Transformer / PS board bolt interference

[Ron Worley]

I'm attempting to layout the holes in my Alllynmey chassis, and I think that I have an interference problem with the heads on two of the PS board standoff bolts (on the tranny side of the chassis).

The one under the PT might clear due to the cutout in the tranny base, but the bolt under the OT is right under the flat base of the tranny. See the attached Word document with the blot positions circled in red- it would be the opposite bolt on the other side of the circled standoff position.

Perhaps I am missing something very obvious here, can anyone help??

Thanks in advance,

Ron

[Ron Worley]

This is the initial drill pattern template for the Express Chassis I developed, which lead me to question the interference of the one or two PS board standoff bolt with the trannnies....

[Ron Worley]

BTW, any and all corrections on dimensions are appreciated... this was tough to do trying to scale things from the Francesca pics...

Ron

[UR12]

You need to use a counter sunk head screw and carefully drill out the holes under the trannys to except the counter sunk screes so their heads end up flat with the top of the chassis

[Ron Worley]

Thanks Dana... that makes a ton o f sense. Any comments on the dimensions for accuracy?

Ron

[philmanatee]

I've got a countersink bit and I didn't even think to use it when I built my express, I just threw some washers under the transformer. :oops:It worked fine, I've since used the countersink bit with great results. Just go slow and check the depth with the screw so you don't take out to much metal. Phil

[Ron Worley]

It's funny... rather like an onion... as you peal back the layers you discover so many minor yet important details as to how Ken built these amps.. I guess that's part of the fascination I have with the Wreck...

Ron

[geetarpicker]

In a real Express of few of the standoff screws aren't even really attached by a screw at all, at least in mine. The ones that go right under the transformer are simply sitting on stand offs that are screwed to the board, but actually just glued with a dab of silicone to the chassis. I did my two clones the same way. You simply attach all the standoffs to the board and put a little silicone on the ones that float as you mount the others with screws. I guess a counter sink is nicer, but in my original none of the siliconed standoffs have ever come loose. The 3 screws down the center go all the way though, the one near the ground tab at the back is screwed, and the other 3 are siliconed.

Needless detail I guess.

[Ron Worley]

Glen-

I wouldn't say needless at all- it just depends on you level of detail (or anal behavior I suppose). It doesn't seem to have been addressed before, but I will search the board to make sure. Probably should have first.

It seems to me with the sensitivity of this amp, having only about half of the PS board securely mounted is not really such a good idea over the long run. But what do I know?

Thanks for the insights as always!

Ron

[Noel Grassy]

Ron, IMO that board mounted with just 2 standoffs diagonally opposed would seem quite stout since nothing changes the pressure applied on this surface. The silicone/"glue" dabs should be ideal as they could absorb some deflection should it arise. YMMV

[Ron Worley]

It did occur to me that the silicone might actually act as a "shock absorber" as you mention.....

I bought some flat head #6 stainless just in case I want to mechanically mount them all.

Ron

[drhulsey]

... an interference problem with the heads on two of the PS board standoff bolts...

The aluminum on Allyn's chassis was thick, so I just threaded the hole to accept the mounting bolts. The length of the bolt was adjusted to keep it flush. I wouldn't want to do them ALL that way, but with all the other bolts and nuts in place, the PS board is plenty stable.

[UR12]

It's funny... rather like an onion... as you peal back the layers you discover so many minor yet important details as to how Ken built these amps.. I guess that's part of the fascination I have with the Wreck...

Ron

Two of the bolts holding in the power tranny that are nearest to the "Stack-o-caps" need to be reversed with their heads on the inside the chassis in order to have room for the caps between the boards.

[Ron Worley]

I did notice that on the Francesca pics (attached)!

[Ron Worley]

Here's the latest drill pattern with some more adjustments on dimensions (moved the Preamp board closer to the pots)

Ron