Mainline Build Questions

[adydula]

Hello,

Got my kit yesterday and am starting the install of the mechanical parts.

I am missing one of the #6 smaller fiber shoulder washers used or the OT3 transformers.

It looks like these fiber shoulder washers center the mounting screws so they dont touch the sides of the main panel and
thusly isolate the transformers chasis from the mounting plate?

On the one OT3 I have mounted the resistance between the transformer mounting case is infinite.

So is this very important that these xfmrs are indeed mechanically and electrically isolated from the main panel??

Thanks
Alex

[adydula]

OK second "dumb" question....:>)

When mounting the volume switches on the small aluminum plate.

Your instructed to remove the 4 components, then set up the stop washers for the 5 clicks and 6 positions.
No problem here.

Then when you mount the switches, there is no mention of using the lock washer? Is this intended or is it not used?

Thanks
Alex

[Paul Birkeland]

If you're missing a #6 shoulder washer, then yes, I would ask for a replacement to be mailed.  The transformers are all isolated from the chassis but provided dedicated connections to safety ground. 

On the attenuator switches, the lock washer should go right under the nut, but it's not the end of the world if you don't use it.

[adydula]

Again thanks...I used them....please dont take my anal questions the wrong way..I was a software, tech manual QC guy!! lol...

Soldering the boards now and painted the Bell housing ...looks great.
Alex

[Paul Birkeland]

When you get anal and take your time, your build will reflect that (in a positive way).

[adydula]

Ok heres another thing I noticed:

In the instructions is calls for 3W and 2W 100k resistors:

100KΩ 3W resistor (brown, black, yellow, gold) into the R2 position on the A side

100KΩ 2W resistor (brown, black, yellow, gold) into the R2 position on the B side

In the schematic I see 100K 5 watts 5% in the dual shunt regulators??

Alex

[Paul Birkeland]

I believe when the schematic was drawn, we had a 100K/5W part in the inventory.  The resistor dissipates about 0.75W, so a 3W part was substituted in its place to make for a cleaner build.  The 5% note in the schematic is PJ's way of saying that the tolerance isn't super critical.

[adydula]

Is the reason the transformers are mounted with insulatiing washers for safety only? or is there any reason electrically? is ground loops or grounding issues circuit wise?

Understand the safety ground...

Alex

[Paul Birkeland]

Isolating the transformers from the chassis reduces magnetically induced currents in the chassis plate itself, which helps provide a lower noise floor.

[adydula]

Thanks for that information, quite interesting.

Well, I got all four boards populated and soldered up, cleaned with alcohol and a acid tin brush to get the flux residue off the bottom side of the boards. Just waiting on the 49.9 ohn resistors to complete.

Everything is mounted on the main panel except one of the OT3 transformers (need the fiber shoulder washers) and the Primary power transformer....waiting for my bell housing paint job to dry....:>)

Will stop and recheck all parts install for correctness and then start on the wiring stuff.

When you open the box at first I thought gee there's not really much too this amp! Then when you start working on it you realize this is more than a one day project !! :>)

Really enjoying the build so far...

Alex

[adydula]

Ok. I was mounting the power transformer and noticed I am missing (2) of the star washers...so the next dumb question is:

Can I use plain old lock washers here??

Alex

[adydula]

Ok. I went over to the Lowes hardware store and bought some star washers, rather than wait for the ones in the mail...np.

I also sovled the issue of the missing fiber shoulder washer I had some fiber washers in my tool "bag" and made one up...

I noticed that when I tightned down the screw and leasure the case of the OT3 to the main panel it was shorted out...

The OT3 transformer (only one) had its outside metal casing crimped on the bottom of the laminations, well on one it wasnt crimped nice a flat and
even with the fiber washers it was scraping the main panel...I carefully pressed it down and voila its not shorting to the panel.

So I have all the mech stuff done and but for the 49.8 ohm resistors the boards are done as well...

So on to the wiring and hope the resistors arrive soon,,,

Alex

Tww coats of Tung Oil so far...

[adydula]

OK,

Power supply test loks good!

6.3VAC and 390VDC.

I was mounting the power supply board and discovered I was missing (4) of the 8/32 x 3/8 screws....had enough washers nut missing 4 of these only had one in the kit package?

Ran ut to Lowes again and found out they mostly only have down to 1/2" 8/32...but had some 3/8" stainless with allen cap....got these and they worked just fine.

Ok continuing on with the wiring....

Alex

[adydula]

Input Wiring...

[adydula]

Got thru the stepped attenuators and some more of the wiring.....done for today the lights gone!! lol.