Trainwreck Express build, PT hum on and off standby

Alexo · Post by **Alexo** » Wed Feb 09, 2011 5:07 am

LarryLarry wrote:Well, I found no difference moving a metal plate between the transformers or any other internal location regarding the hum, so for now I'll live with it.

What kind of material was the shield? Got any aluminum?

LarryLarry · Post by **LarryLarry** » Wed Feb 09, 2011 5:12 am

I used some thick copper foil, but I did use aluminum on the other amp I built that had some hum. I'm sure I have some donor aluminum organ or stereo chassis somewhere...

LarryLarry · Post by **LarryLarry** » Wed Feb 09, 2011 5:24 am

More or less done for now. Will check it out at band practice tomorrow night.

I need to find some hardwood to build a proper front panel for the head, and eventually I'll either replace the PT or attempt to re-orient it to get rid of the hum...

Alexo · Post by **Alexo** » Wed Feb 09, 2011 3:37 pm

Have fun, I'm sure the hum won't bother when you're tearin' it up at practice!

LarryLarry · Post by **LarryLarry** » Thu Feb 10, 2011 6:23 pm

Ok, the amp sounded totally awesome with a band, I'm happy! I ran it with 6V6s biased at 23ma with 415vdc on the plates. The 2x12 cabinet has an older greenback that I blew many years ago and had Ted Weber recone with a 50-watt voice coil, and an early 90's Celestion Mesa MC-90.

The PT hum was not an issue at all at practice but it is when I'm in my studio. So, I may try to reorient it...

LarryLarry · Post by **LarryLarry** » Fri Feb 11, 2011 3:44 am

Well, I temporarily disconnected the PT from the L brackets and angled it in a lay-down orientation and -all- the hum went away, quiet as a mouse.

So, I'm thinking of stand-offs on the 4 corners to put it in the lay down position, but above the chassis. The depth of the side of the bell that would have to go into the chassis is almost 2 inches - the total depth of the chassis, so that's a no go.

I'll be hitting Home Depot tomorrow to see if I can come up with anything safe, sturdy and something MacGyver would be ok with...

rdjones · Post by **rdjones** » Fri Feb 11, 2011 5:54 am

LarryLarry wrote:I used some thick copper foil, but I did use aluminum on the other amp I built that had some hum. I'm sure I have some donor aluminum organ or stereo chassis somewhere...

I don't think either copper or aluminum will have much effect,
you need something with the correct magnetic properties. <steel>

rd

LarryLarry · Post by **LarryLarry** » Sun Feb 13, 2011 5:47 am

Ok, well I didn't give up my quest to conquer the beast-of-hum and I'm glad to report mission accomplished.

All that talk about 90 degree orientation for PT/OT just left the building for what I'm working with.

Had to re-orient the PT to a lay down position, but it is so big I didn't have room to carve the hole for the entire bell. So I constructed some standing 'legs' made of nuts, couplers and of course duct tape. Good enough for Apollo X111!

Also had to offset the OT by a few degrees to kiss the final bit-o-hum goodbye.

I now have to bend down and put my ear to the speaker cabinet to tell if it's really turned on!

Looks like I've got a chassis that is too holey and transformers that are obviosly not PC - so I've got an amp only a mother could love!

Youz can call me mamma...

M Fowler · Post by **M Fowler** » Sun Feb 13, 2011 4:39 pm

Makes me wonder if that PT has a problem if this was the only way to solve the noise?

Once the chassis is covered by the head shell only you will know what lurks behind the wood

Mark

martin manning · Post by **martin manning** » Sun Feb 13, 2011 5:14 pm

LarryLarry wrote:All that talk about 90 degree orientation for PT/OT just left the building for what I'm working with.

But your PT and OT are oriented 90 degrees apart... well, 85 degrees, anyway.

LarryLarry · Post by **LarryLarry** » Sun Feb 13, 2011 5:51 pm

Yeah, I guess it's about 85 deg now. But if I move the OT in any direction clockwise or counter clockwise I get some hum. Mind you, the hum is only about 1/4 of what it was when I had the PT standing up, but now it's so quiet I find myself putting my ear down to the speakers to see if it's really turned on.

I'll be glad when I finish the front panels so I can hide 'the monster'!

LarryLarry · Post by **LarryLarry** » Mon Feb 14, 2011 6:36 am

Very close to being done!

LarryLarry · Post by **LarryLarry** » Mon Feb 14, 2011 8:03 pm

Added a last clear coat and some piping between the front panels. I'm calling it done!

surfsup · Post by **surfsup** » Mon Feb 14, 2011 8:07 pm

That's awesome! So what did you do remove one threaded post at a time on the bell covers and replace with a longer one with a spacer?

EDIT, weird the pics didn't load first time. I see them now.

LarryLarry · Post by **LarryLarry** » Mon Feb 14, 2011 8:12 pm

Thanks! I could only get 2 of the 4 screws out (1962 Foster PT) so I replace those with longer screws. Then I used coupler nuts along with some other nuts and a couple spacers (to match the 2 pairs of screw lengths), then I wrapped them each in duct tape to slightly de-uglify it

Also several lock washers in the mix for counter pressure and stability.

Tube Amp Archive

Trainwreck Express build, PT hum on and off standby

Re: no go on the shield

aluminum

Done for now

Re: Trainwreck Express build, PT hum on and off standby

sounded awesome!

it wants to lay down

Re: aluminum

what hum?

Re: Trainwreck Express build, PT hum on and off standby

Re: what hum?

85

very close

done

Re: Trainwreck Express build, PT hum on and off standby

PT mods