This section is provided thru the graciousness of Ray Vasek, W2EC, and is used here with his permission.

This is an article I submitted for the Hollow State Newsletter. While there is much info passed around via the internet these days, a good source of written material can still be invaluable. If you are at all interested in the classic vacuum tube radios, I highly recommend a subscription to the Hollow State Newsletter.

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Recently I had the good fortune to obtain a relatively clean SP-600. Although a ham for over forty years, this was my first SP-600 and I was completely unfamiliar with it except for what I’d read in magazines or e-mail reflectors. The problem area mentioned most often was the BBOD, or BlackBeauty of Death.

While waiting for delivery of my radio, I tried to gather whatever information I could in anticipation of a major recapping. While I received lots of good advice and ideas, I didn’t come up with a really concise description of just how many and what kind of caps I should plan on replacing, nor the effort that would be involved. I decided that I would try to keep a detailed log of what I did and the order it which it was done, with the intent of providing some detailed information to help make the recapping process easier for others facing an SP-600 for the first time.

Keep in mind that this is the first, and only, SP-600 I have worked with. I do not pretend to be an expert on them, I am only relating the experiences I have had while working on this one particular radio. Additionally, there are many different models of the SP-600 and there may be various minor differences in the electrical configurations. Some differences may even appear within the same model, for example, my radio is an SP-600 JX-6, and one person who used my data while doing his SP-600 JX-6 was not able to locate a few of the capacitors I identified. So use this as a general guide only and be prepared for things to be a little different than I spell out, especially if your model is not a JX-6. However, a look at the schematics for several different models shows the same basic design to be followed throughout the series. Also, this is not a history of the various SP-600 models or an attempt to define the "best" capacitor to use. I’ll leave that to those who are more familiar with the SP-600.

First off, many may ask, as I did, just what is a BBOD and what goes wrong with them?

The BBOD is a tubular capacitor, dark gray or black in color with numerous colored bands to identify its value and rating. It looks like a very large old style carbon resistor that might be in the 5 watt class, roughly 3/4" to 1" long and 3/8" to 5/16" in diameter. The name Black Beauty probably comes from the appearance of those caps most often encountered, a body molded of a shiny black material, and the Death moniker comes from the fact that almost every BBOD you encounter will fail, having very poor (high) leakage characteristics. (Later word has it that Black Beauty actually appears to be a real name, a trademark so to speak.) A large number will even have major cracks in them exposing the insides of the capacitor to the air. Some will be almost completely split in half.

These splits usually occur along the length of the capacitor. Don’t mistake the sealed seam of the capacitor for a split. When you see a split, you’ll know it! Figure 1 shows a pair of capacitors that appear to be in good solid shape with the colored bands plainly seen. Figure 2 shows another pair with splits running the length of the capacitor. While the split capacitors were obviously bad, a test of the "good looking" capacitors showed they were in as poor shape leakage wise as the split caps.

The net is, when it comes to BBODs, just perform a wholesale replacement while you have the radio on the bench.

Figure1 (click on thumbnails to see full sized)

One thing you should be aware of. There are some lucky people out there who will not have to endure the recapping procedure. At some point late in the SP-600 life cycle, at about s/n 17,500, it was apparently recognized that the BBODs were experiencing a high failure rate after years of service. The specifications were then changed and ceramic disk capacitors were used in place of the BBODs. I’ve not seen any reference to similar failures in the ceramic disk equipped SP-600s. So before you start worrying about doing a recapping, check and see if you are one of the few lucky owners of an SP-600 with factory original ceramic disks!

Now that we have decided we should replace all the BBODs, just how many do we need and what types and values are they?

In my JX-6, I found I had thirty-eight BBODs with a value of .01mfd and sixteen BBODs with a value of .022mfd. A check of some later models show a factory change was made to substitute the .022mfd caps with .01mfd caps. This is supported by a military work order authorizing the change, although I can’t reference that MWO number off hand. The consensus is there is no need to get two different values, you can replace all fifty-four caps with .01mfd, although I used both .01 and .022 as called for since I already had them available. There are fifty one caps used for bypass and three used for coupling. In my case I used what I had in my parts bin, .01 or .022 ceramic disks at 1000V for bypass and .01 mylars at 630v for coupling.

Prior to starting the actual recapping, I traced out the schematic locating all the caps as per the parts list.

Once the radio was fully powered up, I found that it had very weak and distorted audio, capable of picking up only a few of the very strong local AM broadcast stations. The bands above 1.34mc appeared dead. At that point I began to make actual changes to the radio.

From this point on I’ll summarize the steps I went through for the re-capping. I did it by trial and error, particularly the error phase, so maybe this will help get you in the right frame of mind for what might at first glance appear to be a daunting task.

At the end of the article is a list of caps along with a description of where it is located. This location is often identified as being at the "cold" end of a component. "Cold" refers to the connection point closest to ground. I've also indicated whether the cap at that position is used for bypass or coupling. Again, I chose to use ceramic disks at 1000v (as I had them handy) in the bypass locations and mylar film at 630v (again because that's what I had available) for coupling caps. I had a note from a couple people who indicated they had the models that came factory equipped with ceramic disks and that not only were the caps changed to ceramics, but the values were all .01mfd, i.e. the .022mfds had been changed to .01mfds. This supports the MWO mentioned previously.

My final summary of caps replaced is sixteen of the .022mfds, of which four were split wide open and thirty eight of the .01mfds, of which fifteen were split wide open, plus the one shorted 10mfd in the 6V6 cathode circuit.

Re-capping an SP-600: Refer to figures 3 and 4 at the end of the article.

In order to make this project appear more manageable I identified seven unique sections for recapping. Except for the underchassis, each section represents an area that requires disassembly of some sort to get to the cap(s) that need replacing. Some areas may contain as few as just one cap to be replaced. I have not provided complete instructions, just tips. Some things may seem strange but if you are looking at the radio while reading these instructions it should become clear how to proceed.

The sections are: 

(1) RF Deck (Fig 3) 

(2) T1 Pod (Fig 3), 

(3) IF transformers (Fig 3), 

2. Loosen the coupler on the Delta Freq control shaft and slid it towards the FCU so the coupler is completely on the long shaft from the FCU.

3. Remove the bracket from the bottom of the FCU that goes to the long spacer near the power transformer. One end is held by a nut at the power transformer. The other end of the bracket is slotted and just slides into a groove on one of the supports for the FCU, so there is nothing to loosen on that end.

4. Unsolder the cap that comes from the FCU to the switch on the front panel.

5. Flip the radio over; locate where the wire harness from the FCU passes through the chassis. Unsolder the wires from their respective terminals. Make notes and keep track of where they attached -- they are color-coded.

6. Remove the four screws that secure the Power Supply filter assembly to its set of spacers and carefully lower the filter assembly, there is no need to unsolder anything here, just support it carefully.

7. With the filter out of the way you can get to the four screws that secure the spacers for the FCU, remove these screws while supporting the FCU so it doesn't fall.

8. Reposition the PS filter assembly and put back in a couple screws to temporarily hold it in place.

9. Flip the radio back over and carefully lift the FCU out, be careful of the long shaft so it doesn't bend and damage the Delta Freq capacitor when removing the FCU.

B. RF deck - refer to figure 3 

4. Unsolder the wires from the RF deck to each tuning capacitor (total of 12 wires, three for each tuner cap section)

5. Unsolder the ground straps from each tuner cap to the RF deck (4 straps)

6. Remove the cover over the bandswitch turret assembly underneath the chassis.

7. IMPORTANT!!!  Before removing the RF deck, do one of the following:

Option A. Position the band switch 1/2 way between bands so no band switch coils are engaged in the fingers of the RF deck. I found this a little hard to gauge.

9. After the RF deck is out, you can replace the BBODs. They are obvious. There were a total of 22 on my RF deck, all .01mfds.  It would be advisable to check all resistors in the RF deck, leaky BBOD's will cause many of them to overheat and increase in value.  Now's the time to replace any that are more than about 10% from nominal value.