Radio Habana Cuba: Dxers Unlimited weekend edition for June 17, 2000
By Arnie Coro, radio amateur CO2KK
Hi amigos! This is the weekend edition of your favorite radio hobby show on short-wave. I am Arnie Coro, radio amateur CO2KK, your host here in Havana, and it's my pleasure to share with you about a quarter of an hour of all radio hobby related information. Join me and have fun!!!
Item one: Excellent propagation conditions are prevailing now on the 21 megaHertz or 15 meter band during your local evening hours... Yes, hard to believe that 15 meters will be open at 9 o'clock in the evening and even later, but that's what's happening, so here is Arnie's advice, monitor 15 meters starting right at your local sunset, and keep your radio on until you go to bed. Some examples of what I have worked here from Havana Friday evening local time, or Saturday UTC day, later in today's Dxers Unlimited.
Item two: Older amateur transceivers and receivers which are all solid state are a lot more difficult to repair than vacuum tube equipment, and sometimes they can be found at hamfests and fleamarkets at very low prices, precisely because they are non operational... Their value as a source of electronic components is usually very limited, but stay tuned, and I'll tell you about some success stories repairing solid state radios built during the nineteen eighties and early nineties and which failed. I'll be back in a few seconds with more radio hobby related information coming to you via Radio Havana Cuba short wave transmitters.
You are listening to the weekend edition of Dxers Unlimited, and here is item three: Scientists are now talking about a new kind of vacuum tube that requires no heater, in other words, a cold cathode device, which may bring back electronics into a second vacuum tube era... According to recent publications, the ultra miniature vacuum tubes could replace solid state devices in many critical applications. But, this is not around the corner and will probably take a few years to mature, so in the meantime, if you do want to play with vacuum tube circuits, there is no choice but to use whatever devices are available. Something that really amazes me is the lifetime of properly built vacuum tubes. A Dxers' Unlimited listener recently wrote telling me about his regenerative receiver, a replica of a 1920's set, in which he was using tubes that were actually built in the late nineteen twenties, and which proved to be in perfect operating conditions, despite the fact that more than 70 years have elapsed since their date of manufacture which, by the way, was clearly marked in the original tube packing cartons. Building replicas of those sets is a lot of fun, and let me tell you that one learns a lot about radio receivers that show unbelievable performance, when you learn how to use the controls. These are hands-on radios, they do need you to play with the controls in order to optimize reception, but again, it is absolutely amazing how sensitive and how selective they can be. I built a universal vacuum tube audio amplifier for those experiments, using 1950's technology, and now all I need to do when testing yet another regenerative vacuum tube receiver configuration is just build the RF amplifier and regenerative detector stages, using the already-built 12AX7 - 6AQ5 audio amplifier, which provides enough audio to fill the room, and has a rather low noise level and little distortion due to the proper use of negative feedback. The audio amplifier and the power supply for the vacuum tube receiver experiments are all housed in a chassis, with power plugs and terminal strips from where to get the filament and plate and screen voltages to the experimental circuits. It took two weekends to build in my spare time, but it was well worth the effort.
YES, AMIGOS, vacuum tube regenerative receivers are fascinating to say the least, and you can use a crystal controlled converter connected in such a way as to produce a super-heterodyne receiver that uses a regenerative detector, a combination that provides fantastic performance! Go ahead and search your nearest library for radio books of yesteryear, and soon you may find yourself playing around with some of those really fascinating circuits with which our ancestors enjoyed their hobby!!!
This is Radio Havana Cuba, the name of ths show is Dxers Unlimited, and yes amigos, we do QSL 100 percent here. Send your QSL requests with a signal report and comments about the show directly to me: arnie@radiohc.org, or via AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba and we will be QSLing back to you as soon as possible.
Now back to item one; remember, at the beginning of the show, when I mentioned that 15 meters was now open during the local evening hours to nice DX locations? Here are the examples: in less than an hour, operating CO2KK with 50 watts SSB single side band voice, my 40 and 15 meter wire beam brought DX from southern Chile, Kuwait, Oman, Israel, Germany and Poland...with like-local signals in some cases. The station from Oman was booming in here, and Ed 4Z4UR near Tel Aviv was pinning my S meter to the very end of the scale. As old-timers in the hobby like to say, when propagation conditions are good, low power and a wet string for an antenna will let you work the world!!!
Now back to item two: From time to time, I receive an e-mail from one of Dxers Unlimited's listeners asking for advice... the question is usually related to a piece of used equipment that may be available at very low price. The rig is usually described as one of the 1980's or early 1990's transceivers. It may be an HF radio, or an FM 2 meter or 70 centimeter set... Then, in some cases they tell me that the radio's display is blank, showing nothing. "Arnie, do you think that this transceiver may be recovered??" Now, that is a really tough question. In some cases, someone with the circuit diagrams, technical information manual and a lot of know-how can bring back to life one of those dead transceivers... and in other cases, fault-finding and repairs are extremely difficult, and sometime almost impossible. But don't be discouraged; you could be lucky and get yourself a nice rig at a rock-bottom price! There a few useful tips when dealing with "dead" solid state transceivers. Just two days ago, I brought back to life a nice two meter FM set, a 25 watt Kenwood, just by disconnecting very carefully all the connectors between the different boards, spraying them with contact cleaner, and re-connecting them back. This must be done very slowly, and you should by all means avoid breaking wires that go to the connectors. Obviously, this almost-20-year-old radio was a victim of poor contacts at the connectors, and that was it -- but let me warn you that not every "dead" solid state transceiver or receiver is so easy to repair.
And now that I mentioned the Kenwood rig, let me tell you that many of them built during those years act intermittently or fail completely due to some problems with plated-through holes that the Kenwood factory had for a long time. With a lot, and I mean it-- a lot-- of patience, someone with good eyesight may put wires on each plated-through hole, and in many cases the radio will come back to full operating condition and will never again fail due to poor contacts in the plated-through holes.
So, maybe you can find yourself a TS140, a TS430 or perhaps a TS440, or a 2 meter TR7800, which is non-operational, proceed to check all the board-to-board connectors, and if that does not work, then proceed to very slowly and patiently solder wires through every plated-through hole in the printed circuits. And, as I said, maybe that will be all you will have to do, although in some other cases other problems may be present too, like fried output transistors, a quite common defect. So, good luck with any attempts to revive one of those solid state receivers or transceivers, built during the nineteen eighties and early nineties!!!
And now amigos, as always at the end of the show, here is Arnie Coro's HF plus 6 meters propagation update and forecast: Solar flux reached the maximum for this solar rotation this week, and from now on, unless a new or more than one new active regions appear, solar activity will be moving down. We may expect yet another geomagnetic disturbance by late Sunday or as late as mid-Monday UTC, due to a coronal mass ejection stream of particles that is presently travelling towards the Earth's magnetosphere. Expect excellent propagation during your local nighttime hours, with the MUF -- or maximum useable frequency -- going as high as 22 megaHertz on some East-West path, something that is really remarkable, and I will explain why it happens during our next Dxers Unlimited's mid-week edition, next Tuesday and Wednesday UTC days. Six meter operators, and TV and FM band Dxers, should constantly monitor the bands for rising MUF due to sporadic E events that may occur even late in the evening.
Enjoy radio, amigos, and if you have any comments about the show, what you like about it and what you don't, please send it to arnie@radiohc.org with a signal report and any questions you may have about the hobby, too. See you on the amateur bands; it is always a great pleasure to have a nice QSO with Dxers Unlimited listeners!!!
Arnie Coro CO2KK
Havana, Cuba
17 June, 2000Postal address:
Arnie Coro, "Dxers Unlimited"
Radio Havana Cuba
PO Box 6240, Havana, CUBA 10600
phone: 53-7-814243
phone res: 53-7-301794
e-mail: arnie@radiohc.org
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