Radio Habana Cuba: Dxers Unlimited midweek edition for May 30, 2000
By Arnie Coro, radio amateur CO2KK
Hi amigos worldwide !!! Welcome to the mid week edition of Dxers Unlimited, your favorite listener oriented radio hobby show with both beginners and experts always in mind. I am Arnie Coro, radio amateur CO2KK your friend here in Havana, and here is the menu for today: another geomagnetic disturbance in progress, and this one apparently escaped scientists' forecasts... YES, we have yet to learn a lot about our nearest star, and how it interacts with planet Earth.
Item two: the very popular "you have questions and Arnie answers" section of Dxers Unlimited will deal today with a request by a loyal listener regarding his Blaupunkt vacuum tube receiver, a radio he describes as his beloved Blaupunkt. If you happen to own and operate vintage vacuum tube receivers, then stay tuned and tape this show, or take notes, as I will provide Jim in New Jersey with information on how to deal with his radio's breakdown...
Item three: VHF-UHF contest coming up, and here in Cuba a national FM VHF contest will take place, too; this is going to happen during the second weekend of June, when the probability of sporadic E propagation is expected to be at its peak.
Item four: More than seven hundred persons are expected to attend the upcoming Cuban National Amateur Radio Convention, which will take place at two central Cuba tourist resorts, Playa Ganuza and Playa El Salto. The main topic of the convention is going to be the technical side of amateur radio, and three prizes will be awarded to the three best presentations... ALL this, and maybe a bit more, right here on this RHC frequency you are now tuned to... Stay with me here, I'll be back after a brief musical interval...
You are listening to Dxers Unlimited, coming to you from Radio Havana Cuba's shortwave transmitters. Our INTERNET e-mail address is inforhc@ip.etecsa.cu again inforhc@ip.etecsa.cu, and VIA AIR MAIL you can get in touch by sending your signal reports, comments about the show and radio hobby-related questions to Arnie Coro, Radio Havana Cuba, Havana Cuba.
Latest solar-terrestrial data show both the K and A indexes moving up, A index passed the 20 mark Monday, and the K index at the time I was writing the script for this show was 3. So, be on the lookout for abnormal propagation conditions that might bring in some rare DX stations to your receivers.
Item two: Jim from New Jersey wrote me a long e-mail message, explaining how his vintage Blaupunkt receiver, a Verona US version type 2608, AM-SW-FM vacuum tube model had failed due to a burned out power transformer. Amigo Jim, you have to be really extra careful because the burned out transformer may be not a failure of the transformer itself, but some other vital component shorting to ground, and if the radio did not have the appropiate fuse installed, then the transformer would had gone up in smoke... So, let's do an analysis of how to repair the receiver you describe as "my beloved Blaupunkt."
First of all, you must be absolutely sure that the diode rectifier module type B250-C75 is replaced either with a new one, or with a set of properly wired silicon diode rectifiers. To the best of my recollection, the B250-C75 rectifier module is an ancient component, assembled from four selenium rectifiers. There is one easy, but not too comfortable way of learning if any or all of those selenium rectifiers in the module are no longer useable: Just hold the rectifier module close to your nose, and smell the part. If you detect an odour somewhat similar to rotten eggs, then you can be sure the selenium rectifiers are no good. Traces of selenhydric acid are the cause of the rotten smell around damaged selenium rectifiers. Now, here is Arnie Coro's advice: replace the rectifier module with set of silicon high peak reverse voltage avalanche diodes, which can be wired on to a small circuit board cut to exactly the same size of the B250-C75 selenium rectifier module. Now, phase two: Once you have the correct receiver schematic diagram, it is a very good idea to check all the electrolytic capacitors in the power supply. The ones on your receiver are no less than 40 years old, and now that you are doing a major overhaul, this is a very good thing to do: Make a list of all the electrolytics, both high and low voltage, and replace them with new ones -- but before installing the new ones, you should cycle them trough a very important reforming process that I will describe in my direct e-mail answer to you. Last but not least, be sure to check the radio's current demand using an outboard power supply.
Once you are sure that the radio is not drawing excessive current from the B PLUS supply, then you can proceed to install the new power transformer... AND, do not forget to place a fuse of the appropiate current rating in series with the transformer's primary. Let me tell you that to those excellent vintage receivers I like to add an extra B PLUS line fuse, which will pop if any of the receiver's components placed across the high voltage line happens to fail. It is a lot easier to replace a fuse, and a shorted bypass capacitor, than to have to replace a power transformer. OK amigo Jim, I think you now have a very clear picture of how to proceed with your collector's receiver. Again, do not install the replacement power transformer until you are absolutely sure that the radio's current drain is within specifications. AND, as always, if you are in doubt, just e-mail me and I'll be more than happy to help you and all Dxers Unlimited's listeners with that wonderful aspect of the radio hobby, restoration of vintage sets!!!
In a few days time the VHF-UHF bands will see a lot of activity. As usual during the second weekend of June, radio amateurs try to work as many VHF-UHF stations as possible. Here in Cuba a national VHF contest mobilizes the nation's enthusiastic FM 2 meter band operators. By scheduling the Cuban FM 2 meter contest during the same weekend, there is always the chance that a nice sporadic E or a tropo duct opening will allow participants in the contest to add many new grid squares and call areas to their logs. Be on the lookout for the Cuban FM 2 meter band operators which will concentrate in the segment between 145.5 and 145.8 megaHertz. Many of the Cuban operators will be using high gain vertically polarized antennas with which they have already achieved excellent DX results during past contests. So if you plan to operate during the upcoming June VHF contest, do listen to the segment between 145.5 to 145.9 megaHertz for cuban FM simplex stations that will be participating in the both the cuban national and the international contests at the same time.
Another news item from the growing Cuban amateur radio community: The National Amateur Radio Convention is to take place this coming weekend, and according to my sources, more than 700 participants will attend this gathering which has as its main topic the technical aspects of amateur radio. Three prizes will be awarded to what a jury of distinguished radio amateurs will consider the three most important contributions to the technical development of the hobby. Listening to the 40 meter amateur band this past weekend, I learned about several QRP or low power transceivers designed and built by Cuban radio enthusiasts that will be shown and operated both at Playa Ganuza and Playa El Salto. Several 2 meter band low-cost antennas will also be submitted to the jury, and I expect that the members of the jury will have a really hard time awarding those three valuable prizes. The Cuban Federation of Amateur Radio Operators is sponsoring this National Convention, at which a flea market, parts and components exchanges and technical forums will also take place.
And now amigos, as always at the end of the show, here is Arnie Coro's exclusive and not copyrighted HF plus 6 meters propagation update and forecast... Solar activity is moving down, but we may soon see some kind of a surprise upswing in activity ahead of schedule for this solar rotation. Scientists continue to monitor the sun with their newly discovered solar surface waves detection procedure, which is obviously providing a lot of information that was previously not available. Solar flux should theoretically bottom to around 130 units at the end of this rotation, but be on the alert, as I am keeping an eye on two new active regions that may change the picture quite radically at any time now. Best Dxing conditions continue to occur after your local sunset, with the 20, 17 and some days the 15 meter band open deep into your local nightime hours. For shortwave listeners, this means that those bedside radios should be tuned to both the 16 and 19 meter bands for possible DX, away from their usual tuning spots on the 6 to 12 megaHertz segment of the HF spectrum. For TV DXERS and FM band DXERS we are now right into the Sporadic E skip season upswing, so keep those TV sets tuned to the lowest local empty channel in order to detect early signs of sporadic E skip. Finally, don't forget to send me your nice sporadic E DX loggings to inforhc@ip.etecsa.cu, together with your comments about this show, and if you have any radio hobby related questions, here we are at your service to answer them. Air MAIL to Arnie Coro , Radio Havana Cuba, Havana Cuba, see you at the upcoming weekend edition of this show, next Saturday and Sunday UTC days.
Arnie Coro CO2KK
Havana, Cuba
May 30, 2000Postal address:
Arnie Coro, "Dxers Unlimited"
Radio Havana Cuba
PO Box 6240, Havana, CUBA 10600
phone: 53-7-814243
phone res: 53-7-301794
To Arnie Coro's Dxers Unlimited
Back to NY Transfer's RHC main page