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"Dale J. " wrote in message ...
I doubt it's a parasitic, but if you want to explore that, Measures has his special parasitic kits for sale on his website. Cheers as they say Dale, K9VUJ In article , Skipp can be reached through the sonic server wrote: The grid to cathode short is a clue... You might want to review the parasitic issues with this and similar amplifiers. A parasitic "bang" might be the source of this and or similar problems. Have a look at Rich Measures (ag6k) web page... used to be at http://www.vcnet.com/measures but is now moving (or has moved to) http://www.somis.org There are protections for grid to cathode shorts in 3-500z amps. I like to use a proper triple bypassed grid resistor and have never had grid/cath shorts in any amplifier with said after an upgrade to the parasitic network(s). If you have questions, you can contact me through the sonic server Email icons or review Rich's web page and he will also reply to Emails. cheers and good luck skipp http://sonic.ucdavis.edu : "Chuck \(Jack\) Hawley" wrote: : A friend has an AL80B (bought new) and is on his fourth 3-500 in two years : or so. It just developed a grid-cath short. Supposedly there was a batch of : tubes that were prone to go bad, but the latest ones from MFJ are supposed : to be ok. Apparently not or something is wrong with the amp. He's a good : operator and seems to be tuning and operating within safe limits for the : AL80B. The latest tube is an Amperex as was the first ones in the reported : bad batch. He reduced the filament voltage last time from 5.7 (from the : factory) to about 5 before the present tube was installed. : Any ideas? : Chuck, KE9UW Sorry, but whats so complex about a 1 tube amplifier - if you have an amateur license, you should have the theory to check it out - the procedure for parasitics etc has been in the ARRL handbook for about 30 years or more - a voltmeter can be a useful instrument if its used to check the specifications of the amplifier - and if it is playing up, how do you know its not spraying garbage all across the spectrum? - have you checked? - de VK3BFA Andrew |
"Dale J. " wrote in message ...
I doubt it's a parasitic, but if you want to explore that, Measures has his special parasitic kits for sale on his website. Cheers as they say Dale, K9VUJ In article , Skipp can be reached through the sonic server wrote: The grid to cathode short is a clue... You might want to review the parasitic issues with this and similar amplifiers. A parasitic "bang" might be the source of this and or similar problems. Have a look at Rich Measures (ag6k) web page... used to be at http://www.vcnet.com/measures but is now moving (or has moved to) http://www.somis.org There are protections for grid to cathode shorts in 3-500z amps. I like to use a proper triple bypassed grid resistor and have never had grid/cath shorts in any amplifier with said after an upgrade to the parasitic network(s). If you have questions, you can contact me through the sonic server Email icons or review Rich's web page and he will also reply to Emails. cheers and good luck skipp http://sonic.ucdavis.edu : "Chuck \(Jack\) Hawley" wrote: : A friend has an AL80B (bought new) and is on his fourth 3-500 in two years : or so. It just developed a grid-cath short. Supposedly there was a batch of : tubes that were prone to go bad, but the latest ones from MFJ are supposed : to be ok. Apparently not or something is wrong with the amp. He's a good : operator and seems to be tuning and operating within safe limits for the : AL80B. The latest tube is an Amperex as was the first ones in the reported : bad batch. He reduced the filament voltage last time from 5.7 (from the : factory) to about 5 before the present tube was installed. : Any ideas? : Chuck, KE9UW Sorry, but whats so complex about a 1 tube amplifier - if you have an amateur license, you should have the theory to check it out - the procedure for parasitics etc has been in the ARRL handbook for about 30 years or more - a voltmeter can be a useful instrument if its used to check the specifications of the amplifier - and if it is playing up, how do you know its not spraying garbage all across the spectrum? - have you checked? - de VK3BFA Andrew |
As I mentioned before, a big clue is given in the grid to cathode short
description. It takes a heck of a lot of energy to make these tube elements repeatedly short. A parasitic bang is just such an animal. Rich not only sells the kits cheap, but he provides the information to "roll your own" on his web site. cheers skipp http://sonic.ucdavis.edu : Dale J. wrote: : I doubt it's a parasitic, but if you want to explore that, Measures has : his special parasitic kits for sale on his website. : Cheers as they say : Dale, K9VUJ |
As I mentioned before, a big clue is given in the grid to cathode short
description. It takes a heck of a lot of energy to make these tube elements repeatedly short. A parasitic bang is just such an animal. Rich not only sells the kits cheap, but he provides the information to "roll your own" on his web site. cheers skipp http://sonic.ucdavis.edu : Dale J. wrote: : I doubt it's a parasitic, but if you want to explore that, Measures has : his special parasitic kits for sale on his website. : Cheers as they say : Dale, K9VUJ |
"Voice In Wilderness" wrote in message news:iixYa.30982$ff.20061@fed1read01...
Ah come one guys -- he IS asking for advice as to how to repair the beast. Why give em the old timers drill? 30 years ago many Hams were RF technical by occupation or the military. Things and times have changed -- many are opting for the computer field. Less and less RF savy in the Amateur Radio Service today and that is OK. But when they come on asking for help --- you can Elmer or Bash --- the choice is yours, but you know which one is correct in the spirit of Amateur Radio A refresher course inTHE AMATEURS CODE by Paul M. Segal, W9EEA (1928) The Radio Amateur is: CONSIDERATE..... never knowingly operating in such a way as to lessen the pleasure of others. LOYAL..... offering loyalty, encouragement and support to other amateurs. FRIENDLY..... with slow and patient operation when requested, friendly advice and counsel to the beginner, kindly assistance, co-operation and consideration for the interests of others. These are the hallmarks of the amateur spirit. ------------------------------------------------------------------------- Point taken, and I readily concede that he is asking for help, and hopefully from the replies he will be able to work it out. Three "The Amateur is progressive...He keeps his station abreast of science. It is built well and efficiently. His operating practice is clean and regular" Thats from the 1961 ARRL Handbook - (no paricular year chosen, it was grabbed out of the bookcase at random, and no, I didnt buy it new....) I think its still relevant. It seems to me that this problem has been going on for years - consumed many tubes, and doesnt seem be solved except by "blaming" someone - either MFJ, Eimac, whatever. IF you have an Amateur license and IF you want to operate QRO then there is a commensurate(sp) responsibility to be able to do that WITHOUT causing harmful interference. That is in the terms and conditions of your license. Fair enough, you can pass the exams on crib sheets without any theory - but for heavens sake, this is SUPPOSED to be a technical hobby!. Buy a ARRL handbook, read the section on amplifiers, borrow a scanner and see if its radiating anywhere else - not really high tech stuff, just BASIC rf knowledge that is supposed to be a precondition of getting a license. In the interests of a good argument, de VK3BFA Andrew I get totally ****ed off when 2 amateurs, probably a few hundred miles apart, insist on running QRO on 80m so they can chat to their buddies in armchair comfort - wind the receive RF gain back to eliminate those nasty atmospheric noises, and stuff the rest of the world trying to have a QSO beneath them. |
"Voice In Wilderness" wrote in message news:iixYa.30982$ff.20061@fed1read01...
Ah come one guys -- he IS asking for advice as to how to repair the beast. Why give em the old timers drill? 30 years ago many Hams were RF technical by occupation or the military. Things and times have changed -- many are opting for the computer field. Less and less RF savy in the Amateur Radio Service today and that is OK. But when they come on asking for help --- you can Elmer or Bash --- the choice is yours, but you know which one is correct in the spirit of Amateur Radio A refresher course inTHE AMATEURS CODE by Paul M. Segal, W9EEA (1928) The Radio Amateur is: CONSIDERATE..... never knowingly operating in such a way as to lessen the pleasure of others. LOYAL..... offering loyalty, encouragement and support to other amateurs. FRIENDLY..... with slow and patient operation when requested, friendly advice and counsel to the beginner, kindly assistance, co-operation and consideration for the interests of others. These are the hallmarks of the amateur spirit. ------------------------------------------------------------------------- Point taken, and I readily concede that he is asking for help, and hopefully from the replies he will be able to work it out. Three "The Amateur is progressive...He keeps his station abreast of science. It is built well and efficiently. His operating practice is clean and regular" Thats from the 1961 ARRL Handbook - (no paricular year chosen, it was grabbed out of the bookcase at random, and no, I didnt buy it new....) I think its still relevant. It seems to me that this problem has been going on for years - consumed many tubes, and doesnt seem be solved except by "blaming" someone - either MFJ, Eimac, whatever. IF you have an Amateur license and IF you want to operate QRO then there is a commensurate(sp) responsibility to be able to do that WITHOUT causing harmful interference. That is in the terms and conditions of your license. Fair enough, you can pass the exams on crib sheets without any theory - but for heavens sake, this is SUPPOSED to be a technical hobby!. Buy a ARRL handbook, read the section on amplifiers, borrow a scanner and see if its radiating anywhere else - not really high tech stuff, just BASIC rf knowledge that is supposed to be a precondition of getting a license. In the interests of a good argument, de VK3BFA Andrew I get totally ****ed off when 2 amateurs, probably a few hundred miles apart, insist on running QRO on 80m so they can chat to their buddies in armchair comfort - wind the receive RF gain back to eliminate those nasty atmospheric noises, and stuff the rest of the world trying to have a QSO beneath them. |
In article ,
Skipp adds a little more wrote: As I mentioned before, a big clue is given in the grid to cathode short description. It takes a heck of a lot of energy to make these tube elements repeatedly short. A parasitic bang is just such an animal. Rich not only sells the kits cheap, but he provides the information to "roll your own" on his web site. cheers skipp http://sonic.ucdavis.edu : Dale J. wrote: : I doubt it's a parasitic, but if you want to explore that, Measures has : his special parasitic kits for sale on his website. : Cheers as they say : Dale, K9VUJ Hows come mine (AL-80A) doent parasite? I don't want to make a big argument of this, but this has frustrated me with this talk of parasites curing all the problems. -- Dale J. Bloomington, Minnesota E-mail: |
In article ,
Skipp adds a little more wrote: As I mentioned before, a big clue is given in the grid to cathode short description. It takes a heck of a lot of energy to make these tube elements repeatedly short. A parasitic bang is just such an animal. Rich not only sells the kits cheap, but he provides the information to "roll your own" on his web site. cheers skipp http://sonic.ucdavis.edu : Dale J. wrote: : I doubt it's a parasitic, but if you want to explore that, Measures has : his special parasitic kits for sale on his website. : Cheers as they say : Dale, K9VUJ Hows come mine (AL-80A) doent parasite? I don't want to make a big argument of this, but this has frustrated me with this talk of parasites curing all the problems. -- Dale J. Bloomington, Minnesota E-mail: |
"Dale J. " wrote in message ...
In article , Skipp adds a little more wrote: As I mentioned before, a big clue is given in the grid to cathode short description. It takes a heck of a lot of energy to make these tube elements repeatedly short. A parasitic bang is just such an animal. Rich not only sells the kits cheap, but he provides the information to "roll your own" on his web site. cheers skipp http://sonic.ucdavis.edu : Dale J. wrote: : I doubt it's a parasitic, but if you want to explore that, Measures has : his special parasitic kits for sale on his website. : Cheers as they say : Dale, K9VUJ Hows come mine (AL-80A) doent parasite? I don't want to make a big argument of this, but this has frustrated me with this talk of parasites curing all the problems. Its been pointed out to me that I have been an unhelpful old grump - and, re-readinfg the Amateurs Code, I can see its true. My aplogies all round - should have engaged brain before opening mouth. Its an interesting fault - have downloaded the MFJ manual and will study it when I have some spare time. However, a few comments in the meantime... 1. If there was a faulty batch of tubes, they would have been cleared out by now - MFJ would have had words with Amperex, so they can be eliminated as future fault causes. 2. is it a design error - possibly, but then again MFJ would be aware of it by now and offered a correction - this company would not stay in business in the Amateur Radio marketplace if it didnt. 3. The filaments high at 5.7 volts - it can be safely assumed that MFJ would have set them up properly at the factory - this suggests that the AC line voltage is high - variations are not unknown (here its plus/minus 10% on 240VAC - fine, except when it causes marginally rated 220V European equipment to die - took me a while to figure that one out....). Check the AC line voltage with a KNOWN ACCURATE voltmeter (I like Fluke, because they come out of the factory set up properly) and adjust transformer taps if necessary. 4. is it a parasitic oscillation - the traditional check is to swing the plate tune capacitor acrtoss its range and check for multiple small dips - if so, there is one. A more scientific way is to use a spectrum analyser if available, a cheap way out there is to sit a scanner near it and tune across every band etc and look for birdies etc. 5. the dynamic bias (good way for QSK switching) and ALC circuit in this thing looks interesting - possibly a fault there (which would explain why the AL80A doesnt have problems - its fixed bias) - but this is speculation, as I said I havent had time to check/compare both circuits or analyse how the AL80B circuit is suppossed to work. Anyway, again my aplogies to the group for being a Grump - will try not to do it again. 73 de VK3BFA Andrew |
"Dale J. " wrote in message ...
In article , Skipp adds a little more wrote: As I mentioned before, a big clue is given in the grid to cathode short description. It takes a heck of a lot of energy to make these tube elements repeatedly short. A parasitic bang is just such an animal. Rich not only sells the kits cheap, but he provides the information to "roll your own" on his web site. cheers skipp http://sonic.ucdavis.edu : Dale J. wrote: : I doubt it's a parasitic, but if you want to explore that, Measures has : his special parasitic kits for sale on his website. : Cheers as they say : Dale, K9VUJ Hows come mine (AL-80A) doent parasite? I don't want to make a big argument of this, but this has frustrated me with this talk of parasites curing all the problems. Its been pointed out to me that I have been an unhelpful old grump - and, re-readinfg the Amateurs Code, I can see its true. My aplogies all round - should have engaged brain before opening mouth. Its an interesting fault - have downloaded the MFJ manual and will study it when I have some spare time. However, a few comments in the meantime... 1. If there was a faulty batch of tubes, they would have been cleared out by now - MFJ would have had words with Amperex, so they can be eliminated as future fault causes. 2. is it a design error - possibly, but then again MFJ would be aware of it by now and offered a correction - this company would not stay in business in the Amateur Radio marketplace if it didnt. 3. The filaments high at 5.7 volts - it can be safely assumed that MFJ would have set them up properly at the factory - this suggests that the AC line voltage is high - variations are not unknown (here its plus/minus 10% on 240VAC - fine, except when it causes marginally rated 220V European equipment to die - took me a while to figure that one out....). Check the AC line voltage with a KNOWN ACCURATE voltmeter (I like Fluke, because they come out of the factory set up properly) and adjust transformer taps if necessary. 4. is it a parasitic oscillation - the traditional check is to swing the plate tune capacitor acrtoss its range and check for multiple small dips - if so, there is one. A more scientific way is to use a spectrum analyser if available, a cheap way out there is to sit a scanner near it and tune across every band etc and look for birdies etc. 5. the dynamic bias (good way for QSK switching) and ALC circuit in this thing looks interesting - possibly a fault there (which would explain why the AL80A doesnt have problems - its fixed bias) - but this is speculation, as I said I havent had time to check/compare both circuits or analyse how the AL80B circuit is suppossed to work. Anyway, again my aplogies to the group for being a Grump - will try not to do it again. 73 de VK3BFA Andrew |
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