My first build from scratch...an Express

[M Fowler]

That is why I use Mojotone 3/8" long threaded pots but 1/8 faceplate is slightly too thick in my opinion and past experience.

Mark

[Tillydog]

I counter-bored the back of the faceplate to fit over the pot nuts. The pots can then be bolted tightly to the chassis and the faceplate placed over the top - The input jack, indicator and switches fasten through the faceplate and hold it in place.

YMMV.

[donzoid]

Thanks guys...good info for future builds. Darn good idea about counterboring I had not thought of that or I wouldn't have just spent an hour with my half-sheet sander on the backside of that plate. Mark I agree I would think they should even change the spec on our cabinet documents to 1/16th or 3/32" not 1/8". But that is a good workaround and I "had" thought in the midst of the process....I wonder if other pots (mfg's) have one more thread? . That's about all it would take.

Now that I've done it, I think a piece of veneer would have been faster and easier, but maybe harder to keep flat. Onward!

[donzoid]

What say ye on the jack? Should I just use a switchcraft or will this jack work being the isolated type?

[donzoid]

Just tried the presence pot, and its only grabbing half a thread...that ain't gonna hold. Counterboring, here I come.

[Tillydog]

What say ye on the jack? Should I just use a switchcraft or will this jack work being the isolated type?

I think you can get both with extended bushings (and pots for that matter), but I used an isolated jack with a short jumper from the ground on the jack to the chassis next to the jack - you could countersink the bolt for the ground tag into the front of the chassis, behind the faceplate, if you wanted to hide it.

[donzoid]

OK...I will tie the front star ground buss wire over to the jack because I wanted that type for the input (plus I have a few spares for my Marshalls lying about. Here is the faceplate after taking a 1.25" grinding ball as my counterbore. Worked out well. Faceplate will lie flat and that was much faster and easier than more flat sanding. Had a chance to get some standoffs in place last night and hope to get my octals mounted and start nailing down the boards next.

[RJ Guitars]

Wood faceplates are challenging for several reasons... if you do get the shank threads long enough then you still can't really crank down on them to make sure your grounds are all good and the pots don't roll. If you solder to the back of the pots to make a good ground then that has a couple negative aspects to it... potentially noisy ground loops included.

I've used several different kinds of potentiometers and found that the inexpensive ALPHA's were among the most reliable... but they do have a short shank. The shank is slightly longer on the 3/8" diameter ALPHA than it is on the 8mm, but still not enough thread there for a 1/8" faceplate. PEC's are awesome but not cheap! I've had a couple bad experiences with Bourns and I like CTS just fine but they are twice the price of ALPHA's...

I keep these extension nuts around... they cost about 3X what an Alpha pot does but they can be sized to crank down metal to metal to secure the pot without crushing the wood for the ultimate functional option when using a wooden faceplate.

For myself I remain more fond of metal faceplates but I understand the desire to make it look like an original Wreck.

[donzoid]

Yep RJ....those specialty nuts would do the trick alright...but in the end, I think the counterboring option works just fine and those Alpha's are torqued down good n tight as a German virgin, so they aren't going to spin. I've done plenty of metalwork in the past but this has to be the first time I've tried a wood component on an amp (this thin). Metal would have certainly been easier...but I never seem to take that route no matter what the material... I am one of those guys that has to get my hands on the work to really learn it so it's been good. Going on 3 am and my brains are getting mushy so I'm stopping but here are some shots of the progress. I hope to have the leads dressed and ready for measurements and a final sanity check/bulb limit test on Sunday.

[donzoid]

Didn't get as far as I had hoped...had to do a bunch of "prototype engineering" to get my choice of pilot light socket and power switch to work without coming dangerously close to the power board components. Never, ever again will I use teflon coated wire. What a wrestling match! My strippers work OK because they are pretty good but that whole thing of trying to wrestle them down (twisted) was a major pain. Next time I'll use solid core.

[RJ Guitars]

... Next time I'll use solid core.

You are growing in wisdom each day. If you haven't already tried it... go with the PVC coated solid core copper then you can also get to perfect your soldering technique. That coating melts off just about the time you are thinking that looks really nice.

Thanks for sharing the journey.

rj

[donzoid]

A bit more -- tone pots and a few valve leads.

[donzoid]

OK...I think I'm ready for voltage checks. Couple of questions.
Are the leads correct on the input jack as far as the resistor? Or should it be on the right side and active when the plug is inserted?

And am I correct in assuming that placing a resistor across the inside and outside legs of the adjustable bias pot (mounted on the back panel) are the correct way to reduce my 50K pot to 27?) The resistor is 47K. So it calculates and measures as that. Just want to have a "sanity check" before I put the bulb limiter and power to this and start measuring. I admit I have quintuple-checked everything, but I am nowhere near the folks on this forum.

Note that because I have not yet found a pair of 6v6 (which is what I intend to run in this for less wattage) in old-stock, I will start up with a pair of el34 (since I can rob a pair out of another amp on hand). So because of all the things I have read about this being completely beastly (not a bad thing) I went ahead and installed a LarMar "just in case" I want to trim it a bit. I also have an Airbrake so that will probably be the preferred way to reduce the "edge".

[Tillydog]

Can't comment on the rest, but you might want to double check your jack wiring - it looks wrong to me.

Shield should go to the sleeve connector (top in the photo) with a link across to ground out the tip with no plug inserted (where the 1M is now). The core of the shielded cable should go to the tip contact (looks correct). The 1M resistor should go between core and screen of the cable.

Double check these, because I'm not sure which side of your jack is which.

Also, you need a connection between the ground on the jack and the chassis (as it is an isolated jack socket).

You may want to disconnect the MV and wire it stock until you have confirmed that the amp is working OK.

[donzoid]

Thanks Tilly I suspected I had the jack "bass-ackward" and its hard to see but there is a ground wire from the sleeve to chassis-- because the jack is rotated slightly, its impossible to see in that pic. I will get that shield moved to the sleeve lug, and re-do the resistor and link. Thanks!

Here is the corrected jack: in the picture the left side opens when the plug is inserted.