Champ OT Question - TUT3

[johnboy]

Hi All;

Long time lurker, first time poster.....

I'm working on a Champ head for an 8 ohm cabinet based on the one presented in TUT3.

I'm using a Hammond 125C OT - only half of it, with the centre tap tied to B+. KOC notes that when doing this the impedence the tube sees is 4 times what's shown on the hook up chart.

So - to get the normal 5000-7500 ohms at the 6V6 when using the full OT, should I hook up the speaker to the lugs that provide around 22000 ohms for just half of it?

Does that make any sense at all? Might be a stupid question - I just can't quite wrap my head around it....

Thanks,

johnboy

[Dave H]

Using the full primary (brown-blue) it says you can have either a 2.5k or 4k impedance when using the listed secondary impedances. To have a 5k or 8k primarary impedance you'll have to use a speaker of twice the listed impedance. i.e. use a 16 ohm speaker on the 6/8 ohm tap or an 8 ohm speaker on the 3.2/4 ohm tap.

Dave H.

[mooreamps]

that's not the only thing. My understanding of push/pull output transformers, might have equal bias currents on both sides of the primary, as I have read in one of keven's tut's ; or you have problems with heat.

-g