Just out of curiosity, what kind of color bar generator makes those annotated bars?

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Just out of curiosity, what kind of color bar generator makes those annotated bars?

I kinda wondered if someone might notice that. :) It's a B&K Television Analyst. It has a flying-spot scanner consisting of a small CRT (which glows with a odd-looking dim purple-ish light... its output isn't UV or something is it..?) with a phototube sensor set a few inches away. There's a holder mounted in front of the CRT for inserting tranparancies. The phototube sensor measures light from the CRT as the CRT scans a plain raster, thus generating a video signal based on whatever image is on the transparancy. These things originally came with several different transparancies, including various dot/line patterns and a version of the ever-popular "Indian Head" test pattern. While this sort of flying-spot scanner is only capable of producing B&W images (I'm not sure it can even make grey-scale images; I haven't tried that yet), most? all? TV Analysts have a built-in simple ungated rainbow generator, which if enabled and used with the appropriate "color bar" slide, makes for something that looks like a gated rainbow with nifty labels for the colors. :) Oh, and it also has a simple audio oscillator to provide a test tone on the sound carrier.

I've seen these TV Analysts show up at hamfests for years (usually at near-giveaway prices), but for whatever reason never bothered to pick one up until a couple of weeks ago. I wish I had earlier-- I never quite realized just how versitile it is! Not only can it generate arbitrary patterns on its scanner, but it can output them in a variety of ways-- either use its built-in modulator to produce RF (at any VHF channel-- later versions of the Analyst could even output on any UHF channel as well) or produce directly at IF frequencies (tunable over a wide range too!), or a plain detector-level video signal. It can even be used to provide substitute sync signals to a TV, or vertical and/or horizontal sweep signals. The video sweep rates are even adjustable over what appears to be a fairly wide range. I'm not sure (I don't have the manual, unfortunately), but I suspect it can even directly produce a substitute HV sweep (from an 'extra' horizontal output tube inside the Analyst) to a TV for troubleshooting purposes.

There appear to be a variety of other things this puppy can do, but without the manual, I'm not quite sure what they are. :)

I have one of those B&K TV Analyst. It has turned out to be a really handy tool in finding bad components. I have used mine on b&w sets. With a test pattern inserted, you start at the antenna terminal. If no picture there, move to the IF stages, If no picture there, you move to each following stage until you finally get a picture. Then, back track just a little and find the bad component. It's good to have for sets that have a hard to find problem.

If you don't want to replace every paper cap, you need to get a cap tester that will measure leakage under full voltage. Sencore made a number of models which work well for that. I can almost guarantee that you'll find out every paper cap is bad. Not totally recapping a 50's TV is like restoring a 50's car and leaving the original rubber hoses, belts and tires on it. Sure, you might be able to get away with it for a while, but it will be unreliable and won't perform as it was desgined to.

Yeah, I've got a couple of those capacitor testers (one Heathkit and one Knightkit), and I must say they're really handy, since, as you say, they can test for leakage at full voltage. I've encountered high-voltage caps before that test great at 25V, but that quickly deteriorate once you get the voltage up past 100V. Usually it's a reasonably quick and helpful tool. In this particular case, though, the "bad guy" cap in question tested just fine at the maximum test voltage, so I didn't figure it to be the culprit. I guess it's just another reminder that test equipment doesn't necessarily reflect actual circuit performance..! I've also got one of those Sprague 'Quick-Check' testers that can check caps for opens and shorts even while in circuit.

As for the recapping philosophy, I can understand your point, and I realize that you're not alone in your opinion, but on the other hand, I'm not entirely sold on the analogy. Belts, hoses, and tires were always intended to be "consumable" parts on a car (take a look at what's not covered on the warranty of a new car!). I think a (somewhat) better analogy to completely re-capping a 50's TV would be that of replacing the carburator and fuel system along with the distributor, alternator, the wiring, and the rest of the electrical system on a 50's car all with equivalent components from a more modern car regardless of the condition or functionality of the original components. Sure, you may save some time and end up with a more reliable car, but one look under the hood will make the more modern replacements stand out and appear out of place. It's really a trade off, and one that I realize can be rather touchy and has its proponents on both sides. (Sorry!) On the one hand, I like to keep my vintage electronics close to as "original" as practical, but on the other hand, I also don't go so far as disguising modern components inside old shells (though I certainly don't have a problem with those who do). Since this set isn't intended to be a "daily driver", and I'm not in a big rush to finish, I think it's reasonable to try to keep things as original as is practical and safe. [If I was planning to run this TV for several hours a day, I'd be more likely to agree with your sentiment, but since I'm not...] Also, I tend to be of the "if it ain't broke, don't fix it!" mindset. Besides, if I just went and replaced everything wholesale, I'd miss out on most of the whole "troubleshooting" part of the project, which can be an educational experience all in of itself, even if it is frustrating at times. :)

Anyway, feel free to disagree!

PS: The chroma section of this set has very few paper caps (most of them are ceramic discs), and I've already tried replacing two of the more suspicious paper caps anyway, so I tend not to think it's a paper cap at fault in this particular case.

Once you loose an irreplaceable power transformer in an early TV because of some "original" capacitor that you did not replace, you may change your mind!!! Personally, I would rather have a working set with some non-original caps than something that can only be a display item.

If it was built before 1960, I replace all paper and electrolytic caps. I tried leaving an original paper capacitor which had all of 4 volts on it in a 1953 Emerson that I restored. Sure enough the AGC began giving troubles and replacing this capacitor fixed it.

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This may be a little bit of a bone of contention for me but the equipment I mostly work with is in kind of a different situation.
We generally replace all paper and electrolytic caps and selenium diodes in tube type equipment...you will have problems crop up eventually with these old caps/rectifiers if you don't.

Some of our tube type equipment really still works hard for its living doing 12 hr. or more a day constant service such as our jukeboxes and PA amps...replacing all those old components keeps this industrial/commercial equipment performing like it ought to. We want to give the same kind of reliability to our clients when refurbishing old equipment so they can use it as much as they want without having to "baby" it.

The cost of caps is insignificant to just go ahead and recap the equipment completely while you have it disassembled on the bench as opposed to having call backs because of problems cropping up due to flaky old components. Much of the tube-type equipment we work on is not collectors items but units going back into a real "working life" so reliability is paramount.
Even if the equipment is only used occasionally, replacing old caps and rectifiers ensures that there will not be anymore degradation of the old parts causing more problems.

Wow, what an interesting and intriguing statement: “Much of the tube-type equipment we work on is not collectors items but units going back into a real "working life"....

Even 50-kW broadcast transmitters are solid-state today!

Perhaps, Chad, you can give us further insight into the use of tubes in today's society. Obviously the audio crowd takes a big slice of the tube pie (is this not AudioKarma after all), but what other – including commercial – uses of tubes are there today in your experience?

Some of the tube type products going back in to full time service that we have worked on include Hammond organs, Baldwin organs, jukeboxes (for home use), Gibson and other guitar amps, stereo amplifiers and receivers, and console stereos. These units are carrying on for the most part the service they started out with, however most tube type jukeboxes are no longer on coin routes but in private homes.

AM Antique radios and small phonographs tend to be items people use more for special occasions or for sentimental value as they don't seem to fit in to modern life in the way they once did. Have had only 2 tube type TV's come in for repair...it seems like most people have gotten rid of tube type sets but there are a few customers who still have them in addition to modern sets.

Chad use the salient word, "reliability". When I restore a 1940s B&W TV, or a 1950s color TV, I replace all the wax paper and electrolytic capacitors. I often test the wax paper caps as I remove them, and many of them show low leakage, and would work fine in many applications. But what I want most of all is to improve the reliability of the TV I am working on. If you leave the "good" wax paper and electrolytic caps in the set, it is cretin that you will be back in the set sooner than later hunting for the bad component.

Of course, replacing all these caps only improves your reliability so much. The set is still full of old parts, which have high failure rates due to the effects of time and use.

I have a couple of the B&K Analysts, the older one seems to have HV problems. The newer one doesn't seem to work right either but I haven't really played with it much. I should, since its been sitting there taking up a big chunk of my bench for a couple years now! I got it from the local TV/Appliance shop when the owner retired, it had been sitting on a shelf in the back room for so long that he didn't know what it was, and neither did I at first! Up on that shelf it looked like a high-end shortwave receiver!

In general, on anything from the 50s or older I replace all the caps I can. Some, in particular, are a real pain to take apart, so why have to do it twice? Changing caps can be fun, anyway. I haven't changed many caps on 60s sets, usually I wait for a problem to arise.

Going along with what Chad said, there are a number of tube organs around. I looked at one for my insurance agent awhile back (needs a motor) & our church organ is tube type. I use a tube amp for various Lions Club events (since some creep stole the solid state amp we used to have). Right now I am working on rigging up a second amp so we can call bingo plus make announcements out on the carnival grounds. The main amp I've used is a Muzak unit, 20 or 25 watts. I have a big, bad 75 watt Muzak that I bought for 50 cents (same price I paid for the smaller one!) but this one is missing all the tubes. When I started adding them up (all industrial types) I decided to shelve it. Now I'll try an old David Bogen unit that just needs the 6L6's. Anyway, from other forums I have read that there are quite a few radio stations still running tube equipment.

Of course, the goofy things I do (like with those amps) don't count, I'm the guy sitting here in the office listening to Benny Goodman on a '42 Airline that I fixed up for a friend.

Adding a line fuse and strategically-placed B+ and/or cathode-circuit fuses (pigtail fuses hidden under the chassis with clear heat shrink tubing slipped over them, for example) tends to minimize risk of catastrophic failures, even with some marginal capacitors left in place. What I typically do is add some safety features and as much preventive recapping as my clients are willing to pay for, which tends to vary somewhat. For items in my private collection, I add safety devices and perform needed repairs first, then recap as preventive maintenance as time permits. Some years ago, tubes were rated with TWO sets of ratings, designated "CCS" for "Continuous Commercial Service" and "ICAS" for "Intermittent Commercial/Amatuer Service" and many of the devices we AK members restore are actually transitioning from the continuous use for which they were initially designed to intermittent use.

Paper capacitors which show visible signs of "hot spots" (bubbles in their wax coating) and those which are responsible for crummy performance and/or out-of-spec readings during a check of tube pin voltages are the first ones I replace. Any significant change in the set's performance is a sign to me that it needs to be inspected more thoroughly at some point, and I've had good results with having adequate advance warning of performance issues. Anything from a sudden onset of touchy sync to a blown fuse will get a set in my collection tagged for a trip to the workbench at my earliest opportunity.

Adding a line fuse and strategically-placed B+ and/or cathode-circuit fuses (pigtail fuses hidden under the chassis with clear heat shrink tubing slipped over them, for example) tends to minimize risk of catastrophic failures, even with some marginal capacitors left in place. What I typically do is add some safety features and as much preventive recapping as my clients are willing to pay for, which tends to vary somewhat. For items in my private collection, I add safety devices and perform needed repairs first, then recap as preventive maintenance as time permits. Some years ago, tubes were rated with TWO sets of ratings, designated "CCS" for "Continuous Commercial Service" and "ICAS" for "Intermittent Commercial/Amatuer Service" and many of the devices we AK members restore are actually transitioning from the continuous use for which they were initially designed to intermittent use.

Paper capacitors which show visible signs of "hot spots" (bubbles in their wax coating) and those which are responsible for crummy performance and/or out-of-spec readings during a check of tube pin voltages are the first ones I replace. Any significant change in the set's performance is a sign to me that it needs to be inspected more thoroughly at some point, and I've had good results with having adequate advance warning of performance issues. Anything from a sudden onset of touchy sync to a blown fuse will get a set in my collection tagged for a trip to the workbench at my earliest opportunity.

What I typically do is add some safety features and as much preventive recapping as my clients are willing to pay for, which tends to vary somewhat. For items in my private collection, I add safety devices and perform needed repairs first, then recap as preventive maintenance as time permits.




John,

I have to disagree with you on both counts, except the safety issues. When I get a request for restoration on any piece of equipment, the first thing I tell the owner is that I will only do a "restoration", complete replacement of all caps, resistors that are more than 20% out of tolerance, and any piece that looks or smells like it has been over stressed. I won't do a "just make it play" repair, yes it is more expensive, but I really don't want to see the piece again. I can count on one hand the number of sets that have come back to be worked on again, and they are usually due to owner "issues", or because I didn't follow my own rules and decided to cut corners and leave a part in that "seemed" to be good. This is especially important with my customers who are dealers and are selling the set to the general public.

The items in my own collection get a full restoration when I have the set opened up the first time, again I don't want to go back into the set again.

As John F. pointed out there are many other parts in the set that can look, smell, or feel OK when you are doing the original work, but can and probably will fail at some point due to age and other issues that can't be controlled, i.e. #1 failure after the fact = tubes.

BTW, I have done a few restorations where everything except the transformers, coils, tube sockets, and parts unique to the set were replaced. Was it worth it? I really don't know, but the customer was happy (except maybe for the dent in his wallet) and I like to believe he has a set that works as good as new and it will continue to work that way for another 50-60 years.


Chuck

I only work on equipment that I own, as I do not have time for anything else. However, even with my equipment, I take Andy's and ChuckA's approach on any equipment made prior to 1960. Replace all paper and electrolytic caps!

I once left a paper cap in an TV agc circuit that had all of 4 volts on it. The TV it was in began to overload as if the AGC was not working properly. Guess what-it was that cap. I have also tried "Reforming" electronics as some have recommended only to have to replace them in a short time due to re-appearing power supply filtering hum, etc.

Trying to a few dollars by leaving old paper or electrolytic capacitors in place is not worth the hassle.

I will just chime in and agree with those who replace all paper and electrolytic caps.

All it takes is toasting one expensive power transformer (raises his hand -- yes, I did that), or having to haul a "restored" set back onto the workbench a second time (raises hand again).

As Chuck said, once I am done working on a set, I don't want to see it again for a long time. Other parts can and do fail, but not half as often as cruddy old caps that you leave in place.

Phil Nelson

Well , i am no pro at tv restoration . I mostly did radios for the longest time , but i just started getting into old tvs recently becuase it kinda interesting and fun . Anyway , as far as replacing capacitors , well i had a old magnavox that a friend of mine did a complete restoration on and basically , he recapped the whole tv and i must say it works fantastic . Its been going for 8 months now strong , with no problems or issues . It plays just as nice as it was when my parents bought it new in 1966 . So i have to say recapping a old tv seems to be the most practical thing to do . Capacitors are not expensive either . But thats my opinion .

Well , i must say i am not a expert at restoring old tvs . I actually just started repairing some of my own stuff . Up until a few months back , i mainly just fooled with radios . However , a friend of mine,last year , restored a magnavox color console my folks bought brand new back in 1966 . He recapped the whole set , replaced any bad resisters, tubes etc . And like i said i am not a expert but i use this tv on a regular basis and it never gives me any trouble whatsever , nor does it even seem to need adjusting. It plays like the day it came home from the store when it was new . So i could agree with the guys who say a old set should be recapped.

I strongly prefer to presume paper capacitors to be unreliable and replace them, however, limited bench space and an aversion to leaving open chassis strewn about the house and shop tends to cause me to "button up" some of my own gear and set it aside to focus on items that customers have sent. My own collection has well-hidden protective devices installed and re-formed electrolytics and each unit will be recapped as time and space permit. Electrolytics, however, are sealed units which can be tested reliably and any such units which can be re-formed to within the often-cited maximum leakage specification of 1/5(sqrt(C*V)) microamperes I prefer to leave in place rather than hanging modern electrolytics underneath the chassis when the original cans are working. I am, however, working on the development of an efficient way of re-stuffing the cans with modern capacitors so as to avoid the need for re-engineering sets to make room for modern electrolytics under the chassis. There are multiple considerations in developing this method, among them is providing terminal lugs on the bottom of the re-stuffed capacitor cans which have mechanical strength to allow them to be used as tie points for other components as was often done in the sets' original layouts. The first few cans I have opened by loosening the crimp along the circumference of their bases often suffer damage to the phenolic wafers which supported the terminal lugs during heating to loosen the insides of the units. I'm working on resolving this issue by practicing on a box of "junk" cans that I have saved.

My aversion to leaving sets open was especially strong when a former live-in girlfriend insisted on her four cats being allowed to have the run of the house and not be chastised for or deterred in any way from climbing on anything, including computer, audio, video, or any other electronics in the house. Aside from her refusing to work, contribute toward expenses, or to share household responsibilities as we had agreed, occasional damage to equipment and the impossibility of playing my extensive collection of vinyl without fear of the turntable being disturbed while operating were among the many reasons for my ending that relationship.

As an aside, my ex eventually did ease up on insisting that the cats not be chasised for climbing on electronic items after I told her of a technical support call to a satellite television service that I had heard about. According to the agent who took the call, it began with the customer stating that, until an hour ago, he HAD a satellite receiver and he HAD a cat. It seems the late feline made the fatal choice of "marking" the receiver as part of his territory, hitting the unit's AC power supply and thus electrocuting himself and blowing out the receiver. After I warned her of the risks to the cats' safety by their being allowed to climb on live electrical equipment, she decided that chastising them was better than risking that they might suffer the same fate as that satellite customer's unfortunate pet.

One of the cats hacked up a hairball on my workbench at one point. Fortunately, there was nothing sitting open on the bench at the time and no paperwork sitting out to possibly be destroyed. The carelessness of other family members and a sibling who once fired 6 or more shots from an air rifle into the laminated safety glass on a nice '68 Zenith B/W portable's 12" CRT taught me to not leave equipment out in the open. My "kid" brother and a friend of his were trying to see if they could get that CRT to implode while I was out on a date with one of a series of girlfriends during my teen years. Of course, beating the crap out of him for it wasn't an option. A few years later, when he asked me to "cover" for him while he cheated on a girlfriend of his, I got even by making sure he got caught. lol The "other woman" dumped him, and the "steady" girlfriend kept him on a short leash for a while. Didn't really do anything to get him caught other than a crummy job of discouraging the "steady" from showing up at the house while the other girl was there. Got even for that shot-up picture tube.

Electrolytics, however, are sealed units which can be tested reliably and any such units which can be re-formed to within the often-cited maximum leakage specification of 1/5(sqrt(C*V)) microamperes I prefer to leave in place rather than hanging modern electrolytics underneath the chassis when the original cans are working.I agree and get a warm fuzzy when the original electrolytics are doing their thing in a power supply (I tend to replace those used elsewhere), but the first time I grabbed a hot metal can tended to temper my opinion.

However, in my current operational CT-100 both the 200 uF, 250V doubler circuit electrolytics are still doing a fine job after 53 years :banana: . All the rest are new and hidden away, at least hidden away under the chassis. It's my compromise.

It's a shame that A.G. Tannenbaum doesn't have that massive list of NOS twist-lock and other electrolytics posted anymore. They were a great resource and the format of that list made it a fantastic reference tool. They even gladly exchanged any that I couldn't get to re-form to that 1/5(sqrt(C*V)) specification on all sections, and there was only ONE of the many I had bought from them that I ever needed to exchange. I almost went through a week of mourning over their site having done away with that list. Talk about an amazing Mallory/Sprague/CDE/WE cross-reference, that site was great and right on the Web. It was a huge disappointment to click the link in the Vendors subcategory of my Favorites and get a "Not Found" error.

As stated before, I have had very poor experience with "reformed" capacitors lasting. They had low hum just after re-forming, but it soon returned. For this reason (and to prevent expensive power transformers from being damaged), I always replace these.

I do leave the originals in place for cosmetic reasons in some cases. Disconnected, of course.

In a well-designed circuit, only about 2/3 to 3/4 of rated working voltage is actually applied across any electrolytic capacitor. With re-forming to the stated maximum leakage specification, actual operating DC leakage current will be far below maximum permissible. I have had excellent results, even with equipment which is kept in the less than ideal environment of my basement workshop. Variations in temperature and humidity are the main reason my 547 requires maintenance every 3 years and why I perform maintenance at 2 year intervals.

I provide additional overload protection to prevent marginal performance from becoming catastrophic chain-reactions, and I've seen far more cases where catastrophic failures resulted from well-meaning attempts to re-engineer component layouts to make components which did not meet one or more of the original selection criteria of the original part fit than from any other cause. As stated, though, I am working toward a solution to the shortcomings of restuffing cans. I have, however, had very good results with properly tested and re-formed original and/or NOS units. Being bitten by an unexpectedly "live" can often results in accidental damage to internal components due to involuntary recoil from the shock. This is yet another reason why I minimize re-engineering. I suppose a reasonable compromise when re-engineering would be to wrap all exposed cans with a single thickness of PVC tape to minimize shock hazard from a "floating" can.

I've worked on sets where a recoil from a shock had snapped tuning slugs and/or toppled and destroyed IF transformers. The all-time worst case of "permanent display piece" I have ever seen was, unfortunately, a very rare early color chassis whose owner had re-engineered one too many stages in the process of recapping (flyback toasted, IF transformers wrecked, severe instability in the few circuits that hadn't cooked). Failure to do a basic preliminary inspection is another catastrophe waiting to happen, as another unfortunate customer's listening test on a just-acquired vintage stereo receiver ended with a small fire under the power transformer, preventable had he merely checked to make sure that the fuseholder on the rear panel had not been bypassed before powering up. That unit was eventually restored to working order, but not without a costly transformer transplant.

Not at all advocating the careless handling of "unobtainium" here, merely pointing out that selection criteria other than just capacitance, working voltage, and leakage current are involved and there are potential trade-offs involved in re-engineering which require some careful consideration. Your mileage may vary.

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Regarding ESR testing, the actual test is accomplished by applying a low amplitude AC signal across the capacitor under test and measuring amplitude across the capacitor. Expensive ESR testers use a sinewave signal, but squarewave will also work. Here is a link to a DIY test adaptor for checking ESR with a scope or a DMM with an AC 200mV or 300mV range available. http://octopus.freeyellow.com/99.html. The circuit is simple and powered by an ordinary 9V battery. The author begins with a simplified version based on a hex inverter I.C. and does an excellent job of explaining the operating principle and the limitations of the simplified version before going on to provide a schematic, parts list, description, and operating instructions for the improved final version. By using a dual trace scope and applying the direct output to the other input, direct comparison of the two waveforms on the scope screen is possible. Paper capacitors should be replaced ASAP when restoring a vintage set to working order, but electrolytics with sufficiently low ESR, low leakage, and capacitance within factory-specified tolerance may be left in place once properly tested and re-formed and will thus minimize the need for re-engineering and the potential danger of replacing a superior part which has survived 50 or more years with a modern part whose reliability may be questionable due to cheap construction.

I will be constructing one of these for evaluation and will post my findings here.

Doesn't the fact that the vast majority of these sets that have been spared from ending up in landfills can be brought back to life once they find their way into the hands of those such as ourselves who care enough about preserving them to make the effort factor into the reason why we love them so much? Restoration would not be possible at all had the vast majority of these sets not been so well-enginnered and well-constructed in the first place.

"Time Capsules" were one of those 70s phenomena that I seem to remember, where items from the era were stored away to be reopened decades later. I challenge someone with the means to do so to arrange for a suitable restored and known-working vintage set, metered Variac, sealed bag of new "Orange Drop" caps, restored B&K TV Analyst, modern cheapie TV, DVD player, test pattern DVD, service literature and instructions to be sealed away to be reopened in perhaps 50 years just to see which set still works.

I don't think the ESR meter we have was too expensive...it's nice to have a factory made pre-calibrated unit. It has really proved useful especially in solid state equipment.

I don't understand the reluctance to replace old electrolytics. Reforming is a gamble at best. New electrolytics don't cost much, certainly much less than a new power transformer. As the old cap would say, "replace me now or replace me later (and maybe along with some other component I took out)". If you can't stand the look of new caps under the chassis, then re-stuff the cans.

I do not understand the reluctance either. I am just now working on a 1967 Motorola B&W TV, a hybrid set. I replaced a resistor in the AGC section and the set began working. However, I noticed after one hour of playing time, the horizontal would begin shrinking. I checked and the low voltage supply was falling. Then I noticed the filter cap was ever so slightly warm.

Replaced filters-problem fixed. Another example of what these old electrolytics will do if not replaced. Other caps are mylar, etc. These are still in the set.

I just purchashed one of those B&K analyst units . I am kinda new to tv repairs however i must say its a really nice piece of equipment and it has a lot of functions. Mine its pretty much all original with all test leads and original manuel . Its appears to have all original electrolytic caps still inside . Should i change them ???? I cant wait to learn how to use this . I have seen these unit but never had one before .

ESR testing and the inclusion of AC line, B+, and sweep circuit overload protection goes a long way and will prevent an unforeseen capacitor failure from resulting in chain-reaction damage such as power transformer meltdown.

Moving the B+ lead from its original connection on the rectifier tube socket (pin 8 on the 5U4 in RCA 721TS, for example) to an unused pin which a tube manual does not warn against using as a tie point (pin 1 in the 721TS example), I then join the "old" and "new" tie points with an appropriately sized PicoFuse. I use 500mA fast-acting in sets with a single 5U4 and 1A fast-acting in dual 5U4 sets. The design rule is a fast-acting fuse should be rated at 200% of normal operating current or a slo-blo fuse rated 125%. The 721TS transformer is rated to deliver 240mA, and 500mA is the closest available standard size. A 300mA slo-blo will also work.

Sweep circuts, I install a 250mA fast-acting PicoFuse in the damper cathode circuit by the same method as with a 5U4.

For AC line protection, I use a depth-limited drill to carefully remove one of the rivets holding the interlock connector in place. Using a Pop rivet gun, I re-attach the interlock with an AES p/n P-0100H terminal strip fastened under the new rivet, move one AC input lead to the new terminal, and calculate the appropriate fuse ratings based on the set's AC input current specification.

Electrolytics with unacceptable ESR, leakage, etc. are of course replaced, but properly-functioning units are left in place.

My ESR meter (Tenma) uses a 50kHz test frequency. I also have a Sprague TO-4 (original 12uF filters show low ESR and are still in place) with all paper capacitors replaced. The two critical bridge capacitors consist of matched pairs selected for +/-2% accuracy. A thoroughly-tested electrolytic stll reading low ESR, low leakage, and capacitance well within tolerance after 50+ years does not need to be replaced. If it does fail eventually, in a properly-inspected and serviced set, fuses will protect the major components and a subsequent ESR test will detect the failure.