Monday, December 09, 2013

Our temperate region was hit with an abnormally cold storm, derailing my plan to drive across town and use appropriate power tools to fabricate an enclosure for the reverb amplifier. I was actually toying with the idea to clamp a temporary table to my radial arm saw project (future instalment) when I came across an old Bach trumpet case I had salvaged from a pile of enclosures that were slated for a stop in a dumpster.

According to the reverb pan, this case will work out just fine.

Gutting it was not nuisance free.

The glued in monkey fur (remaining after I peeled the fabric backing away, which was a chore in itself) gave me ample opportunity to oil up my language.

Ultimately, once the fire hazard levels of fluff were removed the case continued to show promise. The area to the right where the shim block is will be filled with the B+ transformer I'm adding to the party.

Before I get that far, however, I want to address the incorrect capacitor I noticed the last time I posted, because the additional transformer is too large to mount to the chassis and performing work with a tethered chunk of iron is going to push the nuisance aspect a bit. Here I've pulled the 0.01 Black Cat and have eased a 0.1 Aerovox Duranite into the slot.

Access to the leg of the potentiometer necessitated the temporary displacement of the Domino cap, here everything is in position and ready for soldering.

Once the potentiometer assembly was buttoned back up it was time to address connection to plate leg of the tube socket, however, the longer package in the 0.1 cap put the B+ a little too close to the grounded screw for my comfort.

Tasteful application of brute force corrected the interference fit.

Nice round bend taking up the slack.

With the chassis sorted it was time to address the previously discovered deficiency in the higher voltage secondary of my installed transformer. I had toyed with the idea of putting a step up transformer across the 50 volt CT winding, but tests indicated that it was overburdening the 50 volt winding, so that plan was scuttled and this transformer was brought in, which provides roughly 200 volts DC once rectified, which is plenty for me.

I got to fill in the empty eyelet with a ground reference due to no center tap on the transformer.

With my car still snowed in (we reached -10F/-23C and the old moisture bearing door seals quite literally have frozen this car into a solid shell, though I am certain the aircooled motor would fire right up - if only I could get inside to operate the car) I decide to hand carve the enclosure.

Naturally, the larger knife I would normally reach for in this instance is currently TRAPPED INSIDE MY CAR, so I had a go with an old box knife...

...which resulted in many shavings.

I think in the end it will all be worth it though.


pearshapedhuman said...

Looks like it's almost there. Too bad the cute little black PT doesn't work. Those big blue caps look cool.

A schematic would be helpful in seeing how you combined the Fender with the Kalamazoo.

I hope it works great!

krivx said...

Good call on keeping away that grounded screw away from the high-voltage. With rigid structures like PCBs it's easy to find a reference with guidelines for how much clearance you should leave but when things are compliant enough to flex into touching I usually just get super-cautious.

crochambeau said...

Thanks Dan! Yeah, hinging on how the unit sounds & performs I may have to draw up a map of it. I think those transformers will be a good match for a +/-15 supply in preamps or compressors, so, all is not lost. They did seem a perfect match when I first measured it.

Regarding the screw; yeah, it wouldn't have been a problem if I wasn't using up screws that are much longer than needed. Everything seems really solid, but I may still slip some heat shrink around the shaft and lock that in with a nut. Cheap insurance.