Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: heymymy on November 28, 2011, 09:25:59 pm
-
Hey, I've done a couple of builds and mods, etc (mainly JTM45 and 5F6-A type) but I picked up Vox's new AC30HW which is GREAT! and it's actually hardwired on a turret board. My question is I want to swap out the OT for a MM but I'm not really sure how to do it.
I've done OT swaps but that was always with detailed instructions or just copying a layout.
So they worked buy luck alone. I understand the basics on tube amps and how they work, but I really think it's time I found out what goes where and why. So If anybody could help me out with what each of the OT wires are and what they go to, I'd really appreciate it.
Here's what I researched already, let me know if I got it right.
8 & 16 Ohm Taps - go to the selector switch for the amp.
Common Wire - goes to ground?
Center Tap - goes to Cap Can B+
Primary Wires - go to the anode of each power tube. (pin 7 on El84.)
What else?
-
What MM transformer will you be using? You covered all the typical wires for a push-pull pentode/beam power tube stage. Unless your transformer has wires for screen taps, there shouldn't be anything else to consider.
-
If you tell MM exactly what you want the OT for they will most likely provide an OT with the same color leads. You also get a schematic of the OT. The swap is "color by numbers" easy.
-
Hey, it's the MM VXO-30W, I emailed them and this is the one they suggested for the '59-60 type box sound. I also picked up the choke too.
Does the Common Wire go to ground? I know on a marshall the common goes to the speaker input jack then the Ohm taps go to the switch, but looking inside this AC30 it looks like they've grounded the Common wire to the chassis from the OT and the Primary Wires are going to the little ohm switch with a short jumper wire to the speaker input jack.
Thanks for the help, I'm trying to go from "I can do it, to I know why it works."