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[SPAM] Re: [SPAM] Re: [BITX20] IRF510 amplifier failures

K9HZ All Messages By This Member #40625 开云体育 Now with this said… you could measure the current draw to the FET using a small Hall-effect device and use that to make a simple resettable trip circuit.? Very easy to do. ? ? Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ ? Owner - Operator Big Signal Ranch – K9ZC Staunton, Illinois ? Owner – Operator Villa Grand Piton – J68HZ Soufriere, St. Lucia W.I. Rent it: *Like us on Facebook!* ? ? email:? bill@... ? toggle quoted message Show quoted text From: [email protected] [mailto:[email protected]] On Behalf Of K9HZ Sent: Monday, January 29, 2018 9:42 AM To: [email protected] Subject: [SPAM] Re: [SPAM] Re: [BITX20] IRF510 amplifier failures ? I think you are missing the point.? Tim is somewhat correct in that limiting the current to the FETs at any point along the characteristic operational curve in any form causes non-linearity and distortion because of it.? It’s more akin to flat-topping although maybe not as sharp.? In any case, it’s not what you want to do. ? ? Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ ? Owner - Operator Big Signal Ranch – K9ZC Staunton, Illinois ? Owner – Operator Villa Grand Piton – J68HZ Soufriere, St. Lucia W.I. Rent it: *Like us on Facebook!* ? ? email:? bill@... ? From: [email protected] [mailto:[email protected]] On Behalf Of Arv Evans Sent: Monday, January 29, 2018 1:44 AM To: [email protected] Subject: [SPAM] Re: [BITX20] IRF510 amplifier failures ? Tim AB0WR No modulation involved.? The operation is as a switch between ON and almost OFF.? Gain of the two BJTs makes it operate quickly and drop the output voltage to the point where the current sensing resistor has less than the 0.65 threshold voltage across its base-emitter junction. I see where it does look like some of the CB-era AM modulators because it causes a drop in voltage when current exceeds the base-emitter threshold.? ? ? I'm still looking at the current limiter with an eye toward possibly adding another MOSFET to get both polarity protection and current limiting.? Problem with fuses for protection is that most do not operate fast enough.? There are specialty Fast-Acting fuses? and Slow-Blow fuses but most hams do not have a ready stock of these. ? Arv _._ ? On Sun, Jan 28, 2018 at 9:59 PM, Tim Gorman <tgorman2@...> wrote: It would seem to me that this type of operation is actually AM modulation of final. When you limit the current flow in an FET that is very similar to plate modulation in a vacuum tube. It certainly can't be good for the linearity of the amplifier since the operational curve would no longer be linear but, instead, flat-topped at some value. Why not just fuse the power lead? It would tell you immediately that you have a problem. tim ab0wr On Sat, 27 Jan 2018 12:13:49 -0800 "Arv Evans" <arvid.evans@...> wrote: > Hello > > Still thinking about IRF510 failures and ways to avoid making > smoke..... > > It seems that there may be two ways to limit current in BITX RF PA > stages that use the IRF510 device.? First would be to incorporate a > current limiter in the positive voltage supply to the RF PA stage. > Second might be to use current sensing in the RF PA supply line to > cause a voltage drop in the MOSFET bias line(s).? > > In the first instance it should be possible to use another IRF510 or > preferably a higher power, MOSFET as a control that limits voltage to > the RF PA section if the current exceeds a preset value (usually this > would be 2.0 to 3.0 amperes).? > > This circuit has not been built or tested by me (too cold in Idaho > hamshack in winter). The MOSFET could be an IRF840, or similar. > Option-B? potentially solves another problem, that of low level noise > from powered RF PA stage during receive mode.? > > In the second instance we could get by with smaller control devices > if we used current sensing in the RF PA power line to turn off bias > to the IRF510 device(s).? > > This bias control circuit used by AC2CZ in his 50 watt IRF510 linear > ( ).? You could probably > do this using 2N3906 transistors.? I like the fact that it includes a > warning light/LED. > > Arv? K7HKL > _._ ?
Leland Lannoye All Messages By This Member #40626 开云体育 Is there a circuit or, better yet, a board available? It sounds like this could be current limiting as well. Sent from my Verizon, Samsung Galaxy smartphone toggle quoted message Show quoted text -------- Original message -------- From: K9HZ <bill@...> Date: 1/29/18 08:58 (GMT-05:00) To: [email protected] Subject: Re: [SPAM] Re: [SPAM] Re: [BITX20] IRF510 amplifier failures Now with this said… you could measure the current draw to the FET using a small Hall-effect device and use that to make a simple resettable trip circuit.? Very easy to do. ? ? Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ ? Owner - Operator Big Signal Ranch – K9ZC Staunton, Illinois ? Owner – Operator Villa Grand Piton – J68HZ Soufriere, St. Lucia W.I. Rent it: *Like us on Facebook!* ? ? email:? bill@... ? From: [email protected] [mailto:[email protected]] On Behalf Of K9HZ Sent: Monday, January 29, 2018 9:42 AM To: [email protected] Subject: [SPAM] Re: [SPAM] Re: [BITX20] IRF510 amplifier failures ? I think you are missing the point.? Tim is somewhat correct in that limiting the current to the FETs at any point along the characteristic operational curve in any form causes non-linearity and distortion because of it.? It’s more akin to flat-topping although maybe not as sharp.? In any case, it’s not what you want to do. ? ? Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ ? Owner - Operator Big Signal Ranch – K9ZC Staunton, Illinois ? Owner – Operator Villa Grand Piton – J68HZ Soufriere, St. Lucia W.I. Rent it: *Like us on Facebook!* ? ? email:? bill@... ? From: [email protected] [mailto:[email protected]] On Behalf Of Arv Evans Sent: Monday, January 29, 2018 1:44 AM To: [email protected] Subject: [SPAM] Re: [BITX20] IRF510 amplifier failures ? Tim AB0WR No modulation involved.? The operation is as a switch between ON and almost OFF.? Gain of the two BJTs makes it operate quickly and drop the output voltage to the point where the current sensing resistor has less than the 0.65 threshold voltage across its base-emitter junction. I see where it does look like some of the CB-era AM modulators because it causes a drop in voltage when current exceeds the base-emitter threshold.? ? ? I'm still looking at the current limiter with an eye toward possibly adding another MOSFET to get both polarity protection and current limiting.? Problem with fuses for protection is that most do not operate fast enough.? There are specialty Fast-Acting fuses? and Slow-Blow fuses but most hams do not have a ready stock of these. ? Arv _._ ? On Sun, Jan 28, 2018 at 9:59 PM, Tim Gorman <tgorman2@...> wrote: It would seem to me that this type of operation is actually AM modulation of final. When you limit the current flow in an FET that is very similar to plate modulation in a vacuum tube. It certainly can't be good for the linearity of the amplifier since the operational curve would no longer be linear but, instead, flat-topped at some value. Why not just fuse the power lead? It would tell you immediately that you have a problem. tim ab0wr On Sat, 27 Jan 2018 12:13:49 -0800 "Arv Evans" <arvid.evans@...> wrote: > Hello > > Still thinking about IRF510 failures and ways to avoid making > smoke..... > > It seems that there may be two ways to limit current in BITX RF PA > stages that use the IRF510 device.? First would be to incorporate a > current limiter in the positive voltage supply to the RF PA stage. > Second might be to use current sensing in the RF PA supply line to > cause a voltage drop in the MOSFET bias line(s).? > > In the first instance it should be possible to use another IRF510 or > preferably a higher power, MOSFET as a control that limits voltage to > the RF PA section if the current exceeds a preset value (usually this > would be 2.0 to 3.0 amperes).? > > This circuit has not been built or tested by me (too cold in Idaho > hamshack in winter). The MOSFET could be an IRF840, or similar. > Option-B? potentially solves another problem, that of low level noise > from powered RF PA stage during receive mode.? > > In the second instance we could get by with smaller control devices > if we used current sensing in the RF PA power line to turn off bias > to the IRF510 device(s).? > > This bias control circuit used by AC2CZ in his 50 watt IRF510 linear > ( ).? You could probably > do this using 2N3906 transistors.? I like the fact that it includes a > warning light/LED. > > Arv? K7HKL > _._ ?

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