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BITX40 low output power

Jonathan Peakall All Messages By This Member #23134 Hi All, Before I start in with the questions, allow me to introduce myself. Call is KK6RPX and the handle is Jonathan. I live off grid in the middle of nowhere, life long electronics hobbyist. I like to play with everything from tubes to microcontrollers. I have no formal education, just a tinkerer who knows enough to keep his finger off the B+ and can program enough to at least use other peoples code. I just got the BITX40 and the Raduino board. I have managed to check into the West coast Noon Net on 40m today, so it is working. I have subbed a cheap HT microphone in and tried a quicky panadapter connection to a SDR dongle. Fun stuff. I noticed that the output power seemed a little low, so I biased the PA as per instructions. With the bias set to 100mA with PTT down and no audio, when I yell as loudly as I can into the mic I only pull about 840mA, as measured with a Fluke 117. Normal voice level gets 500mA or less. Increasing the bias does not increase output, it stays right around 840mA. The stock mic does exactly the same. Input voltage is 13.8 from a 25 amp supply, so no voltage sag. It does increase slightly at the low end of the band and decrease on the high and as one would expect. Any ideas or is this normal? Another question, I do see mention of increasing the PA voltage but have not found a maximum recommended VIN. While fooling around I was checking the PA heat sink to make sure it wasn't getting too hot. It wasn't, but when I touched it there was a loud pop and a spike in current draw. After looking for bad solder joints and what not I figured out that the bottom of the heat sink had a burr that was cutting into the PCB. I removed the heat sink and filed it down until there were no burrs and I had created enough clearance for a piece of electrical tape underneath. I also added thermal grease to the FET as there was none. Fun little rig, I am very much looking forward to playing with it. All kinds of great mods out there and fun experiments to do.?
John Backo All Messages By This Member #23141 "I noticed that the output power seemed a little low, so I biased the PA as per instructions. With the bias set to 100mA with PTT down and no audio, when I yell as loudly as I can into the mic I only pull about 840mA, as measured with a Fluke 117. Normal voice level gets 500mA or less. Increasing the bias does not increase output, it stays right around 840mA. The stock mic does exactly the same. Input voltage is 13.8 from a 25 amp supply, so no voltage sag. It does increase slightly at the low end of the band and decrease on the high and as one would expect. Any ideas or is this normal?" Jon, every IRF510 is different, Yours is the second instance I have heard of a BITX with a shoutout of about 800 ma. It is probably normal. If you want to get the "normal" 1000 ma. response, you will probably have to change to another IRF510. But these devices are so variable that there is no guarantee the new one will do what you want! If it works, you are probably best advised to leave it alone. Certainly do not exceed 4-4.5v on the gate (even that is iffy for some devices). "Another question, I do see mention of increasing the PA voltage but have not found a maximum recommended VIN." You can easily go to 24v. But (and it is a big but!) you must increase the size of the heatsink about 4-8 times. The No. 1 cause of failure in these devices is heat. They have very poor heat transfer characteristics and a very small die area. All the current that passes through the device goes through this die. If it is too much, it can cause instantaneous failure. Remember to isolate the heatsink from ground as the tab is "hot". And provide the best transfer you can between the IRF510 and the heatsink. Vital to success. (I am sure you have already noticed that). Probably if you are contemplating 48v or so, it can be done -- but you are best advised to change the IRF510 for something heavier, like a IRF520 or 530. Note however, that the input and output circuits will have to be reworked as these devices have considerably different input capacitances. Read KB1GMX and NA5N for nitty-gritty on these MOSFETS. As far as maximum voltage, it should be about 2/3-3/4 of the rated voltage Pk to PK. on the input (AC) side. You would use a corresponding DC voltage to cover that, without exceeding the data sheet values. For the IRF510, the maximum DC voltage drain to source is 70v. But the almost universal recommendation is to not exceed 24v DC. Note that 2x voltage = 4x power. And you are not confined to the IRF series. There are many other excellent MOSFET power devices. Hope this helps. john AD5YE
Jonathan Peakall All Messages By This Member #23145 John, Good information, thanks. I looked in the stash and I happen to have a couple of IRF510's, so I was emboldened to push the PA voltage a little, to 18V. Did see an increase in watts but only when I yell. Talked to a buddy in Nevada (I'm in northern CA) and he only heard a slight difference in my signal and only when I was yelling. So, more than increasing output, I want more mic drive so I don't have to yell, it gets tiresome quickly. Looking at the schematic, could I do something like raising the resistance of R122? Or some other way?? toggle quoted message Show quoted text On Thu, Mar 9, 2017 at 2:37 PM, John Backo via Groups.Io <iam74@...> wrote: "I noticed that the output power seemed a little low, so I biased the PA as per instructions. With the bias set to 100mA with PTT down and no audio, when I yell as loudly as I can into the mic I only pull about 840mA, as measured with a Fluke 117. Normal voice level gets 500mA or less. Increasing the bias does not increase output, it stays right around 840mA. The stock mic does exactly the same. Input voltage is 13.8 from a 25 amp supply, so no voltage sag. It does increase slightly at the low end of the band and decrease on the high and as one would expect. Any ideas or is this normal?" Jon, every IRF510 is different, Yours is the second instance I have heard of a BITX with a shoutout of about 800 ma. It is probably normal. If you want to get the "normal"? 1000 ma. response, you will probably have to change to another IRF510. But these devices are so variable that there is no guarantee the new one will do what you want! If it works, you are probably best advised to leave it alone. Certainly do not exceed 4-4.5v on the gate (even that is iffy for some devices). "Another question, I do see mention of increasing the PA voltage but have not found a maximum recommended VIN." You can easily go to 24v. But (and it is a big but!) you must increase the size of the heatsink about 4-8 times. The No. 1 cause of failure in these devices is heat. They have very poor heat transfer characteristics and a very small die area. All the current that passes through the device goes through this die. If it is too much, it can cause instantaneous failure. Remember to isolate the heatsink from ground as the tab is "hot". And provide the best transfer you can between the IRF510 and the heatsink. Vital to success. (I am sure you have already noticed that). Probably if you are contemplating 48v or so, it can be done -- but you are best advised to change the IRF510 for something heavier, like a IRF520 or 530. Note however, that the input and output circuits will have to be reworked as these devices have considerably different input capacitances. Read KB1GMX and NA5N for nitty-gritty on these MOSFETS.? As far as maximum voltage, it should be about 2/3-3/4 of the rated voltage Pk to PK. on the input (AC) side. You would use a corresponding DC voltage to cover that, without exceeding the data sheet values. For the IRF510, the maximum DC voltage drain to source is 70v. But the almost universal recommendation is to not exceed 24v DC. Note that 2x voltage = 4x power. And you are not confined to the IRF series. There are many other excellent MOSFET power devices. Hope this helps. john AD5YE
Allard PE1NWL All Messages By This Member #23146 I have only 800 mA too when I yell really loud into the mic. But still it gives 6W output at 12V (8W at 13.8V). So should be OK, guess it's just variability of the IRF510 73, Allard PE1NWL toggle quoted message Show quoted text On Thu, March 9, 2017 23:37, John Backo via Groups.Io wrote: "I noticed that the output power seemed a little low, so I biased the PA as per instructions. With the bias set to 100mA with PTT down and no audio, when I yell as loudly as I can into the mic I only pull about 840mA, as measured with a Fluke 117. Normal voice level gets 500mA or less. Increasing the bias does not increase output, it stays right around 840mA. The stock mic does exactly the same. Input voltage is 13.8 from a 25 amp supply, so no voltage sag. It does increase slightly at the low end of the band and decrease on the high and as one would expect. Any ideas or is this normal?" Jon, every IRF510 is different, Yours is the second instance I have heard of a BITX with a shoutout of about 800 ma. It is probably normal. If you want to get the "normal" 1000 ma. response, you will probably have to change to another IRF510. But these devices are so variable that there is no guarantee the new one will do what you want! If it works, you are probably best advised to leave it alone. Certainly do not exceed 4-4.5v on the gate (even that is iffy for some devices). "Another question, I do see mention of increasing the PA voltage but have not found a maximum recommended VIN." You can easily go to 24v. But (and it is a big but!) you must increase the size of the heatsink about 4-8 times. The No. 1 cause of failure in these devices is heat. They have very poor heat transfer characteristics and a very small die area. All the current that passes through the device goes through this die. If it is too much, it can cause instantaneous failure. Remember to isolate the heatsink from ground as the tab is "hot". And provide the best transfer you can between the IRF510 and the heatsink. Vital to success. (I am sure you have already noticed that). Probably if you are contemplating 48v or so, it can be done -- but you are best advised to change the IRF510 for something heavier, like a IRF520 or 530. Note however, that the input and output circuits will have to be reworked as these devices have considerably different input capacitances. Read KB1GMX and NA5N for nitty-gritty on these MOSFETS. As far as maximum voltage, it should be about 2/3-3/4 of the rated voltage Pk to PK. on the input (AC) side. You would use a corresponding DC voltage to cover that, without exceeding the data sheet values. For the IRF510, the maximum DC voltage drain to source is 70v. But the almost universal recommendation is to not exceed 24v DC. Note that 2x voltage = 4x power. And you are not confined to the IRF series. There are many other excellent MOSFET power devices. Hope this helps. john AD5YE
John Backo All Messages By This Member #23148 Jon and Allard. Notice that the input drive to the PA is controlled by R136. Try increasing that SLOWLY and see if it makes a difference. You might also check the AC voltage there. It should be 1-2v Pk to Pk. (maybe a bit more. Not less). That is the AC control of the 2N2219. The voltage to the gate of the final is controlled by RV1. You might also check that. MAKE SURE IT IS 3-4v OR SO. Do NOT increase it at random or fast. You will blow up the final! john AD5YE
Allard PE1NWL All Messages By This Member #23149 Yes I know that R136 is for the drive and it's set correctly in my case. I just wanted to point out that even with only 800 mA max current the PA is still working perfectly fine here - it gives the expected output of 5-7W at 12V, and it's undistorted. I guess that due to variability some IRF's draw more current than other IRF's, and I just happen to have one that draws not so much. It's probably "normal". 73, Allard PE1NWL toggle quoted message Show quoted text On Fri, March 10, 2017 01:14, John Backo via Groups.Io wrote: Jon and Allard. Notice that the input drive to the PA is controlled by R136. Try increasing that SLOWLY and see if it makes a difference. You might also check the AC voltage there. It should be 1-2v Pk to Pk. (maybe a bit more. Not less). That is the AC control of the 2N2219. The voltage to the gate of the final is controlled by RV1. You might also check that. MAKE SURE IT IS 3-4v OR SO. Do NOT increase it at random or fast. You will blow up the final! john AD5YE
Raj vu2zap Member Profile All Messages By This Member #23150 I found an old Motorola junk mic in my collection. It has only 4 leads and has a preamp built in. I don't have to shout but now I have to reduce gain as it sounds like a compressor is on and I can hear my own breathing in the modulation! Raj toggle quoted message Show quoted text At 10/03/2017, you wrote: John, Good information, thanks. I looked in the stash and I happen to have a couple of IRF510's, so I was emboldened to push the PA voltage a little, to 18V. Did see an increase in watts but only when I yell. Talked to a buddy in Nevada (I'm in northern CA) and he only heard a slight difference in my signal and only when I was yelling. So, more than increasing output, I want more mic drive so I don't have to yell, it gets tiresome quickly. Looking at the schematic, could I do something like raising the resistance of R122? Or some other way??
[email protected] All Messages By This Member #23151 Hello raj, is that the gm300 mic? `73 toggle quoted message Show quoted text On Fri, 10 Mar, 2017 at 11:06 am, Raj vu2zap <vu2zap@...> wrote: I found an old Motorola junk mic in my collection. It has only 4 leads and has a preamp built in. I don't have to shout but now I have to reduce gain as it sounds like a compressor is on and I can hear my own breathing in the modulation! Raj At 10/03/2017, you wrote: >John, > >Good information, thanks. I looked in the stash and I happen to have a couple of IRF510's, so I was emboldened to push the PA voltage a little, to 18V. Did see an increase in watts but only when I yell. Talked to a buddy in Nevada (I'm in northern CA) and he only heard a slight difference in my signal and only when I was yelling. > >So, more than increasing output, I want more mic drive so I don't have to yell, it gets tiresome quickly. Looking at the schematic, could I do something like raising the resistance of R122? Or some other way??
Raj vu2zap Member Profile All Messages By This Member #23153 It could be gm300, I have 3 or 4 of these that I bought from a junk dealer. None of the others were easy to use. This one the printing on the back has faded, I'll try and see if I can somehow decipher it next week when I am back in town. Raj At 10/03/2017, you wrote: toggle quoted message Show quoted text Hello raj, is that the gm300 mic? `73 On Fri, 10 Mar, 2017 at 11:06 am, Raj vu2zap <vu2zap@...> wrote: I found an old Motorola junk mic in my collection. It has only 4 leads and has a preamp built in. I don't have to shout but now I have to reduce gain as it sounds like a compressor is on and I can hear my own breathing in the modulation! Raj
[email protected] All Messages By This Member #23154 Thanks Raj,, hopefully you can share schematic if there`s a modification you`ve made in the Mic,,i would like to try for my gm300 mic,, `73 toggle quoted message Show quoted text On Fri, 10 Mar, 2017 at 2:37 pm, Raj vu2zap <vu2zap@...> wrote: It could be gm300, I have 3 or 4 of these that I bought from a junk dealer. None of the others were easy to use. This one the printing on the back has faded, I'll try and see if I can somehow decipher it next week when I am back in town. Raj At 10/03/2017, you wrote: Hello raj, is that the gm300 mic? `73 On Fri, 10 Mar, 2017 at 11:06 am, Raj vu2zap <vu2zap@...> wrote: I found an old Motorola junk mic in my collection. It has only 4 leads and has a preamp built in. I don't have to shout but now I have to reduce gain as it sounds like a compressor is on and I can hear my own breathing in the modulation! Raj
Raj vu2zap Member Profile All Messages By This Member #23159 Dwine, If your RJ connector has just 4 wires crimped then you can probably use it. If you open the mic then you will figure out the colors, I can tell you only after next monday when I am back in town. I did not make any mods to it. I used it as is. I desoldered a RJ LAN connector from a blown router and used that. Cheers Raj Maybe this one from repeater builder, go by the colors in the RJ jack. At 10/03/2017, you wrote: toggle quoted message Show quoted text Thanks Raj,, hopefully you can share schematic if there`s a modification you`ve made in the Mic,,i would like to try for my gm300 mic,, `73 On Fri, 10 Mar, 2017 at 2:37 pm, Raj vu2zap <vu2zap@...> wrote: It could be gm300, I have 3 or 4 of these that I bought from a junk dealer. None of the others were easy to use. This one the printing on the back has faded, I'll try and see if I can somehow decipher it next week when I am back in town. Raj At 10/03/2017, you wrote: Hello raj, is that the gm300 mic? `73 On Fri, 10 Mar, 2017 at 11:06 am, Raj vu2zap <vu2zap@...> wrote: I found an old Motorola junk mic in my collection. It has only 4 leads and has a preamp built in. I don't have to shout but now I have to reduce gain as it sounds like a compressor is on and I can hear my own breathing in the modulation! Raj
Jonathan Peakall All Messages By This Member #23165 John, OK, so I played around with R136 and then readjusted RV1. With R136 fully cranked I can get almost 1 amp draw when yelling and about 750mA in a reasonable voice level. Doesn't seem to be driving the FET too hard, I gave it a test for a few minutes and the heat sink was barely warm. Raj, sounds like a preamp works for you. What about something like this: Thanks for the help folks! I can see this thing is going to be a time sink.....
Raj vu2zap Member Profile All Messages By This Member #23167 Looks good, It could be with less components but go for it as is and see what you get! Raj At 10/03/2017, you wrote: toggle quoted message Show quoted text Raj, sounds like a preamp works for you. What about something like this:
Jerry Gaffke All Messages By This Member #23168 Hard to imagine much simpler. ?I'd try to figure out how to add a component: a mike gain pot. ?Maybe a 10k pot to ground between stages, keep the existing DC blocking caps before and after the pot. ?R121 in the existing Bitx40 is no longer necessary with this new stage in front, but R121 would not do any harm. ?R1 of the new stage might want to be 47k like R121 was in the Bitx40, since we're running from 12v, not 3v. toggle quoted message Show quoted text On Fri, Mar 10, 2017 at 06:29 am, Raj vu2zap wrote: Looks good, It could be with less components but go for it as is and see what you get! ?
Raj vu2zap Member Profile All Messages By This Member #23200 I would remove the collector R and C and connect direct to bitx. Some value changes may be needed. At 10/03/2017, you wrote: toggle quoted message Show quoted text Hard to imagine much simpler.? I'd try to figure out how to add a component: a mike gain pot.? Maybe a 10k pot to ground between stages, keep the existing DC blocking caps before and after the pot.? R121 in the existing Bitx40 is no longer necessary with this new stage in front, but R121 would not do any harm.? R1 of the new stage might want to be 47k like R121 was in the Bitx40, since we're running from 12v, not 3v. On Fri, Mar 10, 2017 at 06:29 am, Raj vu2zap wrote: Looks good, It could be with less components but go for it as is and see what you get!

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