Amp dudes amp question:

[MDV]

I found two =C= EL34s. The valve fairy put them in my valve drawer and didnt tell me.

I will put them in my JVM410H

Its 100W, obviously.

Do I run it out of the same impedance as normal, or run it out of half impedence (4 ohm in this case)?

[Frank]

Impedance ratios are FUN!

Ballpark figures, let's assume it's 5k ohms R_a-a with 4 output tubes to 4, 8, 16 ohms. Popping two tubes means you need to reflect 10k ohms to the primary because you've removed half the parallel resistance. That means your 4 ohm tap (5000 to 4 impedance ratio) with 8 ohms across if reflects 10k to the primary of the OT.

tl;dr - yes. Enjoy your Winged =C= growl.

EDIT: That's yes to half impedance by the way. Use the 4 ohm tap for an 8 ohm speaker.

[MDV]

Thanks :)

TS;WM if anything.


Not afraid of technical exposition, dont understand a couple of terms in there, could do with a glossary, but i get the jist; for the valves to see the same load when running half your power amp you need half the impedence. Gotcha.

[Frank]

Let's try an easy version then ...

* OT matches the high impedance of the valves to the low impedance of the speaker
* If four tubes need to work into a 5000 ohm load then two tubes will need to work into a 10,000 ohm load
* If your OT ratio matches 5000 to 4 ohms (on the 4 tap) then it will match 10,000 to 8 ohms on that tap