The last few months on the local CB channel have been the most fun for me since I moved to this area almost 7 years ago. There's been some clowning around, a little psychological chain-yankin' of some of the more abrasive people, lampooning of the local jargon, making some new friends, as well as rediscovering those old rigs that we ran (or only dreamed about) back in the heyday of CB radio some 30+ years ago. Ebay has been a wonderful source of old radios and with all the recent talk about our "Classic Radios", a few people have been bitten by the bug and have obtained some vintage 60's and 70's radios to play with. The fact that our current home channel is within the original 23 channel band plan makes it ideal for those old frequency challenged rigs to perform seamlessly, and in some cases better or at least with a little more warmth and character, alongside our more modern rigs. As I mentioned before, Ebay has been a virtual goldmine of old rigs to be had. But anytime you purchase something that's 25 years old or older, it becomes a crap shoot as to whether it will work properly or not when it finally arrives at your door. The standard Ebay seller disclaimer of: "I plugged it in and it lights up, but I don't know anything about radios, so I don't know if it works", pretty much reinforces the reality of this gamble. In some cases, a little cleaning and a quick alignment is all that the rig needs to be brought back to its original glory. In other cases, some more extensive work is required before the rig will be usable. Such is often the case with tube rigs. Tube rigs have been especially appealing to those of us hopelessly smitten by the allure of classic rig restoration, as these rigs seem to have the most nostalgic charm, and they have that unique audio quality which is more warm and room filling. But tube rigs are also normally the oldest radios (many are 40+ years old now), and some of their original parts may have failed (or are in the process of) from age. Fortunately, modern replacement parts are usually available and, in most cases, can be used as a substitute for the original parts, even if, in some cases, they are physically different from the original. But unless you are a true purist, this is normally not too much of a concern.
I have been fortunate in that I still have my original Lafayette Comstat 25, which I picked up as my very first full powered base station rig in late 1974 (the rig was already 9 years old then). This rig was used extensively for the first 2 years that I had it, not only for many hours of talking, but also as a platform for technical experimentation. It was a key part of my early radio experience. But eventually, as my station continued to evolve, the Lafayette found itself slowly being pushed to the back of the operating table. This first became evident shortly after I obtained my first base SSB rig, and then, as the 40 channel band plan became legal in 1977, when I slowly obtained more frequency capable radios. I did not appreciate the nostalgic appeal of tube rigs yet since, at that time, they were just old enough to be considered obsolete, but not old enough yet to be considered classic. Besides, the locals and I were all caught up in the "newfangled" PLL rigs and what they could be made to do and, in contrast, those old 23 channel crystal rigs seemed as primitive and out of touch with us as, well, CB radio seems to today's cell phone junkies. Ironically, it was this lack of perceived value that was likely responsible for my having kept the rig for all these years. Back in 1978, I was certainly not thinking about what I would be doing 28 years in the future, and of the renewed interest in these old vintage rigs. No, I kept it simply because I probably wouldn't have gotten more than around $10 if I had tried to sell it, and it had more sentimental worth to me than to simply throw away. In all likelihood, if someone had offered me $100 (or even $50) for it back then, I'd have probably sold it. But since that didn't happen, I ended up keeping the rig although, at that point, its primary residence had become a shelf in my closet, as the old rig no longer warranted a permanent spot on my operating table. Every once in a while, I would bring it down from the closet shelf, dust it off, and then operating it when I felt those first little pangs of nostalgia, or when I wanted to convince myself just how much "better" my more modern rigs were. I can remember thinking, during one such operating session: "How did I survive back then ("then" being only about 10 years prior at that point)?", being restricted to the AM-only, no-extra-frequency-capable Lafayette?" This was many years before my journey of retrospection and discovery where I came to realize that the conditions, which had made the CB experience the most fun for me, were created precisely because of my (and most of my friends) modest radio capability. In those early days, that Lafayette turned out to be a great platform for experimenting, and was very forgiving of my fledgling "hunt and peck" style of engineering, the results of which brought forth such crude projects as the "Poor Man's VFO", "The Poor Man's BFO", and other little projects. Like a Timex watch, the radio took a lickin' and kept on tickin'. Then, in the late 80's, my home channel moved beyond the capability of the Comstat to tune to, and so it sat on the closet shelf collecting dust for even longer. Eventually, by the mid to late 90's, when I found myself on Channel 29 (Which the Lafayette had an add-on crystal for) I decided to dust it off, fire it up and see if it still worked. This time when the rig was turned on, I was met with a cloud of smoke and the smell of a burned resistor. When I took the bottom cover off and started probing around, I discovered that a cap had shorted which placed line voltage across a resistor, and it had started smoking. I replaced the shorted cap, and fired the rig up again. This time the receiver seemed to come up but it had a howling noise in the speaker. The transmit also seemed to work, but I started smelling another burning resistor. This time the culprit was the plate dropping resistor for the transmit final tube. Some further investigation revealed that the final tube appeared to be taking off into oscillation during receive. I didn't have a schematic of this radio, and SAMS photofacts only covered the Comstat 25A and 25B models, which were significantly different. Without much in the way of a schematic, and really not that much incentive, the rig was put back together and returned to the shelf, with a "some day, I'll fix it" promise.
That "some day" didn't come about until June 2006, nearly 10 years later. I had moved to my new location, and the Comstat was once again taking up space on yet another closet shelf along with a growing collection of other classic rigs that I had been slowly acquiring over the last 10 years. Our local Channel 21 group was starting to play with classic rigs and I had brought down some of my own to play with. I started with my Hy-Gain 623, which had a tube final in it, but was otherwise solid state. I had also purchased a Royce 640 from EBay, and briefly ran my Cobra 135. But the big push was for all tube rigs and I wanted to get an all-tube rig to truly relive the classic era. Once again, my old trusty Lafayette came to the rescue. But before it could be used on the air again, it needed a little TLC first. The rig still had that nasty little oscillation problem, and who knows what other failures had occurred during the last 10 years of dust collecting. But now I had the incentive to do what I didn't want to be bothered with before. With concern for additional capacitor failures, I wisely chose to fire the rig up for the first time, by using a VARIAC variable voltage transformer, so as to not "shock" those old parts, with a huge inrush of current. Knowing that one of the biggest part failures to occur in these old tube rigs were paper and electrolytic capacitors, I started looking in that area. I figured a cap had opened in the final area, which then allowed the tube to oscillate. My first attempt to isolate the bad cap was unsuccessful. But I did prove for certain that the final was the part that was oscillating by removing the plate voltage from the tube, and observing that the parasitic oscillation (which, according to the spectrum analyzer, was around 267 MHz) stopped. There were only a couple of caps on the final, and replacing them didn't fix the problem. I was a bit discouraged to say the least. But then I got a lucky break. After 30 years of not being able to find a schematic of this rig, I managed to find one on-line at CBTricks.com. This is an absolutely fabulous web site for information on many old rigs, and accessories. With the aid of the schematic, I was able to determine that the final tube was missing its -82V bias voltage (a HA!). Turns out, there was an open coupling cap (I knew it had to be a cap) where the negative bias voltage was tapped off from the power supply secondary. Replacing the cap and restoring the bias voltage solved the oscillation problem and the rig was soon stable enough to consider operating. But even though the radio was now more or less working again, time had not been kind to this rig. In addition to the bad caps, two crystals were now totally dead, and most of the others were at least somewhat off-frequency. In typical Murphy fashion, the crystal with the worst drift had to be the main synthesizer crystal for channel 21 (And 22, 22"A" and "B", and 23). This crystal was a whopping 5 Khz low, and way too far off frequency to net back in. Heating the crystal with a soldering iron brought it back, but only until the heat was removed. Since I could not raise the crystal's frequency, the remaining quick and dirty solution was to drop the frequency an additional 5 Khz, for a total drop of 10 Khz. So while each channel in that group was now off by a whole channel, what was there would at least be on-frequency. So while the dial may say 22, I'm really on channel 21. A kludge for sure, but at least I'm where I want to be. The rig was then given a quick alignment. I removed the power mod that had been done to the rig before I had gotten it, which had resulted in a close to 6 watt carrier output, the transmitter was aligned for minimum spurious output, and the power set back to 3.5 watts.
So now for the moment of truth, it was time for the Lafayette to strut its stuff on the air for the first time in about 15 years. I plugged in the power and antenna connections, and turned the power switch on and waited for what seemed like forever for the tubes to warm up and come to life. Fortunately for me, the rig did not disappoint. The receiver was sensitive and receive audio was warm, although it seems to have a problem with the squelch not working (oh well, back to the bench). The transmit audio was strong and full, and seemed to gather a thumbs-up from the local group. I remember back in the old days that the transmit modulation, while generally ok, was somewhat bassy or muffled. I believe now that this was the result of the aforementioned power mod which, while it did boost carrier power, it did nothing for the audio drive, and actually reduced modulation percentage. Now that the power mod was removed, the audio cleaned up quite a bit. I felt a surge of pride in bringing this rig back from the dead or, at the very least, comatose. But it was even more rewarding, from a nostalgic standpoint, to be back in front of the very same rig that I had cut my radio teeth on over 35 years ago. The memorable sound of the relay "clunking", the familiar smell of the tubes, and the warm glow of the meter and channel indicator lights all brought back those vivid memories. At one point, I turned the lights out in my room, basked in the glow of the tubes, and watched the pattern of the lights projecting through the cover slots up on to the ceiling. It was a wonderfully familiar sight and for a brief moment it was 1975 again. You just can't put a price on that............
Update: The Lafayette was once again taken apart to get to the bottom of the squelch problem. Seems that the squelch would work when it was first turned on. But as the rig warmed up over the course of an hour or so, the control needed to be advanced further and further until it maxed out and no longer worked. Further investigation revealed that the -82V supply was gradually falling until it hit about -50V. Turns out that another cap was leaky and was dragging the voltage down. Replacing the cap cured the problem, and now the rig is once again fully functional (Except for some off-frequency crystals).Update 2013: Restoration continues for my prized Comstat. I recently discovered two nearly spent cathode bypass caps in the audio output and mic preamp sections. Replacing those has really woken up the transmit modulation. This radio NEVER sounded this good back in the 70's. I'm getting all sorts of good reports from it now. On the other hand, the radio has developed a new problem. Intermittent receiver dropping out. Not really completely out, but really weak. Interestingly, I can align one of the I.F. cans and usually bring it back to full sensitivity. Then it will drop out again, necessitating another alignment. At first I though it was a bad tube, but now I'm thinking that one of the internal capacitors in the I.F. can is becoming intermittent. Fortunately, I have a few junk Comstat 25A's that I can rob parts from. I'll have to try this next.