Z-mounting a stand-up

[Matt T.]

I have a PT that originally was made to be a stand-up. I'm going to try and mount it laydown but I've never done the conversion. I assume I can just pop off the end bells (which I've already done) and mount it and away I go? But I've also seen these laydown mounting brackets, do I need one? Is it just for strength...because if it is I could probably get away with a couple of flat bars with holes drilled in them. The chassis is Aluminum but it's a bit thicker than usual. Would washers be enough?

Second question is about the copper band around the PT. It looks like it's just wrapped around the PT with nothing really holding it on other than it's stiffness. With the end bells on that was not a problem but since I'm taking both end bells off (the bottom end bell is the wrong color and it's a stand-up end bell with mounting feet...so I figure no end bell looks better than that), that copper band seems loose. Should I secure it somehow and if so...how?

Thanks for any help.

[bob p]

well, i'm no transformer engineer, but i would prefer to mount the PT with the end bells in place if at all possible. in addition to holding the copper strap in place, the end bells also provide electromagnetic shielding to diminish the effects of the PT's electromagnetic field on surrounding structures. you might notice more 60 Hz hum with the endbells taken off.

you may also notice that the noise can be worse with the PT laying down, with its laminations in the same plane as the chassis. that arrangement can couple hum into the chassis. all things considered, i'd prefer to mount the PT standing up, with the endbells on.

[Matt T.]

Well that's not good news. The old PT is/was perfectly functional but it's a Hammond 272JX and it puts off a massive magnetic field and you can't stand within 6 feet of the amp. I tried two Hammonds when I built the amp and both behaved the same...you can even hear/feel the vibration in the chassis when it's turned on (many people have complained about this with these exact PTs). The voltages were wrong too due to the 115vac rated primary but I had dealt with that...the thing that put me over the top for swapping it out was that massive magnetic field. I hope it's not more noisy...chassis is Aluminum.

[MWJB]

I've mounted a Hammond 374BX PT laydown style (drops right in to a Fender Twin chassis hole) with no issues whatsoever.

Kept the primary side end bell on (the colour didn't bother me, I'm not sure who would be looking under my amp anyway), stand up bracket didn't foul anything, ran primaries through a grommet in the chassis, no endbell on secondaries side.

Don't the mounting bolts keep the tranny integrity?

Watch the routing of your heater wires, if these cross back over the PT they can cause hum & vibration.

I have also seen PTs with a loose-ish copper band. Again, in my case, no untoward symptoms.

[Matt T.]

Well I finished it up this weekend. I mounted it with no end bells and with the copper band still on...I just used some washers for strength. Bob was right about it transmitting vibration to the chassis...it vibrates as badly or maybe even a tiny bit worse than before but the magnetic field surrounding the PT seems to be much less. I can actually stand within reasonable distance of the amp when it's cranked.

The voltages are lower (402 B+) so I used a 10K resistor in the power supply between the screens/PI instead of 20K to get the preamp voltages up a bit (it's a Marshall smallbox clone). The amp sounds better than ever...it's not as loud (which isn't a bad thing!)...and it's extremely quiet regarding noise/hum.

(the colour didn't bother me, I'm not sure who would be looking under my amp anyway),

lol...for whatever reason the fact that the amp looked bad (mainly the wiring...not the end bell color) really made me want to gut it and redo the whole thing (which I did...new custom G10 boards and everything). I don't build that many amps so I wanted this to look nice as well as sound nice. At this point it's something I can be proud of...not so much before.