AB165 OT wiring

General discussion area for tube amps.

Moderators: pompeiisneaks, Colossal

Post Reply
Smokebreak
Posts: 1391
Joined: Tue Dec 18, 2012 5:53 pm
Location: Texas

AB165 OT wiring

Post by Smokebreak »

I just want to make sure I'm doing this right.
I'm replacing the OT in a '65 Bassman(sheet says AA165 but circuit is AB165).

The reversed secondaries, to make the wacky NFB work, has totally thrown me for a loop. Reason being, owner wants me to wire 1 speaker jack as 8ohm, and the ext. as 4 ohm.
I've already installed non-shorting jacks. I'm using MC 40-18009. So I was going to wire the black common wire to the tip, and jumper over to the tip of the other jack. So for the 4 and 8ohm leads, I was going to wire one to the sleeve of one jack, and one to the sleeve of the other.
This would keep with the original "backwards" wiring. However, since the sleeves have continuity through the chassis, it's like the 4 and 8 taps are connected.
This is blowing my mind a little bit. But, since the all the leads' duties are reversed, this should be fine, correct?
User avatar
martin manning
Posts: 14308
Joined: Sun Jul 06, 2008 12:43 am
Location: 39°06' N 84°30' W

Re: AB165 OT wiring

Post by martin manning »

Use the common on the secondary as intended, ground it, and use separate jacks for the 4 and 8 ohm taps. Now all you have to do is flip the primary leads.
Smokebreak
Posts: 1391
Joined: Tue Dec 18, 2012 5:53 pm
Location: Texas

Re: AB165 OT wiring

Post by Smokebreak »

Ok thanks Martin, and the NFB can come off of the 4ohm tap now instead of the common? I'll need to move that.

Sidenote: one of the screen resistors wasn't soldered in. Looks like it never was. It was barely hanging on, too. Owner reported zero problems.

edit: I meant to ask if the NFB stays on the tip, as now the 4ohm tap is there.
User avatar
martin manning
Posts: 14308
Joined: Sun Jul 06, 2008 12:43 am
Location: 39°06' N 84°30' W

Re: AB165 OT wiring

Post by martin manning »

Smokebreak wrote:edit: I meant to ask if the NFB stays on the tip, as now the 4ohm tap is there.
Yes, correct, if you want the same level of NFB. You have an option now with the 8-ohm tap too.
Smokebreak
Posts: 1391
Joined: Tue Dec 18, 2012 5:53 pm
Location: Texas

Re: AB165 OT wiring

Post by Smokebreak »

Thanks again Martin, it all worked out.
Post Reply