Mellow Yellow Bass Kit Build

What?  Another bass kit?  Had I lost my mind?

I hadn't planned on building another bass kit, honest.  (See my experiences with my previous kit here:  http://k6jca.blogspot.com/2013/09/building-bass-guitar-kit-part-1.html).  But while searching ebay last year, I came upon this kit:

A classic body look similar to a '51 bass (which I've always been partial to).  And, most importantly, there was a lefty version, too!

And it had a humbucker?

OK, I was intrigued.  I'd never tried a lefty humbucker bass; this might be my chance.  But what was with the weird (and amazingly ugly) headstock shape?  Looked like the headstock was trying to morph into a pumpjack.

Well, I figured I could probably fix that with a saw.  So, what the heck.  I ordered one.

It's here!

The box arrived...

OK, first things first, I took inventory.  Everything was there this time.  But the control plate was made of plastic (the same material as the pickguard -- guess they didn't have a lefty version in metal).  And again, the nut was a righty version (the built-in slope is in the wrong direction).

But none of these were show stoppers.  So on to the next step:  completely assemble and check that it sounded halfway decent before investing time and money to reshape the headstock and paint the body.

First, mounting holes needed to be drilled for the following:

• Pickguard
• Control Plate
• Jack plate
• Pickups
• Bridge
• Strap Buttons
• Tuner Screws
• String Retainer

I also drilled out the 4 holes in the body for the neck screws -- they were too small, and the neck screws would have bit into the body wood as they were being screwed in, which was something I didn't want.  The screws should pass through the body unimpeded and only bite into the neck wood.  Otherwise, I would run the risk of not being able to adequately tighten the neck to the body.

As I assembled the bass, I discovered a few more issues.  Some of my own making, some not.

First, my mistakes:

1.  I initially mounted the bridge a little to close to the neck pocket, so that when I tried to setup the bass, I discovered that the saddles were getting very close to the back of the bridge.  Redrilled five holes closer to the end of the bass and filled the first five holes with bondo (next time will use dowels):

2.  Made the holes for the tuner screws slightly too small (I think).  One of the screws broke when I was screwing it in to the headstock: 

Had to dig a bit into the wood so that I could grab the broken-off end with a pair of pliers and unscrew it.

And the manufacturer's issues:

1.  Right-handed nut, not a lefty (slots sloped the wrong way).  I first tried filing the slots to give them the proper slope (towards the headstock, not the bridge), but this put the strings so low that they would rattle on the frets between the nut and the fret I was fretting when I plucked a string.  So I found another nut in my spares box and installed it.  (In hindsight, I probably could have just added a shim below the original nut after I'd filed it.)

2.  The pickup route was just a bit too small for the pickup's mounting ears!  Fixed with files/sandpaper applied to sides of the pickup cavity.

3.  Neck cross-section not symmetric.  Looks more like an airplane wing.  Can't fix it, but it doesn't seem to be a problem.  Just sloppy manufacturing and poor quality control.

 4.  One end of the third fret is a bit short:

Not going to fix that,

5.  Sharp fret ends:  file them down.

6.  Neck plate not squared to body (i.e. body holes and pocket not squared to body):  File the body holes for the neck bolts so that they're a bit wider, to give some room to square up the neck and sand the sides of the neck pocket to give me enough range of movement.

7.  E-string tuner slightly offset so that when only the E-string is installed, it wants to slide the nut sideways.  Not a big deal, but still...

On the plus side, the frets seem level this time.

Assembly is done, how does it sound?

Plug it in and turn on the amp.  Wow!  Lot's of hum!!!

Wiring looks OK -- let's see if shielding helps.

First, let's pick the low-hanging fruit and shield the control cavity and the plastic control plate with 1/2" copper tape from the junkbox:

Hmmm...still lots of hum.  Must be capacitive-coupling to the pickups.  Let's shield the heck out of them:

First, wrap each of the coils in copper tape:

Then add tape to the top of the pickup:

Note that these top pieces of copper tape are soldered to the copper tape on the sides of the coils, so that there isn't any solder on top of the pickup that might prevent the pickup cover from going all the way onto the pickup body.

 And finally, add copper tape to the back of the pickup:

This may be going a bit overboard, but I figured better to do as much shielding as I could, all at once, rather than piecemeal.

All pieces of copper are connected together with solder (spot-tacking is fine), and then attached to the pickup ground at one spot.

Reinstall the pickup and test:  no more hum!!!

[Sidebar on hum:  I believe that humbuckers get their name from preventing magnetic-field induced hum.  Unfortunately, the hum I usually experience is not from magnetic fields, but from electric field interference that's capacitively-coupling to the pickup windings, and unless the pickup has appropriate E-field shielding, magnetic-field counter-measures (e.g. bucking coil windings) will have no effect.

Fortunately, E-field shielding is pretty straight-forward.  What you want to do is provide enough shielding (i.e. conductive surface tied to ground) near the pickup so that the majority of the electric field interference is shunted (via capacitive coupling) to this surface, rather than to the coil(s) of the pickup.

For further reading, check out the capacitive-coupling section in Chapter 2 (Cabling) of the book, "Noise Reduction Techniques in Electronic Systems, Second Edition", by Henry W. Ott.  Great book!]

This amount of shielding will have some effect on the sonic properties of the pickup -- essentially, it appears as extra capacitance from the pickup to ground.

In this case, my shielding added about 0.5 nF to the output of the pickup.  Given that the tone-control's capacitor is 47nF, and that I usually play with the tone control near 0 ohms (i.e. fully, or nearly so, ON), this additional amount ( 1 % ) would seem to be insignificant.


An Aside on the Pickup's Placement

OK -- the bass sounded pretty good!  And I was wondering how the pickup was placed relative to the 12th fret.

The centers of the neck-side poles measured roughly 13 inches from the hump-top of the 12th fret.  That's very interesting, because, according to internet sources, the same poles on a Musicman SR4's pickup are about 13.125 inches from the 12th fret.

In other words, the placement of this humbucker is within 1/8 inch of an SR4's humbucker.  Maybe this accounts for its sound?

I was also quite surprised, because from the pictures, I thought that the pickup was higher up, placed in a position close to where a P-bass's pickup would be.  And then I looked more closely...

Hmmm -- although the pickup is placed next to the pickguard, the bridge is actually fairly far away from the rear end of the guitar.

And the neck has 22 frets, not 20, and the neck pocket isn't as "long" as a typical Fender pocket.  That is, the neck juts further out of the pocket.  (This also means that I cannot replace this neck with a neck drilled with the standard Fender hole pattern -- it won't sit far enough into the neck for its holes to line up with the body holes).

The overall net effect of these changes is that the neck and bridge have been shifted in position towards the neck-end of the body, which is the same as if they'd not been changed, but the pickup had been moved instead from the standard P-bass position to one closer to the bridge, similar to a Musicman pickup position.  But now the bass is roughly 1 3/4 inches longer than my P-bass.

I'm happy with the sound, let's continue on...


Working on the neck and headstock.

First, let's take care of that ugly headstock.

Not a lot of wood to work with, but what the heck.  Tackle first with a saw, then a sanding bit on my drill, then file and sandpaper.  Here's the result:

Much better!

Here's the bass in its fully assembled yet unpainted state:

I then removed the neck and its hardware, and then finished the neck with brushed-on Minwax Fast-Drying Polyurethane (clear satin) and hung to dry.  Once dry, I sanded down with 1000 grit sandpaper.


Painting the body

Now to paint, sand, and then polish the body.

Again, just like my previous project, I'm following (pretty much) the steps in the book, "How to Create a Factory Guitar Finish with Just a Couple of Spray Cans!", by John Gleneicki.

1.  Strip the body of all parts. 

2.  Sand the body and then fill any small dings and divots that I found with auto-body bondo.

3.  Spray the body with a can of Spraymax 2K Glamour High Gloss Clear Coat to act as a body sealer and filler.  Here's the body after this step:

The red spots on the body are bondo patches.  (The wood is so soft that it dents if you look at it sideways.)

4.  Sand the front and back of the body flat with a wood block and 320 grit (dry, not wet).

5.  Because the body wasn't too flat to begin with, this last step resulted in me sanding back to wood in a few spots.  So I sprayed another can of the Spraymax 2K and repeated the leveling of front and back with block-sanding using 320 grit (dry).

6.  Wait 3 days, then spray with primer.  When dry, lightly sand with 600 grit (dry).

7.  Spray the color (base) coat. 

Here's the primed body, waiting for base coat, in my homemade painting jig (jig described here: http://k6jca.blogspot.com/2014/07/bass-guitar-body-painting-jig.html

8.  Wait 2 days, spray with a can of Spraymax 2K Glamour High Gloss Clear Coat over the color coat.  Note: you don't need to sand the color coat if using urethane color coat.

9.  Wait another day, then sand with 600 grit (dry) and spray another can of Spraymax 2K Glamour High Gloss Glear Coat.

10.  Wait a week.

Before we continue on, let me add a few more pictures.

Here's a shot of the types of paint I used.  Middle can is the base color:  VW "Mellow Yellow", custom mixed at "Jerry's Paint and Supply" in Sacramento.  PPG code 902738.

The Spraymax can has a slightly different label from the cans I used last year: now there's "368-0061".  No idea what that means.  New formulation for California?

My painting worksheet.  Click on it to enlarge.

A tip!  If using a trigger-handle for your cans, tape it to the can.  I found that cans could rotate in the handle, and if I wasn't paying attention I'd end up painting the inside of the trigger-handle, rather than the body.

Sanding and polishing the finish

A week has passed.  Time to remove the neck stick and start sanding.

Body before sanding begins:

First, I'll note that all of the sanding is done with wet sandpaper.  I start by soaking the sandpaper in a bowl of water for a few minutes, then, while sanding, I'll frequently dip the paper back into the bowl to keep it moist and to clean it off.

This means that the body gets pretty wet!  It's important that this water not get into any holes, as the wood will swell and you can easily sand through your coats.  This time I plugged them with wax from a candle -- I let melted wax drip over each hole, and while it was still soft and malleable I pressed it into each hole.  I then gently scraped away the remaining wax (use fingernail or soft tool).

This worked very well -- no unintended swelling this time!

Regarding the actual sanding,  Gleneicki goes into a good amount of detail in his book, so I'll just summarize what I did:

1.  Sand top and bottom (but not the tummy and arm contours) with 320 grit, wet, using a wood block.

2.  Sand top and bottom and tummy/arm contours with 400 grit, wet.  No block (paper held in fingers).

3.  Sand the above, plus sides (but not edges), with 600 grit, wet, no block.

4.  Sand the above, plus gently-rounded edges, with 800 grit, wet, no block.

5.  Sand the above, plus sharply-rounded edges, with 1000 grit, wet, no block.

6.  Sand all of the body with 1500 grit, wet, no block.

7.  Sand all of the body with 2000 grit, wet, no block.

Ooops, a boo boo!

While sanding the sides, all of a sudden I saw white primer (probably because I actually used 400 grit on the sides and also didn't adequately spray on the second day's clear coat.  Next time, 600 grit!).

Heart stop!

(Click on image to enlarge)

Can I fix it?

Fortunately I had a bit of paint left in the can (tip:  don't spray it all out when painting the body.  Leave a little in the can, just in case).

So I masked off the body, revealing only the primer and a bit more of the body around it...

...and sprayed it with color: 2 tack coats, 3 (or was that 4?) wet coats.

After the paint had dried, I sanded down its edges and then added an enlarged mask for a new layer of clear coat (fortunately, I had purchased an extra can of Spraymax 2K.  So the cost to fix the boo-boo:  $20!).

(Clear coat:  2 tack coats, 4 wet coats).

Here's the body, waiting for the clear to cure.

After a few days I removed the mask.  If you look closely, you can see the edges of the new clear coat.

(Click on image to enlarge)

I then sanded the new clear coat patch, removing its "orange-peel" and blending its edges, first with 1000 grit, then 1500, then 2000, all wet.  Here's how it ended up:

Looks pretty good to me!


Polishing the finish:

After the final sanding with 2000 grit, I polished with Turtle Wax "Polishing Compound" that I'd picked up at a hardware store.  Rubbed and sweated, rubbed and sweated, rubbed and sweated (hey, it's summer, and it's been hot and humid recently!)

Finally got it to a point that I was satisfied with it.  The surface isn't as flat as I'd like it to be (i.e. perfectly flat), but it has a nice mirror-like sheen.

Here's the end result:

Not too bad!


Final Thoughts:

1.  The new Spraymax 2K seems to take a bit longer to cure (but I could be wrong).  I have some very small dings in the body where some hard objects pressed into the body (such as my car keys in my pants pocket) while I was holding the body against me and aggressively polishing its sides.  Not a big deal, but maybe try 2 week cure before starting sanding?

2.  In the same vein, pot life in the can seems to be longer than 24 hours.  With the can I used to fix my mistake, I noticed that it seemed good at least 48 hours afterwards (and perhaps 72?).  Again, perhaps it's a new formulation?

3.  Next time, I might try sanding with higher grits before I begin polishing.  Perhaps 2500 or 3000.

4.  Don't use bondo to fill holes -- it shrinks as it drys, and thus can sink.  Use bondo for shallow dents and dings.  Fill holes instead with wood dowels.


And the standard caveat:

This is a learning process for me.  Never assume that what I've done is the best way to do it, or even the correct way.  Use your own judgement and common sense.  Or ask an expert.

And if you know of a better way to do something, please let me know.  I'm always interested in learning new tips and techniques!

And one more thing...if you're thinking of buying a kit to save money, don't do it!  You can get a decent guitar, used, for less money than you'll spend on the kit plus paint plus tools.


Links to Bass posts of mine...

Sonic Blue Bass (part 1 of a 3 part series)

Mellow Yellow Bass

Short-scale Telecaster Bass

Bass Guitar Painting Jig

Repairing a G&L Butterscotch Blonde Paint Chip

G&L ASAT Bass Strap-button Extender

Bass Guitar Body Painting Jig

When I painted a bass guitar body last year, this was the technique I used (described here:   http://k6jca.blogspot.com/2013/09/building-bass-guitar-kit-part-2.html):

Not a great way to do it.  The bass body was awkward to hold, and the paint layers around the bottom edge were too thin because of the difficult painting angle.

So, when I recently decided to paint another bass body, I thought it best to make some sort of jig to hold the body during painting.

Here's what I came up with, using materials purchased at the local hardware store:

 

 

During the painting process (e.g. primer coat, base color coat, and clear coats), the body is mounted to an assembly that is never removed.  This assembly consists of a neck stick (short length of hardwood, attached to the neck via the body's neck holes).  And as part of this assembly this stick is attached, in turn, to an 18" length of 1/2" pipe, using a pipe flange and some couplings.  This pipe allows me to rotate the body in the jig and also lets me hang the body vertically while a paint coat cures.  More on this later.

Here I'm holding the "neck stick assembly":

Here's the basic jig with the bass body and its "neck stick assembly" removed.

To build this jig I used the following materials:

The base mounting wood is a piece of Melamine Shelving (23 3/4" x 48" x 3/4").  But any scrap wood of the appropriate size should be fine.

Two 1/2" Floor Flanges are attached to this base.

The vertical pipes are each 1/2" x 36" threaded pipes.

These each go into one end of a 1/2" Tee.

The horizontal member between the two 1/2" Tees is a 1/2" x 12" threaded pipe.

And into the top of each Tee is screwed a 1/2" x 1" length of threaded pipe.

All of these pipes are screwed down tightly!

I've screwed a 1" x 1" x 1/2" PVC reduction Tee onto the tops of each of the two 1/2" x 1" threaded pipes.

Here's a closeup of the left-hand one.  Short lengths of 1" Schedule 40 PVC pipe are glued into each end of the Tee.

 

And here's the other PVC Tee.  I hacksawed slits into the PVC piece glued into the left-side of the Tee,  and I placed a hose clamp over the slits.  This hose clamp, when tightened, securely holds the body at any rotational angle I desire.

Here are the two floor flanges, with the vertical pipes screwed into them.  I tightly attached the pipes to these flanges (and built the rest of the jig) before I mounted the flanges onto the bottom piece of wood.

 

To keep the jig from rocking on the nuts holding the flange screws to the bottom-side of the wood mount, I attached lengths of inexpensive 11/16" x 2 3/8 furring strips along the bottom sides of the wood mount.

Here's the assembly that attaches to the base body:

I've attached a 1/2" floor flange to the "neck stick"

A short length of 1/2" threaded pipe attaches the floor flange to a 1/2" Tee.

Into the Tee is threaded an 18" of 1/2" threaded pipe.

(Tighten down all these joints!)

I also screwed in a 1/2" PVC threaded coupling into the 1/2" Tee, and into this coupling I glued a scrap piece of 1/2" PVC pipe.  This the handle I use to rotate the bass body.

By the way, if the hose clamp is really tightened down hard, the 18" pipe won't move while you rotate the body.  NOT GOOD -- this means that pipe is unscrewing from the Tee attaching it to the bass' "neck stick" when you are rotating it.  Worst case:  the body will unexpectedly fall to the ground.  

Oops!

So I added a little note to remind myself not to over-tighten the hose clamp.

After the body is painted, I hang it vertically to dry.  To do this, I made a hook assembly that I can screw onto the end of the 18" piece of 1/2" pipe that is part of the "neck stick assembly".

Here's what the hook assembly looks like:

I drilled a hole in a 3/4" threaded PVC cap and then attached a hook.  A 3/4" x 1/2" PVC bushing is then threaded into the cap.

There's a nut on outside of the cap (see picture above) and a nut on the inside (and you can also see internal threads of the PVC bushing).

Here's the hook assembly screwed onto the end of the 18" pipe:

 And here's the body, hanging to dry after I had applied its sealer coat.

Here are some pictures of the jig in action, in my home-made paint booth (using inexpensive 9' x 12' paper drop "cloths" above and below):

Primed body, awaiting color:

 Color coat being applied (Volkswagen "Mellow Yellow"):

Another shot of the paint booth.  The inexpensive paper awning is thumb-tacked to a wooden arbor and the paper, where the thumb-tacks penetrate, is reinforced with short pieces of duct tape, so that the paper doesn't rip.

That's it!

Update:

There's an interesting discussion on the Talkbass forum  regarding this jig and others (there are some very clever designs).  You can read it here:

    http://www.talkbass.com/threads/jig-for-painting-a-bass-body.1092902/


Links to Bass posts of mine...

Sonic Blue Bass (part 1 of a 3 part series)

Mellow Yellow Bass

Short-scale Telecaster Bass

Bass Guitar Painting Jig

Repairing a G&L Butterscotch Blonde Paint Chip

G&L ASAT Bass Strap-button Extender

Modifying a 75 ohm HP 85046B S-Parameter Test Set to be 50 ohms

A while ago I purchased an HP 8753A Network Analyzer to replace the HP 8505A Analyzer that I had been using in my home lab.  But I'd been delaying putting it into that rack where the 8505A has been, because I first wanted to get a 50-ohm S-Parameter test set for it.

The thing is, S-Parameter Test Sets for the 8753A, such as the 85046A, are expensive, and I'm cheap.

Recently I visited a friend, Dick (W1QG), who also has an 8753 Network Analyzer, and he showed me how he had modified a less-expensive 8503A (the S-Parameter test set for the 8505A analyzer) to work with the 8753.

He had added a latch and a one-shot to the 8503A (to generate the 200 msec Sweep-Delay signal for the 8753), and the circuit looked straight-forward and easy to implement. 

Dick mentioned, too, that although the 8503A is only spec'd to 1.3 GHz, he could operate his up to around 2 GHz with minor correction factors.

Sounded like a good approach.  And I had an 8503A.

The next day, though, happened to be the De Anza swapmeet in Cupertino.  And while walking its aisles I came across an 85046B S-Parameter Test Set.

Although directly compatible with my 8753A Network Analyzer (unlike my 8503A), this Test Set had a number of issues, the first being that it was 75, not 50, ohms.  Also, the seller told me that he'd removed its "Transfer Switch" (that's the coaxial relay inside it), and overall operating condition was unknown.

On the other hand...it was cheap!  And an idea hit me: rather than build the interface circuit that Dick had designed into my 8503A, would an easier approach be to somehow combine the 85046B's interface with my 8503A?

I had no idea if I could or couldn't, but the price was right, and I thought it would be fun to investigate.  So home it came with me.

Replacing the Missing Parts...

Fortunately, the Operating and Service Manual for the 85046A/B is available on the internet  ( Click here for manual).  Looking it over, it became clear that, with the exception of the 85046B's Bridge and Bridge/Splitter modules, everything else in the 75 ohm box was actually 50 ohms

I also noted that the 85043A/B had a 0-40 dB step attenuator (10 dB steps) that the 8503A did not have.

Comparing photographs in the 85046A/B and 8503A service modules, the Bridge and Bridge/Splitter modules looked very similar.

Hmmm...rather than modifying the 8503A to work with the 8753A, if I instead modified the 85046B to be 50 ohms, I'd already have (with no work on my part):

1. A fully functional interface designed specifically for the 8753A.
2. The 40 dB step attenuator.

And of course, it wouldn't hurt that the four N connectors for attaching the 85046 to the 8753 would properly line up with the 8753's four N connectors (unlike the 8503A).

It looked like all I needed to do would be to transfer the 50 ohm Bridge and Bridge/Splitter from the the 8503A to the 85046B!

Before I progressed further, though, I needed to replace the missing parts.  For the Transfer Switch (coaxial relay), I could have taken the one out of my 8503A, but that one was only rated to 1.5GHz (HP p/n: 08503-60035), while the proper one for the 85046A/B is rated to 18 GHz (HP 08503-60051).

Also, I discovered that one of the internal metal coax interconnect cables was missing. Fortunately, using the manual I found its part number (HP 85046-20009).  I Googled it and quickly found a company who could sell me both the cable and the Transfer Switch.

While they were in transit I looked over the 85046B manual further and discovered that there were two flavors of Logic boards; one board is designed to for use with a mechanical transfer switch (like the one I'd ordered), and the other is designed for use with a solid-state transfer switch.

The main difference between the two boards is the difference in the timing of the "Sweep-Delay" pulse generated for for the 8753 Network Analyzer whenever the Transfer Switch or Step Attenuator is changed (per this illustration):

(Click on Image to Enlarge)

Well, the board in my 85046B had a part number of 85046-60016.  Unfortunately, this was the board designed to work with  the solid-state transfer switch.  But I had the mechanical transfer switch, and so I really should be using the other logic board (HP 85046-60051) to create the proper 200 msec. Sweep-Delay pulse for the 8753A:

Fortunately, the PCB is common to both Logic boards, and there's only a slight difference in component values. Here's a summary of those differences:

        Solid-State Switch     Mechanical Switch
          (85046-60016)          (85046-60051)
   R7     39 ohms                  56 ohms (2 watts)
   C2     4,700uF, 35V         10,000uF, 35v 
   R25   0 ohms                    unstuffed
   R5     0 ohms                    unstuffed

So changing a -60016 board into a -60051 board couldn't be easier.  I just lifted one end on both R5 and R25 and called it a day.

(I lifted one end of each resistor, rather than removing the resistors entirely, so that I could easily convert the board back to its original state, should I ever need to.  And I didn't change R7 and C2 because they did not seem critical to me.  Given that the transfer switch's coil resistance is 200 ohms, I couldn't see a good reason to change R7 to 56 ohms.  And, although I would have replaced the 4,700uF cap with a 10,000uF cap if I'd had one, there wasn't one in my junk box. So I left it unchanged.)

Here's the new Transfer (Coaxial) Switch

Replacing the Bridge and Bridge/Splitter...

The next step was to remove the 75 ohm Bridge and Bridge/Splitter from the 85046B and replace them with the 50 ohm Bridge and Bridge/Splitter from my 8503A.  Here are the steps.  Apply to both the 85046B and the 8503A:

1. Disconnect the SMA connectors attaching the RF plumbing to these two modules.
2. Remove the four screws (and, where used, the four white shoulder-washers) holding each module to the chassis.
3. Unplug from the PCB the single wire that goes to each box. 

Below is pictured one of the 75 ohm modules and one of the 50 ohm modules.  Physically they are identical (with the exception of the Test Port connectors on the right side, of course).

75 ohm unit from 85046B is on the top.

50 ohm unit from 8503A is on the bottom. 

I also moved the Blue and Gray wires from the 75 ohm boxes to the 50 ohms boxes (the wires attached to the 8503A modules are not long enough to attach to the Logic board in the 85046B).

And then I installed the 50 ohm Bridge and Bridge/Splitter into the 85046B, making sure that the modules were the appropriate side up so that the SMA connectors all aligned properly.

To summarize, if you have an 8503A gathering dust, using it to convert a 75 ohm 85046B to 50 ohms is very simple.  Here is all that I did:

1. I replaced the 85046B's 75 ohm Bridge/Splitter (p/n 5086-7448) with the 50 ohm Bridge/Splitter (p/n 5086-7240) from my 8503A.  
2. And I replaced the shorter yellow wire on the 5086-7240 with the longer Blue wire from the 5086-7448.
3. I replaced the 85046B's 75 ohm Bridge (p/n 5086-7449) with the 50 ohm Bridge (p/n 5086-7229) from my 8503A.  
4. And I replaced the shorter light-brown wire on the 5086-7229 with the longer Gray wire from the 5086-7449.

Here are the 50 ohm Bridge and Bridge/Splitter installed in the 85046B

A work in progress...

 

My initial testing (network analyzer not calibrated, so no correction factors have yet been applied)...

S11, open circuit:

S11, 50 ohm load

It seems to work!  I don't expect to get the full range of operation that an 85046A would give (to 3 GHz), because the 8503A modules are only spec'd to 1.3 GHz.  But, for me, this was a quick way to get an inexpensive, yet acceptable, S-Parameter Test Unit for my 8753A analyzer.

Addendum, 1 July 2015:

In the comments section below, David Kirkby,G8WRB mentioned a problem he had with the lid of the 8505A bridge missing the required four tapped mounting holes.  He sent along the following picture to illustrate the issue:

The unit on the left is the 75 ohm bridge from his 85046B.  Note the four mounting holes, circled in red on the case "lid".  This are missing from the 50-ohm 8505A unit on the right.

As Dave points out, the fix is straight-forward.  Just swap the two lids.

(I don't recall having this issue, myself.  But just in case I did and forgot about it, I'm glad Dave reported it.)

Note (8 Octobor 2020):

For another take on modifying an 85046B to 50 ohms, see this blog post:

http://k6jca.blogspot.com/2020/10/hp-85046b-conversion-to-50-ohm.html

Caveats!

Standard caveats apply!  Know what you are doing.  Don't assume what I've written is correct -- I might have mistyped or made other mistakes.

Building a Bass Guitar Kit, Part 3

(You'll find Part 2 here: (click here!))

OK -- the body is painted.  All that is left now is to sand and polish it.

As with the painting described in the previous blog post, I will strongly recommend John Gleneicki's book, "How to Create a Factory Finish with Just a Couple of Spray Cans!".  There are also some YouTube videos you can watch (for technique).  You'll find plenty on YouTube.  One series I like is by Joseph Tubb (although much of what he does in his series is not applicable to this project).  But for sanding and polishing technique, I recommend checking out parts 7 and 8 of his series.

Part 7 is here: 

(Click HERE for Video)

And part 8 is here:  

(Click HERE for Video)

I used sandpaper grits of 600, 800, 1000, 1200, 1500, and 2000 (all sanded wet, not dry).  These finer grits were available at the same auto-paint store where I purchased my paint.

(Click on image to view in its entirety)

Here are examples of the shine as I worked.  Note that the reflections of straight edges aren't exactly straight, indicating a very slight waviness in the overall finish.  I'll try to do better on my next body!

(Click on image to view in its entirety)

One problem with using wet sandpaper -- if you aren't careful, water can get under the paint and cause swelling.  Here's an example of what happened when water got under the paint at one of the holes where I'd originally screwed the body to the "stick" (which was then removed for these last sanding steps):

(click on image to view in its entirety -- the problem is to the right)

I also had water get under the paint at some of the pick-guard screw holes.  Fortunately, drying out the area with heat (and applying pressure, such as pressing hard with thumb) can bring the raised areas back down.  I used an incandescent bulb about 6 inches from the surface to dry out these types of mistakes.

By the way -- you might first try plugging holes (and covering open areas, such as the one above) with, say, candle wax, to waterproof them.

Another caution:  if using a wood sanding block, the wood can warp if it gets wet, and your flat block will no longer be flat!

After sanding, I used a swirl remover (Mequiar's, shown below), follow by a 3-M rubbing compound (not shown).  Both were purchased at the Auto Paint store.  The foam polishing pad came from Stewart-MacDonald.

(Click on image to view in its entirety)

When the body was polished to my satisfaction, it was on to final assembly, followed by bass setup.

For bass setup, I recommend first checking out the four great videos by John Carruthers on YouTube, in which he explains the steps necessary to setup a bass guitar:

First:  Truss Rod Adjustment:   

(Click HERE for Video)

Second:  Bridge Action Height Adjustment:     

(Click HERE for Video)

Third:  Nut Action Height Adjustment:     

(Click HERE for Video)

Fourth:  Intonation Adjustment:   

  

(Click HERE for Video)

For reference, here's my summary of the setup steps shown in the four videos above:

1.  Truss Rod
     o  Capo at first fret
     o  In playing position, fret the E string where the neck joins the body (16th fret?)
     o  At about the 7th fret use a 0.015" feeler gauge to measure string height above fret.
            To raise string, turn truss rod counter clockwise.  Opposite to lower.

2.  Bridge height
     o  Remove capo.
     o  In playing position, at the point where the neck joins the body (again, 16th fret):
            Adjust E-string saddle screws so that the string is 4/32" above the fret.
            Adjust A-string saddle screws so that the string is 3.5/32" above the fret.
            Adjust D-string saddle screws so that the string is 3.5/32" above the fret.
            Adjust G-string saddle screws so that the string is 3/32" above the fret.

3.  Nut Action Height
      o  For each string:
             Measure height above the first fret.  If greater than 0.022":
                  Loosen string and remove from nut groove.
                  With appropriate file, file in a slightly downward direction (towards tuner) until

                  desired string height reached.

4.  String Length
       o  In playing position, adjust the Saddle Length Adjusting Screw so that the open note and

           the fretted octave are the same.

By the way, during the final assembly and setup I found a few more problems:

1.  Some pick-guard screw holes are stripped (nothing done at the moment, the screws seem to be holding fine).

2.  Truss Rod difficult to adjust.  This neck's truss rod seems to be angled down slightly, so only the short end of the hex driver can engage it, rather than the long end.  Unfortunately, the small diameter of the hole in the wood means that the hex driver can only subtend a small angle of movement when adjusting the truss rod.

3.  During setup, the E string saddle bottomed out.  I fixed this by raising the neck slightly with a shim in the neck picket made with two back-to-back business cards (to get the appropriate thickness):

(Click on image to view in its entirety)

4.  While tuning, I found that the D-string was a little too wide for the slot in the string tree, and it would stick in the slot while I tried to tune it.  The slots were also a bit uneven and had sharp edges at the slot ends (where I was worried about the wire catching).  So I smoothed the front and rear slot entrance/exit edges and widened the two slots with a small file.

Here are a couple of pictures of the finished Bass:

Conclusion:

The bass kit was much more work than I anticipated, from fixing problems that originated at the factory (in China, I believe), to painting the body and dealing with all of the little heart-stopping issues that arose (runs, sand-throughs, etc. etc. etc.), to the extra expense of new strings, guitar-specific tools, etc.

So I have to ask myself, was it worth the effort?

For me, the answer is, without a doubt, yes.

Sure, the kit had numerous issues, but because of these issues, it provided an invaluable (and inexpensive, compared to the price of quality basses) learning platform.  Now if I need to do a bass guitar setup --  no problem!  Frets uneven?  I can handle it.  Sealing, painting, and finishing the body?  A lot of work, but I can now get a color scheme I like, rather than one forced upon me by a guitar's manufacturer.

In short, I'd do this again.  But next time I would prefer that the kit be a lefty PJ bass, or better yet, a lefty Rickenbacker knockoff!

However, if your goal is simply to purchase an inexpensive bass, my advice would be to find a used one.  With the tools and paint that I purchased, I easily spent several hundred additional dollars above the price of the original kit.  For that kind of money, you can get a decent used bass.

I would also like to point out that this kit is a left-handed bass kit, and it's quite possible that a number of the issues I mention in this and previous posts are due to the fact that it is left-handed and thus the workers might not have had experience with any changes-to-procedure that might have been required for the manufacture of the left-handed body and neck.  In other words, the right-handed kits might be better!

Disclaimer:

This was my first time doing any of this:  fret leveling, painting, etc.  Before you tackle your own project, do your research!  Don't depend solely upon my experiences.


Links to Bass posts of mine...

Sonic Blue Bass (part 1 of a 3 part series)

Mellow Yellow Bass

Short-scale Telecaster Bass

Bass Guitar Painting Jig

Repairing a G&L Butterscotch Blonde Paint Chip

G&L ASAT Bass Strap-button Extender