VOX - AC30 Output Transformer - Wiring Clarification

[RJ Guitars]

Hello Forum,

I am building a Trainwreck Rocket amp using all VOX transformers. If you are familiar with the VOX output wiring from the transformer to the speakers you might agree that it's a bit unconventional.... lots of terminals and three output jacks?

The transformer input seems clear enough. but it's not so clear about everything they had in mind on the output wiring - see attached drawing.

What I believe:

A) Black goes to ground.
B) Blue to the 16 ohm tap
C) Green is an 8 ohm tap

My main question is - do I simply ignore the 16 Ohm tap, leaving it open when i want the single 8 ohm tap? Leaving half of the transformer windings unused seems like it is bad since there isn't some sort of load on it... but maybe you can enlighten me.

I have a 16 Ohm cabinet so it works out easy enough, I'm just curious what all they had planned and want to have the 8 ohm option in the event I use a different speaker cabinet. The wiring drawing I have is fuzzy and I can't follow the signal path with any confidence.

Thanks for any insight you guys can provide on this.

rj

[Phil_S]

If you have one jack for the 8z tap and another jack for the 16z tap, you plug into one or the other, the appropriate load, 8 to 8, or 16 to 16. You need a load on the power tubes. The OT will be fine.

If you plug into both at the same time, it is a parallel connection and the standard rule for resistors in parallel applies. The speaker cabinets will be half of what they normally are; that is, the 16z will be worth 8z, so you'd need a 32z cab for the 16z jack, and a 16z cab for the 8z jack. Don't have a 32 Ohm cab? Rewire that 2*12 -8 Ohm load (16's in parallel) to series wiring. Better yet, put a switch on it.

[RJ Guitars]

Thanks for the reply Phil.... So I am curious what everyone thinks about using a scheme that allows me to get 16 ohms or 8 ohms the old fashioned straight forward way, but also allows me to get a 2nd 8 ohm tap in the event I have two 8 ohm cabinets. In this case I can legitimately run 4 ohms, an option I would like to have.

Any technical reason I can't do this?

I have reversed the leads going into the J3 jack so that it stays in phase with J2.

I think this might be something like VOX was doing on their original. It had a single 16 Ohm Jack and a pair of 8 ohm jacks also. However, I am not able to follow their work well enough to see how or if they run a ground lead to those jacks.

rj