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Hey, all. First--I have been having a great time with my QDX. I've made numerous FT8 and JS8 contacts. I've even worked with other FSK modes with this little transmitter. I built mine for 9VDC input and I am seeing 5W on 80, 40, and 30 meters. I sometimes see between 5.3 and 5.6 on 40M. I am getting 3.8W on 20 meters.
So, Right when I was working an FT8 QSO, I heard what sounded like a crack sound from inside the QDX enclosure. Then, the smell. I knew then something went terribly wrong. I found the cracked BS170 as soon as I pulled the board out of the enclosure. I'm in the process of buying new BS170s. I know it is a TO-92 style, but I am seeing other variants of the transistor: D26Z, D74Z, etc. I have three questions:
1) Is there a specific BS170 I should get or will any of them work provided it's a TO-92?
2) Is there anything else I should do to prevent another BS170 fail?
3) Has anyone found an alternative to the BS170 that has less potential for failure?
Thanks,
Wayne KB4DSF
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Hi Wayne.
And was the failure also on 40? That sounds like there is something intermittent maybe, on your 40m antenna. So the SWR will also be fluctuating...not good!
Roger
8P6RX
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On 29/08/2023 07:55, Wayne Greene wrote: I sometimes see between 5.3 and 5.6 on 40M.
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Wayne,
Are you using any kind of antenna tuner?
I think using a manual tuner with a switchable SWR indicator is a good way to prevent future BS170 failures.
Good luck with the repairs!
--Al
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Hey, Roger. I've not noticed any SWR fluctuations, but you bring up a good point. I might have to watch that more closely when I repair the radio.
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Hey, Al, but I will admit, it's not one specific for QRP. It's my shack's auto tuner. That might not be the best choice.
Wayne
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Wayne,
Thanks for the reply!?
Read over other posts here about use of auto-tuners and the Q-Line. In some cases they'll show a momentary high VSWR to your rig. The PA in QCX-QDX-QMX doesn't like too high a VSWR and could stress one or more BS-170s leading to a failure.
The "Tayloe/LED/SWR-bridge" at least will give you a fighting chance.
Welcome to the club!
--Al
WD4AH
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Or put an absorptive bridge between the QxX and switch it in for tuning, then out to operate. Also don't let the tuner auto tune when it detects a change in SWR.?
--
73, Dan? NM3A
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Hi Wayne,
To answer question 3… there is a better transistor for replacing the BS170’s - TN0606. The data sheet can be found here:
Note that the source and drain pins are reversed from the BS170 so you’d flip the TN0606 upside down (flat side against the washer). Others have made this substitution with excellent results. Again, it’s a good idea to place a very thin layer of thermal grease on both sides of the transistors to maximize heat transfer to the board.
Hope this helps!
Tony - AC9QY
Hey, all. First--I have been having a great time with my QDX. I've made numerous FT8 and JS8 contacts. I've even worked with other FSK modes with this little transmitter. I built mine for 9VDC input and I am seeing 5W on 80, 40, and 30 meters. I sometimes see between 5.3 and 5.6 on 40M. I am getting 3.8W on 20 meters.
So, Right when I was working an FT8 QSO, I heard what sounded like a crack sound from inside the QDX enclosure. Then, the smell. I knew then something went terribly wrong. I found the cracked BS170 as soon as I pulled the board out of the enclosure. I'm in the process of buying new BS170s. I know it is a TO-92 style, but I am seeing other variants of the transistor: D26Z, D74Z, etc. I have three questions:
1) Is there a specific BS170 I should get or will any of them work provided it's a TO-92?
2) Is there anything else I should do to prevent another BS170 fail?
3) Has anyone found an alternative to the BS170 that has less potential for failure?
Thanks,
Wayne KB4DSF
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Wow! Thank you all for the responses. I'm thinking I'm going to give the TN0606 a try, and use some thermal grease. Thanks for that hint.
I'm about to expose my real lack of knowledge by asking what might be a dumb question. An SWR bridge provides a 50 ohm impedance to the radio while SWR is read? I that hos that works?
Thanks,
Wayne
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Hi Wayne,
An absorptive bridge uses resistors and a voltage measurement to measure SWR.? The way that it does this puts the worst SWR the TX sees at 2:1.? You need to switch the bridge out once the antenna is tuned.? All of the tuners like this have a toggle switch to do so.
An alternative is an SWR indicator based on the same resistor setup.? Here is one from QRPGuys:
You switch in the resistors until you have a good match, then switch the indicator to Operate.
73
Evan
AC9TU
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I have on of those QRPGuys SWR indicators. I've just not built it, yet. I wonder if I should us that or find and absorptive bridge. I'm planning to use a resonant linked dipole with the QDX when out in the field.
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Evan's answer is correct but misleading
because this is not the sort of SWR bridge that QMX has.
QMX has a Stockton bridge and all it
does is measure the forward and reflected power (or voltage?), By
itself it does nothing to protect you.
If does provide information that can be
used to protect you but AFAIK this needs Hans to write firmware to
do this. It hasn't happened yet.
Chris, G5CTH
On 29/08/2023 19:42, Wayne Greene
wrote:
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I have on of those QRPGuys SWR indicators. I've just not built it,
yet. I wonder if I should us that or find and absorptive bridge.
I'm planning to use a resonant linked dipole with the QDX when out
in the field.
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The QRPGuys SWR indicator uses an absorptive bridge in its design. I use it with my QMX. My problem is that I tend to band hop a lot and I often forget to switch it in for tuning. No problems yet, but one day...
-mike/w1mt
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A resistive bridge, NOT the transformer kind, has 6dB of insertion loss which absorbs much of the reflected power, so the VSWR the transmitter "sees" is ~1.5:1 or less, regardless of what the load is past the bridge.
Because of its loss it is switched in until a tuning solution is found, then switched out to operate.??
73, Don N2VGU
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I have a QRPometer from NM0S. (It was originally a 4SQRP kit, and is now offered by its designer.) It is both a power meter and an SWR meter, and when used as an SWR meter has an absorptive bridge
Link:?
On Tue, Aug 29, 2023 at 2:53?PM mike/w1mt < w1mt.qrp@...> wrote: The QRPGuys SWR indicator uses an absorptive bridge in its design. I use it with my QMX. My problem is that I tend to band hop a lot and I often forget to switch it in for tuning. No problems yet, but one day...
-mike/w1mt
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The TN0606 seems to have a much higher input capacitance than the BS170 and this may translate into slower switching and increased dissipation especially on higher frequencies . ?
Hard to say if they will prove more reliable in that case although the failure modes may be different?
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Thank you. Does anyone know if there is a real difference between the variants of the BS170? I just ordered BS170P mosfets. There were other variants, but I went with this one since it was actually available.?
Wayne
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Lead shape and/or packaging. ? Mike WM4B ?
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From: [email protected] < [email protected]> On Behalf Of Wayne Greene Sent: Tuesday, August 29, 2023 7:04 PM To: [email protected]Subject: Re: [QRPLabs] BS170 Fail ? Thank you. Does anyone know if there is a real difference between the variants of the BS170? I just ordered BS170P mosfets. There were other variants, but I went with this one since it was actually available.?
Wayne
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I ran a TN0106 in my high band QDX for several months and had no issues. I had better output on 10 meters than with the BS170 but nothing dramatically better. I also ran the VN0606 in my low band unit at the same time and also had no issues and performance
was good. Those tests were with otherwise unmodified QDXs. Now I am running with BS170s again but with a 1N4148 commutating diode across L14. On my scope I could see that the spike at end-of-tx was eliminated with this diode.
My original problem was that I fried three sets of BS170 in a few weeks. Every thing seems OK with the diode or when using the TN0106 or VN0606.
What I could see on my scope with the Bs170 as originally designed was a 70 volt spike, presumably discharging L14 at EOT, that was chopped off at 70 volts apparently due to avalanche. It had a wide flat top. With the TN0106 and VN0606 the spike was up to 120
volts but with a narrower flat top. Also avalanche but at a higher voltage level.?
It appears that the TN0106 and VN0606 both avalanche at a level more like a 100 volt transistor and I suspect that the manufacturer (same for both devices) is selecting the 60 volt devices from runs of the 100 volt devices. Not so for the BS170 which avalanche
at a level consistent with a 60 volt device.
Anyway, I think that the diode across? L14 is a better solution than using the TN0106 or VN0606. Yes, both methods work, but why stress the transistors at all? It seems to me that you have more margin with the diode. Likewise for using Zeners, again it probably
works but you are adding two parts instead of one and adding parts on the drains of your PA devices. Also you are discharging L14 through the output transformer winding which seems sub-optimal to me.?
I have an issue in my antenna system where the SWR goes up when it rains. It has been dry recently but we had rain again a couple of nights ago and I made it a point to get on 20 meters where the SWR was up to 2.5 to 1 (antenna impedance here goes low when
it rains btw) and I ran for an hour with no ill effects so my confidence in the diode approach is building.
Just my perspective on this issue. Based on my experiences thus far with QDX and my 48 years as an EE, I would add the diode. It is cheap protection and is situated where it can't really hurt anything. During transmission, the inductor current is basically
DC and so there is no risk of creating spurs. It is only at the end where the current stops that the diode does anything.
73,
Tony
AD0VC
toggle quoted message
Show quoted text
The TN0606 seems to have a much higher input capacitance than the BS170 and this may translate into slower switching and increased dissipation especially on higher frequencies . ?
Hard to say if they will prove more reliable in that case although the failure modes may be different?
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My apologies to the group. I called out the wrong transistor - I meant to spec the TN0106 as a good replacement for the BS170. Thanks Tony for refreshing my memory, it’s been months since John Z and I investigated this and I got confused by references to the VN0606 others have been trying. And thanks to Bruce for flagging the TN0606 as having a much higher input capacitance which led me back to comparing data sheets.
The TN0106 device has a significantly lower turn-on threshold than the BS170 which results in the PA FETs operating closer to saturation and therefore dissipating less power. As a result, more power is transferred to the LPF instead of being wasted as heat. The TN0106 is more compatible with the 5V gate driver than the BS170 which really needs about 6-7V of gate drive to achieve the same level of efficiency.
Tony - AC9QY
On Tue, Aug 29, 2023 at 6:31 PM mux_folder2001 < canthony15@...> wrote:
I ran a TN0106 in my high band QDX for several months and had no issues. I had better output on 10 meters than with the BS170 but nothing dramatically better. I also ran the VN0606 in my low band unit at the same time and also had no issues and performance
was good. Those tests were with otherwise unmodified QDXs. Now I am running with BS170s again but with a 1N4148 commutating diode across L14. On my scope I could see that the spike at end-of-tx was eliminated with this diode.
My original problem was that I fried three sets of BS170 in a few weeks. Every thing seems OK with the diode or when using the TN0106 or VN0606.
What I could see on my scope with the Bs170 as originally designed was a 70 volt spike, presumably discharging L14 at EOT, that was chopped off at 70 volts apparently due to avalanche. It had a wide flat top. With the TN0106 and VN0606 the spike was up to 120
volts but with a narrower flat top. Also avalanche but at a higher voltage level.?
It appears that the TN0106 and VN0606 both avalanche at a level more like a 100 volt transistor and I suspect that the manufacturer (same for both devices) is selecting the 60 volt devices from runs of the 100 volt devices. Not so for the BS170 which avalanche
at a level consistent with a 60 volt device.
Anyway, I think that the diode across? L14 is a better solution than using the TN0106 or VN0606. Yes, both methods work, but why stress the transistors at all? It seems to me that you have more margin with the diode. Likewise for using Zeners, again it probably
works but you are adding two parts instead of one and adding parts on the drains of your PA devices. Also you are discharging L14 through the output transformer winding which seems sub-optimal to me.?
I have an issue in my antenna system where the SWR goes up when it rains. It has been dry recently but we had rain again a couple of nights ago and I made it a point to get on 20 meters where the SWR was up to 2.5 to 1 (antenna impedance here goes low when
it rains btw) and I ran for an hour with no ill effects so my confidence in the diode approach is building.
Just my perspective on this issue. Based on my experiences thus far with QDX and my 48 years as an EE, I would add the diode. It is cheap protection and is situated where it can't really hurt anything. During transmission, the inductor current is basically
DC and so there is no risk of creating spurs. It is only at the end where the current stops that the diode does anything.
73,
Tony
AD0VC
The TN0606 seems to have a much higher input capacitance than the BS170 and this may translate into slower switching and increased dissipation especially on higher frequencies . ?
Hard to say if they will prove more reliable in that case although the failure modes may be different?
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Donald S Brant Jr
Shirley Dulcey KE1L
Bruce Akhurst
Mike Besemer - WM4B