Output Transformer ClassA 3.5/5.0K 15W

Class A, 15w, 3.5K / 5.0K Output Transformer.  This is the same great sounding OT we use in our GU-50 Kits.

Why do you require a specific Class A transformer?  The vast majority (>98%) of output transformers made today for designed/built for Class AB circuits, which have a convenient pause between phases which removes the possibility of core saturation.  However Class A circuits operate at 100% duty cycle, so require a special wee gap installed in the core of the laminations, which eliminates the problem of core saturation.

3 1/8″t x 3 3/16″d x 2 5/8″w  3lb 5oz  Bolt Centres 2″ x 2-5/16″ m3 or m4

80t x 82d x 65w 1.5kg  Bolt Centres  51 x 58mm  m3 or m4

Primary:  White:  B+, Red 3k5, Yellow 5k0 (to be verified)*

Secondary:  Black:  Ground, Green 4 ohm, Blue 8 ohm

Note:  The manufacturer of these transformers is a wee bit sloppy with the varnish dip.  With varnish ending up on everything including the wires and bells.  So we replace the bells with brand new ones, the wires are fine with a bit of varnish on the jackets (and you can’t see them anyway).   This is a common issue with many transformers.

Caution!  Never sand or scrape transformer varnish off the metal laminations, this is what isolates the sections of the transformer and hold everything together!

*To verify the lower/higher impedance, simply measure the resistance across the White wire and Red / Yellow wires.  The lower resistance = 3k5 and the higher resistance = 5k0.  This is always good practice as sometimes manufactures will accidentally swap the wire colours.  Nothing will blow up if they’re installed in reverse, but you may lose some power (and nobody wants to give up power in a Class A Tube Amp!).