|
TC Dufresne wrote: Hi: I am having a problem with a "Simple Receiver for Beginners". It is from a design that was featured in an old (1981) ARRL handbook. It is a DC receiver, looks like alot of fun, but it isn't fun now. Here is the problem. 1) No oscillation! I can't find it (the VFO) on my DX-398 receiver at all, or on my Radio Shack freq counter. 2) The power (+ side) electrolytic is supposed to be a 500uF, 16 volt. I am using a 470uF 35 volt. It gets really hot!! Short somewhere?!?!?! The VFO is REALLY simple, it has one transistor and about 7 other parts. I can't seem to see what is wrong, and I have tried. I would sure appreciate some Elmer'ing here! ANY help would be much appreciated. I have the above mentioned tools at my command, a multimeter, and an old Heathkit "scope. (which I really don't know how to use. If you happened to insert the diodes in the fullwave rectifier reversed, you will have negative voltage at the input of your filter instead of positive voltage, and the input filter cap will conduct, and get hot (in a fullwave rectifier supply). If that happens you hope the filter cap DID short the supply to ground instead of passing the reverse polarized voltage on to other solid state devices! In time this will be rough on your transformer, too. You might want to recheck all the polarities of the diodes. Dick |
The only time I have seen caps get hot is when they are in backwards. If
there is too much ripple voltage, the cap can get warm. I would double check the wiring. I am not sure what method you used to make the VFO, so everything is up in the air. Pete Active8 wrote in message ... In article , says... "TC Dufresne" wrote in : Hi: I am having a problem with a "Simple Receiver for Beginners". It is from a design that was featured in an old (1981) ARRL handbook. It is a DC receiver, looks like alot of fun, but it isn't fun now. Here is the problem. 1) No oscillation! I can't find it (the VFO) on my DX-398 receiver at all, or on my Radio Shack freq counter. 2) The power (+ side) electrolytic is supposed to be a 500uF, 16 volt. I am using a 470uF 35 volt. It gets really hot!! Short somewhere?!?!?! The VFO is REALLY simple, it has one transistor and about 7 other parts. I can't seem to see what is wrong, and I have tried. I would sure appreciate some Elmer'ing here! ANY help would be much appreciated. I have the above mentioned tools at my command, a multimeter, and an old Heathkit "scope. (which I really don't know how to use. Any chance? Thanks in advance, Tom KCØGXX Gotta be a short somewhere. Filter caps ain't supposed to get hot, and yours is over rated to begin with. and when you run an electrolytic at a different WVDC than it's rated at, you can't be sure the capacitance is the same as marked on the can. but it should still filter and not get hot. you'd think something else would heat up if there was a short. should draw excessive current. unless it blew something and is now an open, then the cap shouldn't get hot any more. |
Everyone. I fixed the VFO. Its a good news/bad news thing.
Apparently my MPF102, the heart of the VFO, was either shorted out or not working. I removed it and replaced it with another. Good news..Cool! Now I have a good VFO in my receiver, I can hear it in my trusty DX-398. I adjust the RF coil so its low end (with maximum capacitance on my Hammerland 1-10pF variable capacitor-fully meshed) is around 7.00mHz. When I go to minimum capacitance (no meshed), I hear it only around 7.060mHz. According to specs, I should get a range from 7.00 to 7.2mHz. Why do I not get more range? As far as I know, all caps are up to spec as called for. Do I need to add/subtract capacitance somewhere? Thanks again, Tom |
Everyone. I fixed the VFO. Its a good news/bad news thing.
Apparently my MPF102, the heart of the VFO, was either shorted out or not working. I removed it and replaced it with another. Good news..Cool! Now I have a good VFO in my receiver, I can hear it in my trusty DX-398. I adjust the RF coil so its low end (with maximum capacitance on my Hammerland 1-10pF variable capacitor-fully meshed) is around 7.00mHz. When I go to minimum capacitance (no meshed), I hear it only around 7.060mHz. According to specs, I should get a range from 7.00 to 7.2mHz. Why do I not get more range? As far as I know, all caps are up to spec as called for. Do I need to add/subtract capacitance somewhere? Thanks again, Tom |
"TC Dufresne" wrote in message ... Everyone. I fixed the VFO. Its a good news/bad news thing. Apparently my MPF102, the heart of the VFO, was either shorted out or not working. I removed it and replaced it with another. Good news..Cool! Now I have a good VFO in my receiver, I can hear it in my trusty DX-398. I adjust the RF coil so its low end (with maximum capacitance on my Hammerland 1-10pF variable capacitor-fully meshed) is around 7.00mHz. When I go to minimum capacitance (no meshed), I hear it only around 7.060mHz. According to specs, I should get a range from 7.00 to 7.2mHz. Why do I not get more range? As far as I know, all caps are up to spec as called for. Do I need to add/subtract capacitance somewhere? Tolerances. Try removing a turn from the coil (if it is one you wound) and/or adding some capacitance. Leon -- Leon Heller, G1HSM http://www.geocities.com/leon_heller |
"TC Dufresne" wrote in message ... Everyone. I fixed the VFO. Its a good news/bad news thing. Apparently my MPF102, the heart of the VFO, was either shorted out or not working. I removed it and replaced it with another. Good news..Cool! Now I have a good VFO in my receiver, I can hear it in my trusty DX-398. I adjust the RF coil so its low end (with maximum capacitance on my Hammerland 1-10pF variable capacitor-fully meshed) is around 7.00mHz. When I go to minimum capacitance (no meshed), I hear it only around 7.060mHz. According to specs, I should get a range from 7.00 to 7.2mHz. Why do I not get more range? As far as I know, all caps are up to spec as called for. Do I need to add/subtract capacitance somewhere? Tolerances. Try removing a turn from the coil (if it is one you wound) and/or adding some capacitance. Leon -- Leon Heller, G1HSM http://www.geocities.com/leon_heller |
"TC Dufresne" wrote in message
... Everyone. I fixed the VFO. Its a good news/bad news thing. Apparently my MPF102, the heart of the VFO, was either shorted out or not working. I removed it and replaced it with another. Good news..Cool! Now I have a good VFO in my receiver, I can hear it in my trusty DX-398. I adjust the RF coil so its low end (with maximum capacitance on my Hammerland 1-10pF variable capacitor-fully meshed) is around 7.00mHz. When I go to minimum capacitance (no meshed), I hear it only around 7.060mHz. According to specs, I should get a range from 7.00 to 7.2mHz. Why do I not get more range? As far as I know, all caps are up to spec as called for. Do I need to add/subtract capacitance somewhere? How much did you allow for stray circuit capacitance? |
"TC Dufresne" wrote in message
... Everyone. I fixed the VFO. Its a good news/bad news thing. Apparently my MPF102, the heart of the VFO, was either shorted out or not working. I removed it and replaced it with another. Good news..Cool! Now I have a good VFO in my receiver, I can hear it in my trusty DX-398. I adjust the RF coil so its low end (with maximum capacitance on my Hammerland 1-10pF variable capacitor-fully meshed) is around 7.00mHz. When I go to minimum capacitance (no meshed), I hear it only around 7.060mHz. According to specs, I should get a range from 7.00 to 7.2mHz. Why do I not get more range? As far as I know, all caps are up to spec as called for. Do I need to add/subtract capacitance somewhere? How much did you allow for stray circuit capacitance? |
TC Dufresne wrote:
Good news..Cool! Now I have a good VFO in my receiver, I can hear it in my trusty DX-398. I adjust the RF coil so its low end (with maximum capacitance on my Hammerland 1-10pF variable capacitor-fully meshed) is around 7.00mHz. When I go to minimum capacitance (no meshed), I hear it only around 7.060mHz. According to specs, I should get a range from 7.00 to 7.2mHz. You've probably got more parasitic capacitance in the circuit than that 10 pF represents. That means your capacitance range is more like 41-50 pF (figure picked out of the air) than 1-10 pF. Did the article suggest any special construction techniques to minimize this? -- The function of an asshole is to emit quantities of crap. Spammers do a very good job of that. However, I do object to my inbox being a spammer's toilet bowl. -- Walter Dnes |
| All times are GMT +1. The time now is 10:13 AM. |
Powered by vBulletin® Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
RadioBanter.com