Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Lomo on October 16, 2016, 10:34:23 am

Title: Speaker Touching Transformer
Post by: Lomo on October 16, 2016, 10:34:23 am: Hello Everyone. I'm new to this forum. I recently purchased a Vox AC4C1. I thought about swapping speakers. So I install a Celestion Vintage 30 that I had laying around. But the speaker magnet touches the transformer. I did not turn it on. What problems (or not) can expect? Thanks
Title: Re: Speaker Touching Transformer
Post by: shooter on October 16, 2016, 11:08:52 am: Quote
What problems (or not) can expect?
there might be mechanical noise, if it's a gigging amp, all the in and out, banging around probably won't be good over time. play it and see. if you like the speaker, maybe elongate the screw holes enough to move the speaker, rubber type shim, etc.
Title: Re: Speaker Touching Transformer
Post by: eleventeen on October 16, 2016, 07:50:36 pm: There are a few things you can do, depending upon exactly how your amp & cabinet are built. You're just gonna have to consider these and ponder how much work you're ready to do.
I am assuming the speaker mounts from the inside of the amp. You could change to front-mounting it. You may have to destroy your baffle board and remake it.

If the baffle board screws into the rest of the cab, you could get some sort of 1/8-1/4" spacers and move the baffle board forward a bit. Of all the possibilities, that would probably be the easiest. Of course if the Baffle board is glued in..... then no go.

The second easiest thing would be if your grill cloth is on a lightweight frame that velcros to the front of the amp. Then you enlarge the speaker hole and change to front mount, most likely can use the grill cloth frame as it. Fairly painless.

Elongating the speaker mounting holes and/or moving the screws, as Shooter suggested, is a possibility. There will be plenty of opportunities to trash the grille cloth in this operation unless you are very careful.

Worst case, the current baffle board is glued in and you have to hack out the baffle board, leave stubs along the sides, and make a new one with the speaker moved off-axis to a different location. That will probably cause problems with the new speaker mounted either too far forward or towards the rear. AND force you to make a new baffle board. Not pretty.
Title: Re: Speaker Touching Transformer
Post by: kagliostro on October 17, 2016, 02:06:25 am: Seems that the grill cloth is stapled to the baffle and the baffle screwed to the cabinet

(http://i.imgur.com/kvN1hZC.jpg)

in the front there is a very small space that you can take advantage of, unscrew the baffle and between it and the cabinet put a thin material

(http://i.imgur.com/xjhJt7D.jpg)

Franco
Title: Re: Speaker Touching Transformer
Post by: tubeswell on October 17, 2016, 02:19:58 am: I would be concerned myself if there was any pressure contact between the two items OR any vibration of the OT or speaker.
Title: Re: Speaker Touching Transformer
Post by: JB on October 17, 2016, 03:16:28 am: I'd pull the chassis first and see if the transformer can be moved a little. Worst case drilling a couple of holes and remounting. Might even get away with enlarging one or both of the holes a little to pull it out of contact.
Title: Re: Speaker Touching Transformer
Post by: kagliostro on October 17, 2016, 03:35:07 am: I think that is difficult to do that, look to the image, there are the switch and the lamp

and also the bolt is positioned in a way that I think it is near the border of the chassis

(http://i.imgur.com/kZzE5uV.jpg)

(http://i.imgur.com/ihM9CDo.jpg)

Franco
Title: Re: Speaker Touching Transformer
Post by: JB on October 17, 2016, 04:54:18 am: Quote from: kagliostro on October 17, 2016, 03:35:07 am
I think that is difficult to do that, look to the image, there are the switch and the lamp

and also the bolt is positioned in a way that I think it is near the border of the chassis
Franco

That's the power transformer next to the switch/lamp. Looks like plenty of space to move the output transformer further away from that speaker jack pcb. 10, 20 mm would do it. Easy quick fix!
Title: Re: Speaker Touching Transformer
Post by: kagliostro on October 17, 2016, 09:46:59 am: Quote
Looks like plenty of space to move the output transformer further away from that speaker jack pcb

You are right, that must be the OT not the PT and that is very easy to fix

K
Title: Re: Speaker Touching Transformer
Post by: eleventeen on October 17, 2016, 10:33:01 am: Yup, moving the OT would be a bit easier than putting spacers under the baffle board. Not as reversible, though. Before making the decision I would be very careful to be certain that the speaker magnet does not short anything on the little PC board. Anyway...you've gotten some ideas.
Title: Re: Speaker Touching Transformer
Post by: JB on October 17, 2016, 11:38:19 am: Looks like the speaker jack PCB can stay put, it's just the transformer that needs to shift a fraction.

Don't put it right down the end near the preamp - you might pick up some hum. If you're concerned about that then unbolt it and carefully move it a little with the amp powered/speaker connected and listen for any hum increase. Usual live working safety rules apply here.
Title: Re: Speaker Touching Transformer
Post by: kagliostro on October 17, 2016, 12:00:46 pm: If necessary (I don't think it will be), you can shape as an L a metal sheet to use it as shield (alluminium is better)

and fix it with two holes in correspondance of the OT mount holes

(do it of course on the short part of the L shield)

Franco
Title: Re: Speaker Touching Transformer
Post by: Lomo on October 17, 2016, 01:42:53 pm: Outstanding!!! I think I will move the tranformer a tad. Thanks everyone!!!!!