One can never have too many power supplies, especially if one uses older tube gear of either commercial or home brew persuasion. One of the workhorse supplies available these days is the series of HP23 supplies, the HP23, 23A and 23B. I had three in my shop, all pretty sorry for wear and getting rather long in the tooth. I had purchased two variant kits to be used to restore 23's both cost around the $60 dollar range give or take a few bucks. Each kit contained a professionally etched and lettered high quality board and all the components necessary to upgrade these old power supplies and give them another 35 years or more of life. The intent of this piece is not to be a guide to doing these upgrades, the kits are available on line and the instructions for building the kits are there as well. My intent is to describe in general what I did and what my results were. So here goes.
The first Power supply I did was an HP23A, There is a difference between the 23, the A and B but other than involving the switchable 250 or 300 low voltage level and one or the of them not having had a resettable fuse on it. Possibly one of them also did not have adjustable bias voltage I don't remember which, I think it was the original 23. . In any even, it matters little my case as the modifications I made cause them all to be equal in the final product and the power supplies are all basically the same animal with minor variations as to wiring. The HP23A was the first candidate. I upgraded only the 23A and 23B, to the best of my knowledge I've never seen a plain 23. I chose to maintain the features of the 23A and get one up and running correct before experimenting on the others. I used for this first supply Kit HP23R kit which is sold by Mike Bryce, WB8VGE of http://www.theheathkitshop.com/ The R version was an earlier version and Mike now lists an RL version on his site that is said to be smaller and easier to mount. Due to the size of the R board, the supply filter choke is mounted under the chassis. A word of warning to other who wish to undertake updating one of these supplies, if you cannot read a schematic and understand what you are reading, practice on something else first, this is not for novice builders and you do not want to short out the power transformer and damage it, they are unobtainable new and costly in any case.
Both kits I have experience with, use modern snap in electrolytic caps and carbon film resistors all of which are much smaller and better quality than the originals and take up a lot less space. Both have professionally done boards and are easy to assemble, problems , if any, will come in the wiring stage. That said, Mikes instructions are clear, and concise, if one reads schematics well enough to understand which end of a component or which wire is which, little problem should be encountered.
Here is what I did, with the 23R. I first gutted the power supply as directed in the Instructions, one should read the instructions carefully before going wild under the hood. but with the 23R you will wind up with the board mounded atop the chassis on spacers and the filter choke moved under the chassis. It is easy to miss wire the switches and if careful attention is not given to the wiring diagram you will lose the switchable feature or worse case have no power out. However, the board is easy to assemble and the instructions are clear. In addition to assembling and wiring the board I choose the followings mods, I added a on/off switch so that the power supply is not dependent upon the on the power control of the attached rig. As this switch is wired across the control pins that the attached rig uses , it can still be turned on by the rig power control. Testing was straight forward, using a volt meter the various output voltages were checked and all found to be correct allowing for slightly higher Line voltage input. Here is a side view and top view of the R variant the switch on the left is the added on and off toggle.
The second power supply was another HP23A and this effort used an HP23D kit which is sold by Bob Hanway, K8GNZ at www.OldHeathkitParts.com . The D varies somewhat in design from the R variant but both basically do the same thing. Bob has excellent instructions available on his site too and Again I followed the instructions and the kit went together without a problem. The D board is some what smaller than the R variant and it is installed under the chassis. The Filter choke remains in its original place. The Kit comes witha small cover to cover the holes where the original capacitor were mounted. In addition to the changes mentioned in the 23R to this one I added another socket on the backside to facilitate using gear other than heath gear (usually home brew gear) with this supply I can do so with out using the Heath kit wiring protocol. Here are front and side views of the D version.
The third supply that I updated was my original HP23B that I built some 37 year ago to power my HW101 which I still have. Rather than use a kit I elected to buy the parts and direct wire them into place. Mouser supplied all the needed parts for around $35.
The most difficult part of this rebuild was the requirement to stuff the original capacitor cans as the snap ins are much smaller and no easy way to mount them. I opened the cans by cutting around the circumference about 1 inch from the base, with my Moto tool and cutting disk.The cans were then heated and the old capacitors pulled out along with the tar they were immersed in. There are all sorts of descriptions of this process with pics on line so I am not going into a lot of detail here other than to say I closed the cuts between base and can using aluminum tape of the sort used by HVAC folks to seal heating/cooling ducts. I then remounted the cans and wired them in. The diodes and resistors were replaced in a similar manner, The bottom line is this method works just fine and is less costly. However you do not have a nice board to work with and that is a convenience. I can tell no difference in operations between the three versions, Personally I prefer the direct wired version but that is a personal preference based on nothing more than my idiosyncrasy,. your mileage may vary!