RESTORING YOUR VINTAGE RADIO

Discussion in '"Boat Anchor" & Classic Equipment' started by KL7AJ, Apr 2, 2010.

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  1. KL7AJ

    KL7AJ Ham Member QRZ Page

    RESTORING YOUR VINTAGE RADIO

    By

    Bo Tanker



    It’s really exciting to see the renewed interest in classic, vintage, antique, and downright ancient amateur radio equipment. It’s really a great way of getting started in amateur radio for a number of reasons. And it’s nowhere near as daunting as some people believe.
    You can really learn some radio by using, restoring, or (horrors) even modifying a boat anchor. The parts inside are big, easily accessible, and readily identifiable. There are a lot fewer of them compared to a modern radio, and they are all replaceable. Things actually move inside boat anchors, so you can actually see how radio works.
    By the way, I should mention at this point that it seems a lot of the uninitiated refer to ANY amateur radio that happens to contain a tube or two a boat anchor. Excuse me, but a Yaesu FT-101 doesn’t even REMOTELY qualify as a boat anchor. It’s got a HANDLE on the thing, for crying out loud!
    If you can pick the rig up with one hand, it is NOT a boat anchor. If it has a transmitter AND a receiver in the same box, it’s PROBABLY not a boat anchor. One possible exception to this MIGHT be a 1970 Signal One. In fact, if it’s made in Japan, it’s CERTAINLY not a boat anchor, with the exception of some very early JRC radios.
    Even some venerable radios like the Drake Twins are only borderline boat anchors.
    Here’s a test for whether your radio qualifies as a boat anchor. First, locate your nearest ocean or Great Lake. (If you live in Nebraska, this may be a bit of a trick in itself). Go down to the nearest dock on the shore of the aforementioned ocean or Great Lake. Find a big boat. Look for a big, rusty pointy object dangling from a chain somewhere on that big boat. Pick up that big rusty pointy object dangling from the chain. Record or otherwise document the grunting sounds you make when you pick up that big pointy rusty object. Or, alternatively, record the pain level in your back as you pick up that big pointy rusty object.
    Now go home, pick up your radio, and compare your grunting and/or pain level with that experienced upon lifting the rusty pointy object dangling from the chain on the big boat.
    Is it comparable? If so, you might have a genuine boat anchor.
    Here are some names of some actual boat anchor manufacturers, in no particular order:

    National Radio
    Hammarlund
    Hallicrafters
    Collins
    Gonset
    Clegg
    Johnson
    Harvey Wells
    RME
    World Radio Labs
    Ameco
    JRC
    Drake
    Swan
    Central Electronics
    Heathkit
    TMC (Technical Materiel Corporation)
    Green or Black radios (Highly standardized radios made for the Army or Army Air Forces (USAAF) by various contractors, such as the “ARC” or “BC,” or “PRC” series of radios)
    Gray radios (Navy mil-spec radios. Similar to Green and Black radios, but generally easier to identify the actual manufacturer. The Hammarlund SP-600J was typical of this, with Hammarlund ID plate generally right on the front panel.
    Moseley
    Barker and Williamson (Best kept secret in all of “Boat Anchordom” Almost unheard of in their own time, but world class design and construction all around. A B&W radio is real find)

    I’ve certainly missed a few, but those are some names to look for.
    Now, here’s the good news and the bad news. First, the bad news: Ebay.
    About 20 years ago, I picked up my semi-mint condition Central Electronics 100V from a Silent Key estate sale. I paid $60 for the thing. I recently saw the same rig on Ebay, in nowhere NEAR as good a condition as mine…listed for $6500.
    It sold.
    There are actually a few morals to this story. The first is obvious: There’s a sucker born every minute. Now the 100V is a FINE radio...in fact, it’s by far my “favoritest” radio on the planet. But it was also my “favoritest” radio on the planet in 1990 when I bought it. Even so, I don’t think I would have paid more than $100 for it back then, and I certainly wouldn’t pay $6500 for it now!
    The other moral to the story is that most boat anchors AREN’T on Ebay. In fact, a good boat anchor is STILL the cheapest way to get on the air. I have a whole shack full of nice boat anchors, and most of them I didn’t pay a DIME for! The fact is, there are untold thousands of these radios that hams and non-hams alike just want to get rid of. I’ve been on BOTH sides of this equation for my entire ham “career.” I can’t remember how many of these I’ve given away...or how many have been given to me.
    The bottom line here is that, if you really want a boat anchor, you can get one. It may not be THE boat anchor, right off the bat. But it will be a boat anchor. Don’t be picky...until you really know what you want. Until then, learn to want what you have!

    Moving Right Along

    Well, with that out of the way, let’s assume you have a boat anchor of some sort and you want to make it work at least as well as it did when it was new. Actually, in most cases, it’s possible to make it work BETTER than when it was new!
    As far as COSMETIC restoration is concerned, that’s a very specialized art. Unless you’re HIGHLY skilled, it’s best to find one of these geniuses to do this for you. There are a few people out there that LOVE doing this stuff, and in my book, they’re right up with Rembrandt or Vermeer. Fortunately, I’ve been generally content to settle for Bob Ross.*
    In this article, I’ll be describing the EASY part of boat anchor restoration...the electronics.

    They’re all the Same

    Well, almost. There are some things common to almost all boat anchors that need the same attention. Some of this will be merely opinion, but experienced opinion, nevertheless.
    The number one problem with boat anchors is electrolytic capacitors. However, it ISN’T just boat anchors that suffer this malady. I have a friend who made a lot of good money during the late 1980s at a satellite TV installation and repair shop. He said his job title was “Electrolytic Capacitor Changer.” Fully 80% of his income was directly the result of changing electrolytic capacitors in satellite receivers.
    Now, notice that I specifically mentioned electrolytic capacitors. I have a 1926 Atwater Kent A.M. receiver that has the original silver mica capacitors in it. They work as good as the day they were made. In fact, in my entire ham career, I have NEVER seen a silver mica capacitor go bad. Which brings us to the next topic.


    The Radical Capacitectomy

    It used to be pretty standard practice with boat anchor restoration to instinctively perform a radical capacitectomy. Just replace every capacitor in the radio before even powering it up. This procedure probably never hurt anything. I used to do it all the time, myself. I’ve just learned that it isn’t often necessary. You used to be able to pick up a pile of Orange Drop capacitors from Radio Shack for a buck or so, so it wasn’t a big deal to do the radical surgery. In fact, if your rig has been fitted with Orange Drops (or “prune drops”…the maroon equivalents) it’s quite likely you’ll never have to change a capacitor again. These really are great capacitors. So, I’m not going to discourage you from doing this TOO much. But if you’re inherently lazy like me, there’s a better way.

    No Guts, No Glory

    Much to the horror of many of my fellow boatanchorologists, I have NEVER used a Variac to power up a boat anchor. The concept of using a Variac is to bring up the voltage of the radio SLOWLY, so if there are any bad capacitors, you won’t torch anything. Again, this is a procedure that probably won’t HURT anything, but it’s a bit of overkill, I think.
    If your boat anchor has a vacuum tube RECTIFIER in it, you already have the functional equivalent of a Variac in line….it takes a while to warm up before it can supply any current. If you have a bad filter capacitor in your power supply, the plates of your rectifier will probably glow red before you do any damage. In fact the only time I ever did any serious damage to a boat anchor with the sudden application of line voltage was a rig that someone had “improved” by replacing the vacuum tube rectifier with a couple of solid state diodes! This took out the power transformer of an only marginally valuable Hallicrafters S-40. Nevertheless, it was the first time I ever deigned to REWIND a transformer by myself. It was a lot of work, but it actually came out fine! The moral here is that, if someone WOUND the transformer in the first place, someone can probably REWIND it, as well. Like everything else good in life…it’s just a matter of time and patience. (However, in case you DO ever successfully rewind a power transformer, just don’t TELL anyone...you’ll never get a moment’s rest! Personal experience speaking here).


    The Hum Test

    One of the best quickie tests you can do on a boat anchor is the hum test. First, remove the rectifier tube. (If someone has done you the “favor” of replacing the rectifier with silicon diodes, UNDO the favor before you do anything else). If it’s a TRANSMITTER, remove the finals and the driver tube as well. Turn on the rig and LISTEN for the hum. This is your baseline hum level. All rigs will have some…if there’s a transformer at all. Remember that sound. Now, turn off the rig, and reinstall the rectifier tube. Turn it back on again. As the rectifier warms up, if you hear any sudden increase in hum level, you MAY have a bad filter cap. If things seem quiet, you’re probably good to go. If it’s a transmitter, shut it down, SHORT OUT any supply lines and filter caps with your shorting stick (you DO have a shorting stick, don’t you?) and replace the final or finals, and driver tube. Fire it up again, and listen for the hum. A serious overload with a boat anchor just SOUNDS ominous, menacing and nasty...you usually KNOW if there’s a problem. More often than not, however, there will be no problem.

    Tooby Tooby Too

    I collect tube testers just because I like tube testers, but if you’re a normal sort of human being you probably only need one. But you do need one. But you also need to know what they really tell you. Some of this comes with nothing but experience. For example, most tube testers don’t pull enough current to test a rectifier tube fully. They’ll tell you about leakage and shorts and emission just fine, but don’t expect to get a real meaningful current capacity reading on a 5U4! The best place to test this tube is IN THE TRANSMITTER! The same is the case with many receiving tubes. There’s probably no conceivable advantage in using receiving tubes with known inter-element leakage, but it can be AMAZING how well some old receivers will work with almost non-existent EMISSION. When tubes were DIRT CHEAP, I used to always do a TUBAL ligation (a “Valve Job” for our English brethren)…pull every tube out of a boat anchor, test them all on a tube tester, and chuck every one that didn’t have emission in the “green” area. This would be a HUGE mistake today! It’s amazing how well a “bad” tube can work in some receivers. This depends a great deal on the receiver design. For example, Collins receivers generally had TONS more available I.F. gain than they needed; using lots of moderate-gain stages with AGC feedback. If you had a “lazy” tube in the I.F. chain, you’d never know the difference. On the other hand, some inexpensive radios, particularly those using pentagrid converters are particularly susceptible to tube condition. Receivers that just “die” on certain spots on the dial are usually running their oscillator tubes right on the brink, and any significant loss of emission will cause them to stop oscillating.

    Gimme Mho

    You really want a tube tester that will measure mutual conductance. Mutual conductance is measured in “micromhos.” A mho is the unit of conductance, which is the reciprocal of resistance, and mho is ohm spelled backwards. Nowadays, the term mho has been replaced with the Siemens, because someone decided all electrical units have to be named after dead electrical dudes. But mho is better, because it’s easier to remember that with mo’ mho you have mo’ current flow. So mho is mo’ better.
    Most tube testers built after about 1940 can measure mutual conductance anyway, so it’s probably not a big deal to find one that fills the bill…but check it out anyway. Mutual conductance is a measurement of the GAIN of the tube, and is really a better indicator of how the thing is going to work (at least in receiving applications) than emission alone. Now, the savvy amongst us will wonder, “Isn’t the mutual conductance a function of the physical GEOMETRY inside the tube? How can that change just because the tube is old?”
    Good question! As it turns out, the mutual conductance of a tube will NOT change until the tube is essentially DEAD! In other words, mutual conductance is a far more GENEROUS measurement than emission. If you are showing nominal mutual conductance, you basically have a functioning tube! It takes VERY little current (determined by emission) for a tube to amplify voltage.
    Bottom line. An “emission only” tube tester makes you throw tubes away. A mutual conductance tube tester lets you keep them another day.
    Where emission IS important is in TRANSMITTING tubes, where you need to supply considerable current from the filament. Power drops off nearly directly with filament emission.

    Holy Scroll

    Most semi-modern tube testers have a built-in scroll showing every available tube type and the associated test settings, in a convenient alternative to the previous regime of carrying around a book that was always getting lost. The font of all human wisdom was contained in that scroll. If you had a particular tube that wasn’t written in the ham’s book of life, you were pretty much out of luck.
    Well, not entirely. If you have a venerable RCA tube manual, you can usually wing it. Just be sure your tube tester is set for the right pinout of your tube, and set the grid and filament to match the specs in the tube manual. I’ve done this with countless mil-spec type tubes with all kinds of oddball designations, even without the RCA Rosetta Stone. You get to where you can squint at the innards of a tube and figure out pretty much how it’s wired up, and what it’s supposed to do.

    In the O.R.

    We should probably remind you that most boat anchors have potentially lethal voltages in their torsos. It’s much preferable to having your rig on life support than having your BODY on life support. Though most of us “seasoned” boatachorologists have been knocked on our collective keisters a time or two, and actually require a therapeutic jolt once in a while, many others do NOT relish the potential (pun intended) of this experience.
    Have a shorting stick handy. ALWAYS use this to discharge any power supply capacitors. Be careful of any HIDDEN capacitors as well! Some rigs are notorious for harboring “gotcha” capacitors in unlikely places.
    Always measure high voltages with your RIGHT hand with your LEFT hand in your pocket….even if you’re left handed. Why? There’s a big artery that runs from your left arm right to your heart, that’s why. An artery basically filled with saltwater (unless you have a zero sodium diet), which is a pretty good conductor. I violated this rule once, working on a high powered transmitter at HIPAS Observatory. I got a hand-to-hand shock from a 900 volt bias supply…the worst path for a shock you can get. I had dutifully shorted out the plate voltage (17KV) like a good boy before working on the wee beastie. But I was unaware that the bias supply was activated whenever the filaments were on.
    As a result of this “tingle” I stuttered for three days. This is essentially the same voltage you’d encounter in a ham transmitter with a pair of 6146 tubes….a very common item in countless ham rigs.
    Don’t be scared; just be alert. America needs more lerts.


    Last things First


    Making a boat anchor work is the easy part. Making it work well can be something else. This is where we come to that thrilling procedure known as alignment. Like any good medical procedure, the radio alignment starts at the rump end and works up. Here’s the basic flow chart of a full alignment of a FUNCTIONAL single conversion general coverage receiver. We’ll discuss each step in detail, with some known quirks, and then touch on multiple conversion receivers in the next installment.

    1) Check functioning of audio output stage.
    2) Check audio driver stage
    3) Check the detector, and BFO (if one exists)
    4) Check i.f. alignment
    5) Check converter or local oscillator across ENTIRE frequency range.
    6) Dial tracking and alignment


    Let’s start with step 1, the audio output stage. Turn on your radio, let it warm up. Enjoy the pretty orange glow of the tubes. Inhale the fragrance of the hot wax on the capacitors (if you haven’t replaced them with newfangled orange drops). Spin the tuning dial or dials from end to end; be sure the dial cords are working as expected. Rotate every knob and switch through its entire range, listening for any unexpected crackles or crunches. Wobble each tube in its socket; there should be no oddball hisses or crunches. Now tune into a local A.M. station or strong shortwave broadcast station. Turn OFF the BFO. Turn ON the AGC. Turn the R.F. gain up full. Listen to the audio quality. If it sounds like a radio, it probably is. Turn OFF the AGC. The volume should increase noticeably. Don’t worry about distortion with AGC off. Turn AGC back on. If there’s a noise limiter (ANL) turn it on. You should hear considerable distortion on a strong station, but less on a weaker one. Turn the noise limiter off.
    At this point, we’ve actually verified steps 1 and 2, since the ANL is generally in the audio driver section.
    Now, for step 3. Tune the main tuning to a blank spot. Turn ON the BFO. You should hear a definite change in the background hiss. Now rotate the BFO through its range. The noise should decrease in pitch toward the center of the BFO and rise in pitch equally on both sides. If the noise is NOT lowest pitch in the center of the BFO rotation, you will have to align the BFO oscillator. On a rig like an S-40, you merely remove the knob, and turn the screw inside until the noise is “centered” and then replace the knob at the 12 o’clock position. Most simple rigs have a similar twiddlemethodology.
    For step 4, you will need an actual signal generator of some sort. Beg, borrow, steal, or make a 455KHz oscillator. This needs to be MODULATED with an audio tone, typically 400 Hz.
    Inject a weak 455 KC modulated signal into the last i.f. amplifier grid, using a 10 pf capacitor. You should hear the audio tone in the speaker. You want the audio level very low. Why? Because the human ear has a built-in speech compressor. It’s much EASIER to detect changes in level right at the threshold of hearing than it is at high volumes. Now, with an insulated twiddle stick, adjust both the upper and lower slugs of the last I.F. transformer for the loudest signal.
    Move the signal generator to the grid of the previous stage, which quite likely will be the mixer stage…but not necessarily. Reduce the signal generator level until the audio tone is right at the threshold of hearing. Adjust the upper and lower slugs of the FIRST i.f. transformer for maximum audio. It is this I.F. alignment that primarily determines the overall performance of your receiver, so it’s worth doing it right.
    Now for step 5. Remove the signal generator. Now tune the main tuning dial from end to end of EACH band. See that you hear the normal background hiss at all times (or preferably distant stations!) If the radio goes DEAD at any point, some attention is needed. You may need a new mixer or converter tube. SOMETIMES an oscillator alignment will cure this, but don’t count on it. If your receiver is alive everywhere, we can proceed to step 6.
    Step 6. The FUN part. (NOT!!!!)
    The purpose of the “front end” alignment is twofold. The first is to make the tuning dial track with reality (oscillator alignment). The second (R.F. alignment) is to optimize sensitivity and image rejection (as far as is possible with a single conversion receiver).
    The oscillator alignment is more of a pain than the R.F. alignment, but is well worth doing. To do this, you will need some known frequencies, near the top and bottom end of each band.

    MUY MUY IMPORTANTE!!!

    It is CRUCIAL that you perform the alignment on the highest frequency band first, and then work your way downward. If you fail to do this, you will find yourself in “alignment purgatory” for all eternity, a reiterative closed loop of interacting adjustments from which there is no escape. Well, unless you start over and do it right.
    Now, there are two adjustments for each band, one called “padding” and one called “trimming”. The PADDING capacitor, which is in PARALLEL with the main tuning capacitor sets the MINIMUM capacitance possible (separately for each band). The TRIMMING capacitor, which is in SERIES with the Padding/main tuning capacitor combo, sets the MAXIMUM capacitance possible (again, for each band). The RATIO between the trimmer and padder capacitors determines how much RANGE the main tuning has. Now, it may seem that we’re doing some of this alignment BACKWARDS, i.e. using the PADDING capacitor to set the alignment at the TOP of the dial, and the TRIMMER for the bottom end, but with a little thought (actually a whole LOT of thought!) you’ll eventually see how this works. In the meantime, you’ll just have to TRUST ME! (Scary words, no?)
    So, let’s start on the highest frequency band. (There seems to be no standard “numbering” system for bands. Band 1 could be the highest OR the lowest frequency band number. Just be aware of this)
    Tune the radio to a KNOWN frequency signal near the top of the dial. The CLOSER to the actual top end of the dial, the better. Set the main tuning so that it reads what it’s supposed to read for the station in question. Now, adjust the PADDER capacitor for maximum strength of that station. Now locate a station (or signal generator) near the BOTTOM of the band. Tune the main tuning to the correct indicated frequency. Now adjust the TRIMMER for the strongest signal. Now go BACK to the top end of the dial and check the PADDER capacitor again. You may have to “walk” back and forth a few times, since these two adjustments will interact. When the top band seems to track across the band, you’re good to go.
    Lather, rinse and repeat the process for the remaining bands, working progressively downwards. Be extremely careful NOT to inadvertently tweak any of the capacitors you’ve already properly adjusted. (Not that I ever would have done such a thing!)
    Now…after your padding and trimming has been accomplished for each band, all that’s left is the R.F. alignment. This is generally MUCH easier to do, because it generally only involves ONE twiddle for each band, normally just a padder. Find a station near the MIDDLE of each band, again beginning at the HIGHEST frequency band. Adjust the padder for the STRONGEST signal at that point. AGAIN, be VERY CAREFUL not to accidentally tweak your painstakingly adjusted OSCILLATOR alignments!
    Lather, rinse and repeat for the center of each remaining band.
    You are now done! You should have a NEW receiver!



    In the next installment, we’ll deal with multiple conversion receivers, notch filters, the magical mystery “XTAL PHASING” adjustment, passband tuning, and other niceties. Pretty much the same as the above procedure, just more of it.























    *Famous but dead drive-by oil painter from my home town of North Pole, Alaska
     
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  2. AF6LJ

    AF6LJ Ham Member QRZ Page

    Good Stuff.
    Having had a few old boat anchors I miss the smell of of one that has been on for most of a day.

    You really know you have a boat anchor if it has no electrolytics in it. I owned once and let it slip through my hands.. .
     
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  3. W3JN

    W3JN Ham Member QRZ Page

    Lots of good advice here, however.....

    Generally it's not true that receivers have both padders and trimmers, except perhaps at the lowest band. Every receiver I've been in (hundreds!) has had a trimmer for the high end, and a slug-tuned inductor (or in the case of some Nationals, an adjustable link inside the coil) for the low end, or no adjustment at all at the low end. Padders are rare indeed and the only place I've seen them is on the AM BCB, or lower.

    The author of this article is extremely lucky then. I've replaced dozens and dozens. Including every silver mica inside the IF transformers on a SX-42.

    Not really. The concept of using a variac to bring the radio up slowly (over the course of hours) is to let the electrolytic capacitors re-form. Still, with 60 year old components it's best to assume they are (or will soon be) bad. I ruined the power transformer on a rare SX-15 by not following my own advice.
     
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  4. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    Several things:

    The best tube checker in the world is the unit itself! Tubes that check fine in the "tester" don't always work well in the unit and, conversely, tubes that check bad in the "tester" often work fine in the unit. There was only one tube checker that was ever built which could really test tubes under actual operating conditions. This was built by General Electric back in the 1950s and it cost around $3 million in actual dollars at the time. Frankly, I own several tube checkers (including one built during the 1930s) and it has been years since I have even applied AC to any of them. I have been restoring / repairing "boat anchor" equipment for decades.

    Silver mica capacitors are now starting to go bad in high quantities. It seems that between 50 years and 60 years is their basic life span. Also, there are numerous fixed capacitors which appear to be mica but which are actually paper capacitors. These are called "micamold" capacitors and those need to be replaced immediately because the vast majority of those capacitors are definitely "leaky".

    I NEVER use a variac to slowly "bring up" any unit. As was pointed out by JN the primary purpose of this is to "reform" electrolytic capacitors and, unfortunately, even if you are able to "reform" the capacitors there is a very good chance that they won't last that long anyway. Now if the unit has been in regular use then even electrolytic capacitors from the 1920s and 1930s are still good. But, if the unit has not had voltage applied for a number of years then there is a VERY good chance that they have gone bad. Now there is an exception to this in the electrolytic capacitors used in the late 1920s and throughout the 1930s that have an actual liquid electrolytic solution rather than the paste type. If the liquid is still present (it will be unless the capacitor has developed a physical leak) then that type of capacitor will still be good.

    Orange Drops are only one of several brands of Polypropylene capacitors which are available today. Unfortunately, Vishay-Sprague, manufacturer of the Orange Drop capacitors, have gotten pretty greedy over the years and therefore Orange Drops are now relatively expensive. There are other brands of Polypropylene capacitors that work just as well and that are MUCH cheaper.

    If you don't replace the paper capacitors (wax, plastic enclosed like the Sprague "Black Beauty capacitors, micamolds, etc.) then you are definitely playing with dynamite. Those capacitors actually go bad when brand new, never been installed, sitting in a box on the shelf. Well over 95 percent of that type of capacitor ARE going to be leaky and the rest will soon become leaky when the set is in operation. When one of those capacitors becomes "leaky enough" it WILL basically "short out" and will often take things like i.f. transformers, tubes, and in the worst case the power transformer with it.

    Although paper capacitors were often used in every stage of "boat anchor" equipment most of those do NOT have to be replaced with "poly" type capacitors. Disc ceramic capacitors are considerably cheaper than other types and disc ceramic capacitors actually do a better job of bypassing. However, in audio stages, for coupling capacitors, the "poly" type of capacitors are preferred because, in most people's opinion, they do produce a better quality "sound". Also, when disc ceramic capacitors are used for audio coupling sometimes they actually become microphonic and you can actually hear audio from those capacitors.

    One thing that can happen, especially in units made during the 1930s, is that a stage may have problems after replacing the paper capacitors. This is usually caused by the fact that the original design actually relied on some leakage through the capacitor and the new capacitor basically does not have any leakage. In those cases adding a resistor between 470K ohms and 1 megohms across the capacitor will again allow the stage to work. Now the designer of the radio probably did not know that the leakage was necessary for the stage to work properly.

    As for solid-state rectifiers: I generally concur with the principle that the original tube-type rectifiers should be restored. However, there are exceptions to this rule especially in certain models of radios in which there is a problematic power transformer. This is especially true of the Hallicrafters HT-37 and the HT-32 series transmitters. The power transformers of those units are operating on the "ragged edge" and removing the tube rectifiers removes not only the power required by the filaments of the rectifier tubes but also, if properly done, removes the rectified high voltage from the transformer as well. Doing this can make the difference between years of operating and having the power transformer fail in a very short period of time.

    Especially in National receivers there is often a paper 1600 volt capacitor across the high voltage secondary of the power transformer. This needs to be immediately removed. Not even people who worked for National have any idea as to why this capacitor was installed and when (not if, but when) it fails it will take the power transformer with it!

    As for hum: If you use a pair of "modern" 8 ohm headphones in a "boat anchor" receiver you WILL hear hum no matter what you do. They were made to use high impedance headphones (i.e. 2000 ohms impedance or greater). If you use the proper headphones there will be very little, if any, hum.

    Getting back to capacitors: Although you might think that the unit is performing well without replacing the paper capacitors when you actually get around to replacing them the difference is performance is like "night and day". In well over 99 percent of the cases when the leaky capacitors are replace the performance will increase dramatically.

    Glen, K9STH
     
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  5. KL7AJ

    KL7AJ Ham Member QRZ Page

    Hi Glen:
    Thanks for the additional info. I agree that the radio itself is the best tube tester.
    As far as some designs relying on capacitor leakage for their operation...I think it's more likely they rely on parasitic INDUCTANCE. I have a friend that replaced all the i.f. transformers in a rig with newfangled low-inductance capacitors and they REFUSED to tune! So, one more quirk to look out for!

    ::)

    Eric
     
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  6. KA0SOG

    KA0SOG XML Subscriber QRZ Page

    My Personal Favorite is my Wireless 19 Set

    I love the smell of ozone in the morning.
     
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  7. KF7AYS

    KF7AYS Ham Member QRZ Page

    Great article. Thanks.
     
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  8. WA7PRC

    WA7PRC Ham Member QRZ Page

    Great "ar-tickle", Eric! I like your writing style, too! A few comments...

    Done that. Had a surplus HV xfmr (a few hundred VA) that pegged my VTVM, drew LOTS of primary current and made a nasssty buzzing sound. Needed low V at high A for the Handbook "An RF-proof 30-Amp Supply". I hombrewed the PCBA so I decided to rewind the xfmr. I had nothing to lose and everything to gain! After unwinding a few miles of hair-thin secondary wire, I found the other end had arced thru the bobbin to the core. A few layers of tissue paper + High Voltage Glyptal, and the bobbin was repaired. I found several feet of 8ga wire at the local motor rewinding shoppe. They thought I was nuts for trying to rewind my xfmr. Well, I was. But, my transformer worked just fine... the PS poops-out (drops out of regulation) at just over 25A. Bottom line: it ain't tough if you do some reading first.

    Also known as a "Chicken Stick". I've also heard it called a "Jesus Stick". I'm not sure if that's because it prevents the Boatanchorologist from meeting JC prematurely, or if it's what you exclaim when you discharge a very healthy capacitor!

    Hmm... I've never suffered any long-term ill e-f-f-f-f-f-ects. ;)

    vy 73,
    Bryan WA7PRC
     
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  9. WB1EAD

    WB1EAD Ham Member QRZ Page

    EXCELLENT!..EXCELLENT!

    Congrats to Eric and all!..all this makes excellent resource for diving into the world of "boatanchors"..decent honest hints/kinks are given here..these postings should be a "must" for anyone about to get going on that SX101/NC183 or even an S-120..only thing I can add is do ur best to find that rare ol'time "tech" in ur neighborhood..the guy who used to service mom and dads TV back when "tubes" were king..this person can be ur mentor/teacher or the one who CAN fix ur tube type "boatanchor" and bring it back to life if need be..nope tube technology ain't taught no more and basic troubleshooting is a thing of the past..so if ya do come across someone like that..it's about the same as coming across an SX88 at a rumage sale for $5....if that fails you've got urself some fine ol' "buzzards" here who'll do the best they can to answer ur queries..... 73 de DAVE
     
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  10. K8ERV

    K8ERV Ham Member QRZ Page

    I think you mean "dry" electros. Preceeded by wet ones, which were much more fun when overloaded.

    TOM K8ERV Montrose Colo
     
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