the adapters you will see that many pinouts are similar so in fact you need 2 types of adapters (with top anode and top control grid) and only make some smart wiring inside to allow usage of more types than one.In place of 6L6 in your DAC, you should give a try to 6M6 tubes (if you can find them) it is a direct replacement of EL3N / EL11 with EL34, 6L6 pinout
Let's see what Radiomuseum says about EBL1:
The EBL1 is an EL3 extended by two signal diodes. It was used in simple superhets without audio pre stage where the output section was directly driven from the diode detector, or in sets where the audio pre stage was combined with the IF stage (6F7, ECF1, ECH4) or with the tuning eye (EFM1, C/EM2) or also used in the 3-diode-circuit combined with the EBC3. [J.R.27Mar2003]
Later edit:
I'll explain a little bit the trick with the pinouts taking a screenshot from my plans for my future amp.
1) top cap control Grid adapters - can work for EL2/EBL1/EF* tubes with some careful wiring
2) top cap Anode adapters - can work for non top cap tubes and also for anode wired top cap ones with some smart wiring.
The key is to identify similarities and to reuse not used pins from a pinout to enable other type (in case of 2) you can put anode on pin 8 and also top cap).
Of course, you need to know a little bit how pinouts and adapters work and also to verify.
Golden rule: Never take as good what others advise and ALWAYS double check.
Similar things and tricks are also available for loctal adapters, basically with 2-3 types you can use anything. LOL
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