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Heathkit HP-23 Rebuild





The HP-23 that I purchased was part of a SB-101 transceiver, SB-610 station monitor and SB-600 speaker (all for $150!) When I got the units home, I decided to restore all of them back to near factory condition.  This is a collection of my notes as to what I have found in terms of replacement parts and paint options and other tips and tricks I learned along the way.

Here are some photos of the power supplies initial condition.  This thing looked liked it lived in a Electrolux! I didn't even try to turn it on, not even with a Variac. I decided it wasn't worth the trouble since I was going to rebuild it anyway.


The top of the transformer is a nicely coated with a good layer of rust







Dust,  spider webs and more dust


At least the bottom looks a bit cleaner.



Disassembly


Here is what the power supply looks like taken apart. Basically,  I now have a Heathkit to build. Not much to it once it is in pieces.  The electrolytic capacitors measured ok in terms of capacitance, but their ESR was very high for them.  



The 100K bleeder resistors all were way out of spec. They measured:

Value

Measured Value

100K Ohm

124.66K Ohm

100K Ohm

115.824K Ohm

100K Ohm

119.180K Ohm

100K Ohm

118.496K Ohm


Capacitor Rebuild



Using a large tubing cutter, I was able to open the cans up. I didn't like the way the tubing cutter "crimped" the edge of the cans.  I may use a lathe on the other two as to not damage them as much. Update - I was able to fix the "inward flare" by taking a 15/16" Sears Craftsman socket and placing it in the can and lightly tapping the edge with a rubber mallet.  This smoothed out the edge perfectly.

I then used a heat gun to heat the cans up a bit so the innards would slide out.  I recommend doing this outside - they really reek.  You know that smell of antique radio, that unique scent common to most older radios? The scent that says "Say, there must be a antique radio in this room somewhere - I can smell it!"  Well, it's the capacitors.  Take one apart someday and take a small whiff.  You'll know what I mean. 

I ordered modern caps from Mouser to put inside the old cans. I'll use some aluminum tape to join the top and bottom halves together.  Once the paper covers are placed back on, you'll never know the difference! (hopefully)




Here's a closeup  of the edge after I straightened out with a 15/16" socket. These things were  also full of tar . It took many cleanings with gasoline and "Goof Off" to get it all out. (Worst part was, the dog decided to roll in my dirty rags and get it on her head.  The gas had pretty much evaporated so it was just the smelly tar that she had on her head. I swear, Yellow Labs are the most loyal, lovable dogs in the world, but they have a sack of potatoes for brains.)





Now we have all the parts to make a "new" can cap.

New cap is rated 150uf/450V at 105 Deg C. Sorry that doesn't show up in the picture.






Here is the new Cap mounted on the old base. I cut off the aluminum feeder strips, then I drilled two holes, one near the ground lug and one near the original pos lead and then soldered them to the lugs on the bottom side. I put some heat shirnk on the leads for the heck of it.
.




Bottom view




Here are the top and bottom. You can see where the leads from the cap are now wrapped around the lugs.





Taped together with aluminum tape. 




With the paper sleeves on. Which one is the original and which one is the rebuilt one? Hint: I need to clean the flux off the lugs on the right one.

  • Old capacitor was rated 125uF 450V at 85 Deg C
  • New capacitor is rated at 150uf 450V at 105 Deg C








Paint!


I was able to get my HVLP sprayer working today and was able to shoot the bottom plate of the HP-23 power supply.   Here is what I did:

  1. Stripped the paint off with paint stripper. Two applications didn't not take it all off. On to step #2
  2. Sanded the rest of the paint off with a palm sander.
  3. Cleaned the surface off with lacquer thinner.
  4. Primed the surface with 2 coats of Lowes Valspar  interior/exterior primer .
  5. In order to give it some texture I used some Rust-oleum texture paint.  I tried the "hammered" paint, but it does not have a 3D effect, It is only 2D. It is very flat, no texture.  I need to try the Rust-oleum American Traditions Stone spray. But I'm thinking that may have too much texture.
  6. Two top coats of my Home Depot Blend. 
  7. Finished off with a light coat of lacquer gloss to give it some sheen.
 
Between steps 5 and 6 I wanted to try out Glen Zooks, K9STH formulas to see how they would match. I knew that the Heathkit colors were not very uniform and I may not have a good match.

So I went to Sherwin-Williams and asked them to scan the chassis and then compare it one created by Glen, K9STH (His paint formulas are here ->http://k9sth.com/uploads/Boat_Anchor_Paint_article.pdf .  The guy behind the counter seemed to think that K9STH's formula would match better than what he had scanned.  I guess it is like the guys in the movie "The Matrix" - they can see people and things in the numbers rolling down their screens.
 
I came home with a quart of "Apache Green" and  tried it out.  It was a bit too dark. This was probably one of Heathkits variants.  I  had a another paint sample that was made up at Home Depot and that matched up almost perfectly.  I finished it off with a light coat of clear lacquer gloss to give it a bit of sheen.

Here you can see the newly painted bottom plate (the one with the slots) up against the side of the original cover.


Another View  - The bottom plate is really glossier than it looks. And the original cover isn't as shiny as the photograph makes it out to be.  





The next thing I tackled was the power transformer cover. It was completely rusted. I used a power drill with  a fiber abrasive wheel to remove most of the rust.  The inside corners required a bit of rolled up sand paper.  The paint job here was a bit simpler:

  1. Sanded off the rust/paint
  2. Cleaned with lacquer thinner
  3. Primed
  4. Painted with high gloss black lacquer

Here is the cover screwed down to the bench so it is easier to sand.










The only real problem I had was removing the four bolts that held the covers and laminations together. The first one came out fine, the next three all sheared off.  Two of which I was able to hammer out of their holes.  The last one was a royal pain in the a@@.  I eventually had to drill it out.  The potting material had glued it so tight it was never coming out.  All this to paint something no one will ever see once it's assembled ...







Assembly!  (finally)

Fresh paint and all the parts ready to go.








New power plugs (from Radio Daze)





Before you email me and ask why the color changed, let me explain.  All the previous photos were taken with the flash on the camera.  This photo below was taken with ambient room lighting.  The lights are fluorescent which will make things look different.