Let's Get Technical > All PREAMP Tech Tips & Support

Preamp Case/Chasis Screws

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rnolan:
As I said on another thread, the only ADA preamp I have with all its screws is my original MP2 bought new, I have only had the top off this unit a few times (EPROM upgrade, 3 x tube changes (1. SPAX7s not optimal); 2. NS LP Mullard 12AX7; 3. new NS LP Mullards)).  I even went as far as always putting the screws back in their original holes (call me pedantic but don't call me late for dinner LoL).  And even with all that care taken some wont tighten down properly anymore.

All my other units (3 x MP2, 2 x MB1 & 2 x MP1) have screws either missing or wont tighten (partially stripped).

With the MP2, the 3 screws that mount the lid to the heat sink (which is aluminum) strip and end up loose, and sometimes fall out and/or are hard to remove (which you have to, to take the top off). I can sort of live with "some" of the other screws being missing/loose but it's important that the heat sink mounts solidly to the top to dissipate heat (which MP2s make quite a bit of).

So I'm sure I'm not alone in this, what are good solutions fellow ADAers ?
Very slightly larger screws ? possibly the difference between metric and imperial can help here ?? as in the closest metric (almost) equivalent is just a little larger  :dunno: .
Some sort of "lock tight"
I've tried thread tape (on the MP2 heat sink screws), it's a pain to do and doesn't work

Soloist:
My Mp1 was missing a few screws and the holes were striped. I used a slightly larger self tapping sheet metal screws. Worked like a charm! Don't forget to paint them black first like I did. :nono:

MarshallJMP:
The original screw are 4-40 x 1/4 (if I remember correctly) which is around 2.8mm so the next in line in metric would be an M3 screw. If I have stripped threads I first use an M3 tap (be careful with the small metal pieces that could fall) and put in M3 screws. Works great.

Iperfungus:
This issue with screws seems to be very common with ADA stuff...:facepalm:

I remember many screws of my old V1.38 had this problem.

Now my main MP-1 has 100% perfect, tight screws.
But the 2nd one with issues I recently bought have just of couple of screws that work fine...

MarshallJMP:
I actually only use 2 screws to secure the top lit. It's easier to change tubes if needed.

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