Citation I Refurb - Assembling the Power Suppy

My apologies for not posting for almost 3 weeks now.  I started to work on assembling some of the sub-assemblies and simply became too absorbed in that work.  It was a case of "do I write up what I've done so far?" (the choice I should have made) or "it's really fun assembling the parts again.  I think I'll go do some more kit building.  The blog can wait."  So I'm back writing today and I have a large backlog to post.  Unfortunately, my photo hosting site, PBase.com, is down so I won't be able to insert any photos at this point.  But I will add those later.

This is where I am going to begin to deviate from my original stated plan.  The power supply is the one area where there is a modification to the original layout as specified by Harman Kardon.  Jim recommends proceeding one component at a time when installing his kit so that you don't lose track of where everything is installed.  Based on that advice I decided that I needed to do the power supply bracket now rather than continue tearing down the chassis.  In hind sight, that wasn't necessary for me since I am completely rebuilding the entire pre-amp.  I do recommend his advice, however, for those that are simply replacing the power supply section.

 The Jim McShane kit to rebuild the power supply uses different value electrolytic capacitors than the stock components.  The stock capacitors are:

• C103 - 80 µF 250V
• C104 - 80 µF 250V/40 µF 450V dual section cap (C104A and C104B)
• C105 - 40/40/40 µF 450V triple section cap (C105A, C105B, C105C)
• C106 - 1500 µF 35V

The replacement caps are as follows:

• C103 is replaced with a 820 µF 250V cap
• C104A is also replaced with a 820 µF 250V cap
• C104B and C105A are replaced by a 50/50 µF 500V dual section cap
• C105B and C105C are replaced by a second 50/50 µF 500V dual section cap
• C106 is replaced with a 15,000 µF 35V cap

This combination of capacitors requires a relocation of the parts on the bracket and a slight change in the wiring instruction as specified in the assembly manual.  C103 and C104A are stacked on top of each other in the old C103 position using 1 3/4" spacers. (See photo below).  In order to mount the spacers two new holes need to be drilled in the mounting bracket.  These holes are drilled at 90° to the original holes.  This is the only physical modification to the bracket that needs to be made.

The new C104B/C105A dual section cap is mounted in the original C104 position.  The other 50/50 µF dual section cap become C105B and C105C and are mounted in the original C105 position.  And finally, the new C106 cap is mounted in place in the original C106 position.  Because of the relocation of the electrolytic capacitors in the bracket the wiring layout and location of the resistors will differ from the original layout.

Also of note in the Jim McShane kit is the addition of two 0.01 µF capacitors that are mounted in parallel with 105B and 105C.  According to Jim these capacitors are intended to bypass high frequency noise and quiet the phono section.

For someone like myself, who does not have a solid skill in reading electrical schematics, it is fortunate that Jim includes numerous photos of a newly assembled power supply bracket using his parts.  By carefully looking at the supplied photos and comparing them to the Citation I schematic I was able complete the bracket with a high degree of confidence that I did it correctly.  This required a few e-mails to Jim McShane to confirm a few details, but he's a good guy and always seems willing to help out his customers.

The rest of the parts for the power supply bracket are fairly standard replacements and can be assembled according to the original Citation I assembly manual.  The only deviation of parts are the original "top hat" diodes.  These are no longer available, but that is not an issue as the replacement fast/soft recovery diodes that Jim supplies in the kit are far superior to the originals.

A new rubber grommet was installed in place of the original, which was dried out and hard and had to be cut out as it had no flexibility left.  Note that the mounting bracket holding the C105B/C105C dual section cap was slightly altered to accommodate the grommet hole.  Look above at the photo showing the new cap stack.  See the little bracket foot that slightly obscures one of the original mounting holes?  Now imagine the same thing happening on the backside with the mounting bracket that is next to the rubber grommet.  One of the bracket feet slightly covers the hole through which all the chassis wires need to feed.  This was easily solved by using a Dremel tool and a grinder bit.  The foot was quickly ground off.

Compare the photos below of the newly assembled bracket with the original.  Note that the 3.3 ohm resistors (3.6 ohm in the original kit) are not installed at this point (between the diodes CR5/CR6 and the bottom left terminal strip.  The bolts of the transformer come up through the chassis and then through the power supply bracket.  The attachment location for the bolts from the transformer are located under the resistor positions.  So these resistors will be added after the bracket is attached.  I will also dress the 0.01 µF capacitors neater by bending them up later when completing the chassis wiring. See how they are currently layed out in a butterfly position.

Total time spent:  ~4 hours