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#1
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I am not sure if the capacitance of the power diodes would be too high. This
could cause poor isolation, but if you reverse bias the unused filter diodes, they might work. Pete wrote in message oups.com... Thanks for the info and advice Pete. I recently saw a comment that standard 1N4002 type (60 Hz) diodes are actually good replacements for the PIN diodes on the front-end band pass switching networks. Have you heard of this? Frank Pete KE9OA wrote: Hi Frank, That is a nice receiver, and the mods that you have done seem to cover everything. The only thing that I can recommend....if this receiver uses diodes to switch the input bandpass filters, I would replace them with 1N5767 PIN diodes. Bias them at around 60mA. I think that you can run up to around 90mA, but that might be pushing them. Philips also has some suitable PIN diodes, but you want to make sure that you have a long enough minority carrier lifetime. Congratulations on the new receiver! I haven't picked up anything new for awhile, except that NRD-91. Pete wrote in message oups.com... Hi Pete; I just recently acquired an essentially mint Icom R70 off of Ebay. It has the 500 kHz CW narrow filter included and came with the manual and original box. After using this radio for a couple of weeks I'm very impressed short of the weird ergonomics and the end of band tuning anomalies. The sensitivity and selectivity are superb and the BP shift and IF notch are among the best I've used. The audio is a bit on the shallow side but I replaced a few of the electrolytic coupling caps with film caps and the difference was very noticeable. I also removed the LW/MW input attenuator and disabled the input rf amp defeat for MW/LW. It can now be switched on and off from the front panel switch. What is your experience with this radio and are there any other improvement modifications that you know of? Comments on this receiver from others are welcome. Frank K3YAZ Tucson |
#2
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"Pete KE9OA" ) writes:
I am not sure if the capacitance of the power diodes would be too high. This could cause poor isolation, but if you reverse bias the unused filter diodes, they might work. Pete I seem to recall reading that some of the 1N400X series have a structure like PIN diodes, I think some of the higher voltage ones. This has been stated in various places, though I have no idea about whether it's a valid solution for this specific receiver. Michael wrote in message oups.com... Thanks for the info and advice Pete. I recently saw a comment that standard 1N4002 type (60 Hz) diodes are actually good replacements for the PIN diodes on the front-end band pass switching networks. Have you heard of this? Frank Pete KE9OA wrote: Hi Frank, That is a nice receiver, and the mods that you have done seem to cover everything. The only thing that I can recommend....if this receiver uses diodes to switch the input bandpass filters, I would replace them with 1N5767 PIN diodes. Bias them at around 60mA. I think that you can run up to around 90mA, but that might be pushing them. Philips also has some suitable PIN diodes, but you want to make sure that you have a long enough minority carrier lifetime. Congratulations on the new receiver! I haven't picked up anything new for awhile, except that NRD-91. Pete wrote in message oups.com... Hi Pete; I just recently acquired an essentially mint Icom R70 off of Ebay. It has the 500 kHz CW narrow filter included and came with the manual and original box. After using this radio for a couple of weeks I'm very impressed short of the weird ergonomics and the end of band tuning anomalies. The sensitivity and selectivity are superb and the BP shift and IF notch are among the best I've used. The audio is a bit on the shallow side but I replaced a few of the electrolytic coupling caps with film caps and the difference was very noticeable. I also removed the LW/MW input attenuator and disabled the input rf amp defeat for MW/LW. It can now be switched on and off from the front panel switch. What is your experience with this radio and are there any other improvement modifications that you know of? Comments on this receiver from others are welcome. Frank K3YAZ Tucson |
#3
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Now that I think of it Michael is correct. It was the 1N4007, the 1 kV
version of this slow diode that was recommended. It would tend to have lower junction capacitance because of the wider depletion region due to the heavier doping for the high voltage standoff. Once the diode is biased on dc wise, the forward drop is not significant because it doesn't "switch" with the signal current. I think the trend to Schottky diodes was because of the lower intrinsic capacitance. Frank Michael Black wrote: "Pete KE9OA" ) writes: I am not sure if the capacitance of the power diodes would be too high. This could cause poor isolation, but if you reverse bias the unused filter diodes, they might work. Pete I seem to recall reading that some of the 1N400X series have a structure like PIN diodes, I think some of the higher voltage ones. This has been stated in various places, though I have no idea about whether it's a valid solution for this specific receiver. Michael wrote in message oups.com... Thanks for the info and advice Pete. I recently saw a comment that standard 1N4002 type (60 Hz) diodes are actually good replacements for the PIN diodes on the front-end band pass switching networks. Have you heard of this? Frank Pete KE9OA wrote: Hi Frank, That is a nice receiver, and the mods that you have done seem to cover everything. The only thing that I can recommend....if this receiver uses diodes to switch the input bandpass filters, I would replace them with 1N5767 PIN diodes. Bias them at around 60mA. I think that you can run up to around 90mA, but that might be pushing them. Philips also has some suitable PIN diodes, but you want to make sure that you have a long enough minority carrier lifetime. Congratulations on the new receiver! I haven't picked up anything new for awhile, except that NRD-91. Pete wrote in message oups.com... Hi Pete; I just recently acquired an essentially mint Icom R70 off of Ebay. It has the 500 kHz CW narrow filter included and came with the manual and original box. After using this radio for a couple of weeks I'm very impressed short of the weird ergonomics and the end of band tuning anomalies. The sensitivity and selectivity are superb and the BP shift and IF notch are among the best I've used. The audio is a bit on the shallow side but I replaced a few of the electrolytic coupling caps with film caps and the difference was very noticeable. I also removed the LW/MW input attenuator and disabled the input rf amp defeat for MW/LW. It can now be switched on and off from the front panel switch. What is your experience with this radio and are there any other improvement modifications that you know of? Comments on this receiver from others are welcome. Frank K3YAZ Tucson |
#4
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#6
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#7
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Oftentimes, it is the type of ferrite material used in the mixer baluns.
Also, it could be that low Q caps are being used in the lower bands. I have both an NRD-515 and an NRD-91. Both of these receivers exhibit rolloff below 700kHz. These comparisions are made, using a Drake R7, Palstar R30, Yaesu FRG-100, Icom R-75, Lowe HF150, HF-225, and HF-250. I did repair a Kenwood R-2000 a few years ago, and wondered if it had some sort of attenuation below 1.5MHz. I noticed this same characteristic with a Kenwood R-5000 and an AOR-3030. Pete wrote in message ps.com... wrote: There's no question that the 1N400X series is a poor switching diode when it comes to speed and reverse recovery characteristics, however, for switching in and out bandpass filters I think the reverse bias junction capacitance is the major issue to prevent unwanted signal coupling. I would definitely look for true PIN diodes if I were upgrading the filter switching diodes rather than use 1N4007s. It's just interesting that there have been articles on the fact that they appear to work reasonably well in some cases. I know the Kenwood R-2000 I had used the equivalent of 1N914s for these diodes in the front end and they were horrible with all kinds of cross talk from stronger, out of band signals. Frank --------------- The R2000 uses BA282 band filter switch diodes. The RX Unit (X55-1340-00) in the R2000 sevice manual gives the part number, which I just verified by looking at the stock diodes that I saved when I upgraded both of my R2000s. See http://www.vishay.com/diodes/list/product-85526/ For the 6MHz and 9MHz bands, good HP PINs give a slight but noticable improvement. I expected a big improvement in the below 500KHz range but found nothing that I could hear. I still lurk and will make the odd post when I have something usefull to add. All prior Email accounts are abandoned and dead. Terry |
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