50MHz Modification Pages ------------------------------------------------------------------------ Any additions/Mods? then please Email us at: equinox@itl.net Look at the Back Issues of Internet Six News. 50MHz CD Rom Update Here Try the: 50MHz Dx Cluster: Check out the World 50MHz QSL Listings. and the New Beacon List. ------------------------------------------------------------------------ SB220 50MHz Modifications 1) Move the 10-meter tap on the plate coil (L6) to a point 1-2/3 turns from the plate-tune capacitor. A grid-dip oscillator can be used to check resonance at 50 MHz. 2) Unwind the 10-meter input coil (L1), leaving 2-3/4 turns. 3) Replace C33 and C34 by a single 10 pF mica capacitor. 4) Change C35 (115 pF) to a 33-pF mica capacitor. This change to my SB-220 has proved to be an excellent addition to the 6-meter setup. - John Roth, WA2TSJ ------------------------------------------------------------------------ Azden PCS-7500H Mods The BEEP mod is very simple. The Azden has a loud beep every time you push ANY of the buttons on it. After a while, you get tired of it. Not only is it loud, but it's long (1/2 second). The BEEP mod consists of clipping one wire from CN6 (connector 6) and insulating it. It injected the beep tone into the AF portion of the radio, so by removing the input, you get no beep. The OBTX mod is the out of band transmit mod. The OBTX is very simple. Just remove one leg of diode D-127. ....... Darryl Linkow KE6IHA ------------------------------------------------------------------------ TS690 Mods. Mods for your Kenwood TS690 - by Tuomo OH1LEU Six News.......... In issue 36 of Six News there was an article concerning the Kenwood TS690. A few questions were asked. I hope the following information will answer a few questions, including the 30 - 50MHz coverage. I have a 690 bought direct from the States and my friend Kari OH1MLD has one bought from Finland. We have been comparing the differences between models! All band assignments are controlled by diodes in the digital unit, which is located behind the front panel. There are several (probably) yellow 4148 look-a-like diodes in a row, marked D20-D23. D23 affects the rx range. Removing it opens the receiver from 30KHz (yes!) to 60MHz continuously. Also any frequency change can now be controlled directly from the keyboard. D20 may have something to do with the WARC bands, at least in the US model there is only one diode D21, so you might like to try taking others away. Also the logic changes when entering a new frequency because of the "new bands", so be careful when you decide to operate! If you want to make these mods, take both covers off, note the extra filters, which are now the highest parts of the rig and note also that those little flat cables coming from the digital unit can very easily break. After that, loosen two lower screws (on both sides) that are securing the front panel and take away the two upper screws. Now the front part can be twisted downwards. Diode D23 can be removed easily from the digital unit PCB, located at the right hand side. You may also like to make some changes to the mic gain scaling. It is very easy to overdrive the PA. Between the mic gain pot and the centre tap is a 10k resistor, which causes the mic gain to be somewhat non-linear. Changing this resistor between centre tap and ground, still results in a non-linear pot, but, if for example I had the mic gain at 9 o'clock now I can turn it to nearly 12 or even more. This is very handy when using the processor, the ALC setting is now not as critical. The maximum gain remains the same. You may have noted that the AM band has poor sensitivity. You may change the coupling in the RF-unit on that particular band 500KHz - 1.6MHz. The coupling has two 39 ohm resistors (R6,R7) in series, controlled through a 10 ohm resistor (R8) between them. Changing the 10 ohms to a miniature coil 1uH and those 39 ohms to 0 ohms makes AM sensitivity much better. If you live near a AM station forget this mod! The SMD components are located in the RF-unit, from the CN4 connector and IC2 towards the centre of the PCB, at the opposite end to the filters. I would recommend the purchase of a service manual before undertaking these mods. I also can not be held responsible for any damage Hi! 73 de Tuomo OH1LEU. **Note** Cutting D23 reverts the 690 back to Japanese spec i.e. full Rx coverage up to 60MHz but only 50w o/p on 10m due to their regulations. (Thanks G0HVQ) ------------------------------------------------------------------------ SB-200 "Conversion" I have received several queries on conversion of the SB-200 for operation on 6 meters and thought I'd summarize what I've found. I know of three published conversion articles. Listed below is a summary each. "Using The Heath SB-200 Linear On Six Meters" by Henry Blodgett, W2UTH/W2FRL in January 1969 QST. Operation on HF is maintained - 40 meters is eliminated and the taps are moved up on the band switch so that a spot for 6 meters is available. A tap is added to the 10-15 meter coil for 6 meter operation. Plates are removed from the existing tuning cap to allow coverage of 6 meters. The 40 meter input coil is re-wound and the associated capacitor is changed. With 900 watts of input power (Driven by a Heath SB-110) 450 watts output is obtained. "Improvements to Using the Heath SB-200 Linear on Six Meters", by Ron Klimas, WZ1V, published in the 1995 Eastern VHF/UHF Conference Proceedings This article provides Ron's experience with the QST conversion. Ron states that he has been using the converted SB-200 on 6 & 75 meters since 1982. Ron recommends removal of the SWR/Relative Power monitoring circuitry, the usage of coaxial SPDT relays to replace the original open frame type relays and the usage of good quality coax in the RF output circuit. With these changes a major improvement in RF efficiency is obtained: 600 watts out instead of 400, He also recommends new plate parasitic suppressors, beefing up the cooling and replacing the HV rectifier stack. I believe both of these articles are available from the ARRL for a nominal charge. "Six-Meter Conversion of the Heathkit SB200 Linear Amplifier" by Louis Savioe, K1RAK in November 1971 Ham Radio magazine. This conversion is more extensive. It replaces the existing output PI network with new capacitors and coil and HF operation is no longer possible. The plate parasitic suppressors are modified. The 10 meter input coil is modified and the associated capacitor is changed. A RG-8/U coax run and a Z-50 RF choke are added. 600 watts out for an SB-110 drive power of 60 watts is obtained. Since HR was bought by CQ you might be able to get a reprint/copy of the article from them - I haven't checked this out. Conversion Success/Problems I have yet to hear from anyone who has had extensive problems with the QST article conversion. I have heard from several who have instability problems with the HR article conversion - including me. My next step is to incorporate several of WZ1V's recommendations into the HR conversion to see if that improves stability! 73 & Good Luck! Bob..... W3RW ------------------------------------------------------------------------ Pass Band Tuning for the ICOM IC-575 By Adam Maurer, VK3ALM/VK3YWV ************** Six News Issue 40 ************** Icom's IC-575 6/10 metre transceiver like its other brothers in the x75 family is a fine transceiver, as many owners will attest to. The early versions of the x75 rigs had Pass Band Tuning (PBT), a feature left off later models due to a dispute that erupted between companies. With minimal effort this feature can be re-instated. Additionally, an improvement in 2nd I.F. selectivity also results. The PBTless models have instead a "Data Level" control which adjusts the level of the external audio input from the accessory socket on the back of the rig. The most obvious use for this is for a RTTY/packet modem. As far as I am concerned this "Data Level" control is of dubious value, as the audio level can easily be adjusted outside of the radio, and it would rarely need to be adjusted once it has been set correctly for the particular device feeding the transceiver. Interestingly the "Data Level" pot is still a centre-detent type like the original PBT control. Examination of the schematic reveals that it is the same value, 10K, as the original. Furthermore, the PBT line from the D.A.S unit is now connected to a fixed-value resistive divider, made up of two 4K7 resistors. Hmm! A comparison between the "old" schematic and the "new" schematic also shows that a ceramic filter, FT3, has been deleted from the newer radios, being replaced with a 0.0047uF capacitor. Other than that, everything else is still there. When you think about it, it is the obvious and cheap way out for Icom to remove this feature by making minimal changes to the design and to "hard-wire" the PBT to the centre position, rather than making major changes to its production run. The "missing filter" Before you start to pull the radio apart, you will need to purchase a Murata CFJ455K5 filter. The specifications of this filter are; Centre frequency: 455KHz, Bandwidth: 2.4KHz @ -6dB, Passband Ripple: 2dB, Input Impedance: 2K ohm, Output Impedance: 2K ohm. Modification procedure: 1: Remove all connections to the set, eg; power, antenna, mic, accessory leads etc. 2: Remove the 9 screws holding the bottom cover. Position the radio so the front of it is towards you. All the mods are done to the main unit PCB (the largest PCB). 3: Remove the six screws holding down the main unit PCB. (or is that seven??? I have a habit of losing the damn things!) 4: Disconnect the coaxial lead plugged into J2 on the right hand side of the main unit PCB. 5: Disconnect the internal speaker feed to J17, located at the rear right hand side of the PCB, next to the external speaker jack. Disconnecting these two feeds will make is easier to turn the PCB over to gain access to the solder side. 6: Carefully pry the PCB loose. The "Ext Sp" and "Key" jacks on the back of the PCB make this quite awkward. The PCB will need to move towards the front of the radio in order to clear the rear panel. 7: When it is in the clear, the rear side of the PCB can now be flipped over. 8: Remove C279 (0.0047uF). This is located front left. 9: Remove the link near C279 designated as W159. 10: Desolder the other nearby holes associated with the filter. (These holes will be immediately obvious if you have a look at the pin-out of the filter). 11: Solder the CFJ455K5 filter in position. 12: Re-orientate the PCB back to its normal position. 13: The blue wire going to the PCB just near J10 needs to be cut, preferably as close to the pin as possible. J10 is located front left of the PCB, near where the filter was just installed. You will find this much easier to do if you temporarily remove the connector plugged into J10. This blue wire is the "PBTV" line, the Pass Band Tuning Volts line, and was fixed to +4 volts, ie; set for the centre of the "normal" passband. Now there are a number of ways of providing this line with the adjustable 0 - 8 volts that is required. I shall now describe the method I used - using the (waste of space) "Data Level" control. 14: Disconnect the connector that goes to J20. This is the feed that goes off to the "Data Level" pot. Put this aside for now. 15: Desolder and remove J20 from the PCB. 16: In J20s place I mounted a vertical 10K trimpot - see diagram. The trimpot leads will need to be bent in order to fneed to be bent in order to fit, and the wiper will need a small length of wire added to it so that it makes the distance to the hole in the PCB. This allows you to retain the "Data Level" control, albei 17: The main unit PCB can now be re-fitted and screwed back down. Do not forget to re-connect the coaxial lead to J2 and the internal speaker fed to J17. This male connector is now used for connecting +8 volts, ground, and the PBTV line to the pot. 18: So, on the "old J20" male connectors we now need, matching the leads from the pot on the female connector: Red (wiper) connects to the blue wire (PBTV line) Braid (CW end) connects to Ground White (CCW end) connects to +8 volts There are many spots around the PCB to obtain +8 volts and ground from, but the easiest spot to access is IC15, a 4066. This is located just to the rear of the (big) 9.0105MHz crystal. Connect to pin 14 for +8 volts and pin 7 for ground. 19: To prevent shorts, tape over where you have soldered the wires to the (J20) connector. Making use of these connectors, rather than cutting them off and soldering the wires directly to each other, improves access and serviceability to the main unit PCB, should that be required at a later date. 20: Alignment: As it stands, it is not absolutely necessary to tweak anything but if you are fastidious about alignment and have an accurate digital frequency meter, hook it up to the "test point" at R209, a 100 ohm resistor. Those of you with an IC575 service manual can refer to page 2-4 for PBT alignment. For those without here is the procedure anyway: 20-1: With the radio receiving on the AM mode and PBT set to full CWW, adjust L17 for a frequency of 9.46830MHz. 20-2: Centre the PBT control. Adjust R90 for 9.46500 MHz. 20-3: With the PBT still centred, change to USB mode and adjust R93 for 9.46650MHz. 20-4: Change to FM mode. Adjust R95 for 9.46650MHz. (Adjusting the PBT whilst in FM mode should make no difference to this). 21: Before you screw the bottom cover of the radio back on you had better adjust the "Data Level" trimpot to suit your requirements. Make sure you have reconnected the internal speaker feed to J17, the coaxial lead to J2, and the connector to J10. 22: Refit the bottom cover and screw in the nine screws. 23: Reconnect power and antenna feeds and confirm normal operation. Checkout: Place the "new radio" into USB mode and note the enhancement of the highs at the CW end of the "Data Level" control, err make that the PBT control, and the enhancement of the lows at the CCW end of the control. Now place the radio in the LSB mode and note the complementary effect. Needless to say, any modifications done outside of an Icom service centre will no doubt void any warranties on the radio. Having the PBT features has been handy when trying to zero-beat TV carries, although the bass response of the pathetically small internal speakers is not particually good. A larger external speaker or headphones here will help. The poor bass response could be improved by increasing the value of C192, a 0.1uF capacitor in the audio line, although I never bothered. I get the impression that the PBT feature would be more useful in Europe than it has proved to be over here in VK, for the simple reason; there are not as many 6m ops over here - even with Es - so QRM from another nearby station is rare. Happy "PBTing" and good DX! 73 Adam VK3ALM/VK3YWV. ------------------------------------------------------------------------ IC706 MODS de VK3ALM Several IC-706 (MK1's) here in Melbourne have exhibited faults whilst transmitting in the FM mode only, the symptoms being; 1) Low O/P power (generally squillywatts, enough to be heard on a nearby receiver on the shack bench but that's it). 2) Carrier frequency is NOT what is indicated on the dial. Typically 5 - 30kHz low. 3) Carrier tends to wander and sounds spurious. Having taken mine back to Icom twice already for the same fault, I was not prepared to be inconvenienced a third time. Upon checking the Faults Reports I noticed that the "FM VCO" had been tweaked. There is a 9Mhz VCO operated during FM mode only which is modulated from the mic amp. To cut a long story short, C267 was not re-flowed to the PCB to a satisfactory standard. (Shouldn't this product meet IPC Class 2 ?) There was insufficient solder paste applied during the printing process and the end result being an intermittent solder joint. I re-touched both pins of C267 with a fresh solder using a good ol Weller with PTA-7 tip, and it's performed faultlessly since. Potentially this transceiver could have gone back to Icom until the cows came home! (Until they realised it was a crook solder joint and not a wandering pot) C267 is a miniature trimmer capacitor located to the right of the 9.0115MHz IF Filter on the Main Unit. Access to the offending area is very easy, and the whole job takes about 10 minutes. Equipment Required: Small Phillips head screwdriver. Frequency Counter. Dummy Load, Power Meter & patch leads. Soldering iron with small tip. Procedure; Turn transceiver off. Disconnect all leads. Using a small Phillips head driver, remove top cover only. With radio upright and front facing towards you (i.e. normal operating position) MAIN unit is the front board. Locate 9.0115MHz IF filter and then locate C267 (identified on silkscreen and is approx 9mm to the right of filter). Carefully re-touch up solder joints to both pins of the cap. Re-connect PWR lead. Connect to Dummy Load via PWR meter. Turn transceiver on. Dial up 29.6 MHz and select FM mode. Check carrier frequency against Frequency Counter. Check PWR O/P is appropriate to PWR setting. If all ok, replace top cover. It is unlikely you will need to tweak C267, as the setting is not that critical, just set it in centre of lock range. Adam Maurer, VK3ALM ------------------------------------------------------------------------ GJ3RAX Additions to above. Symptom - IC-706 Mk 1 would not transmit FM, other modes OK. When transmitting FM, the AF signal is applied to the Voltage Controlled Oscillator Q40. This is phase locked to 9.0115 MHz and is made to deviate about this frequency. If it becomes unlocked and drifts to another frequency, outside the filter bandwidth, the transmit output drops to virtually zero. In order to relock the VCO, the variable capacitor C267 must be adjusted. The DC voltage at test point CP4 needs to be measured with a digital meter as the resistor supplying this point is quite high and would be loaded by a conventional multimeter. The voltage measured should be set to 1.5 Volts. In order to carry out this adjustment it is necessary to remove the top cover of the radio. 5 screws must be removed, 3 on top and one each side. With the front panel facing you the main SSB filter, type FL-30, is seen near the front and behind the LCD display. 5 screws must be removed, 3 on top and one each side. With the front panel facing you the main SSB filter, type FL-30, is seen near the front and behind the LCD display. C267 i These adjustments and locations on my radio conform to the information in the service manual which should be consulted if there is any doubt about this procedure. It is described on page 4-6 of the service manual and the diagram on page 4-7 shows the locations. There could be some differences in later models and I have no experience of the Mk 2 version..........73, Lawrence GJ3RAX. ------------------------------------------------------------------------ Alinco DX70TH Extended Coverage Mods de GJ4ICD The basic radio covers up to 30MHz on RX, but by shorting out a copper plane it can increase the RX to 35MHz. Also the radio can be extended on the 50MHz RX section to 45MHz to 60MHz. Follow the instructions below: Remove the front panel of the radio, remove the 4 screws holding the back on and remove the 2 plugs from the pcb sockets. Remove the back panel, this has to be prised so be careful! lay the unit down on it's face with the optical encoder towards the right. Near the encoder you will see 2 lines of "TRACKS" vertically, short the third pad down on the right-hand set of tracks, this will give you 45 to 60MHz rx. For added rx coverage to 35Mhz short the first pad in the lefthand set (copper coloured and larger than it's lower pads). Do a full reset on the radio after assembly. ------------------------------------------------------------------------ Amp UK PSU Diode mods. Amp UK who produce 50MHz/144MHz amplifiers in the UK use 2 strings of diodes (part of the voltage doubler) in the power supply. It is suggested that these be replaced by 2 high power diodes similar to those used in Microwave Ovens. This is due to mains transients which can and have destroyed just one of the diodes requiring all of the two strings to be replaced, which is good practice. The 2 diodes simply replace each of the 2 strings of 1N4007's and can be obtained from CPC Ltd in the UK or Peter Dahl in the USA. They are HD207 coded, rated at 15kv 1.2 amp and cost about £9 each. The size of these diodes is about 3" long and about 1" square. Microwave Oven service people also keep them. They have fitted inside of them shunt capacitors and transient resistors and are VERY hard to destroy. ------------------------------------------------------------------------