Date   
Re: BITX QSO Afternoon/Night, Sunday, January 28, 3PM/7PM Local Time, 7277 kHz in North America, 7177 kHz elsewhere

ekelley
 

Look for us in the mid-west to be on 7278 the other frequency is too close to the 7275
traffic that is on every Sunday.

On 1/25/2018 1:34 PM, John P wrote:
BITX QSO Afternoon/Evening, Sunday, January 28, 3PM & 7PM Local Time, 7277 kHz in North America, 7177 kHz elsewhere.

While not the greatest band conditions, the afternoon session last week was better than the evening session! So hopefully, we can try both times again this week.

Join us as we make contacts from BITX40 to BITX40 on 7.277 MHz in 40 meters!

This is a worldwide event for BITX40 stations starting at 7pm in each time zone. To participate, call CQ BITX on Sunday, starting at 3PM and/or 7PM your local time. The BITX QSO Night continues through the evening and conditions usually improve after sunset, so it is worthwhile to participate later in the evening.

Suggested Best Operating Practices:

Work at QRP power levels unless conditions require more power.
Call and listen for CQ BITX on the hour and every quarter hour.
It is helpful if you call CQ BITX with your callsign, name and location. 
Repeat your callsign a number of times during your CQ BITX and during QSO's.
Start a QSO by confirming the callsign, location, name and signal report of the other operator.
Say the callsign, name and location of the other operator so others can hear.
If the frequency is busy, avoid long conversations.
After your initial QSO is complete, ask if there are any other stations who would like to contact.

Report your QSO's, discuss propagation, noise, signal reports, audio reports, antenna type, etc. in this thread.

This is an undirected, scheduled event.  The BITX QSO Night relies on you to call CQ BITX to initiate contacts with other stations, so warm up that final and transmit a few calls on Sunday evening.  Talk to you then!
--
John - WA2FZW


Re: Something has been blown

KC9SGV <kc9sgv@...>
 

Cesar,
Those Mosfets are really cheap on eBay...
Get a handful....
I did.

Bernie,
KC9SGV
Chicago

Sent from my iPad

On Jan 25, 2018, at 2:48 PM, César EA3IAV <Cesarleon@...> wrote:

<A713F7E8_C6D7_471C_A728_141FF07B8525.jpeg><16F70DE6_396F_47AA_9F38_CC4CC3B8E7A8.jpeg><9B9D5551_AC32_441C_B1E6_A5C862D29063.jpeg><70C5A1C8_DB48_4535_B786_60FE4E8A568F.jpeg>Yesterday I installed everything and it worked fine...
Today I put everything in the box and decided to use the case as heatsink. I put insulator and thermal silicone. Ok i turned it on and there has been a little explosion and smoke in the area of the transistors. I don’t see anything blown... 
maybe i blew the transitors? How can I check? I did tested that there was no continuity between the metal thing of the transistor and the screw! 
Hell i hate this!

now after removing the transistors from the case it turns on normally 

Re: SMD Group Build

Jack, W8TEE
 

Great idea on the tool. Might have to make one of those!

Jack, W8TEE



From: Ken KM4NFQ <km4nfq@...>
To: BITX20@groups.io
Sent: Thursday, January 25, 2018 4:39 PM
Subject: Re: [BITX20] SMD Group Build

Hello Jack, W8TEE,

The Revolving LED SMD Practice Kit was my introduction to soldering SMDs.
So it was also my introduction to a Solder Paste Syringe, and application needles.
I have a heavy thumb (ham-fisted, I am).
A gentle squeeze on the syringe produced an on-going stream of solder paste.
I thought it would never stop coming out!
Another thing is, the needle was a mess to clean up afterwards.
I used a Q-Tip and a wire to clean it up as best as I could.
So my first experience kind of soured me on using the needle applicator.
I wanted more control over how much solder paste came out of the syringe.
So what I did was to make a screw-controlled applicator.
I don't use the needles at all. The solder paste comes out very slowly.
As it comes out, I use a pointed dental tool to get a small gob on the point.
Then I apply it to a pad with the dental tool.
Every once in awhile I give the screw a slight twist.
This works great for ME. YMMV.






There is a cap that screws over the end of the syringe, which I replace when I finish applying solder paste.
The scrap-wood prototype worked so well, I never made a finished product.
I call this tool my Solder Paster Extruder.

I found my 'Reflow Oven' at the Goodwill Store (re-purposed Toaster Oven).


I calibrated it with an old kitchen oven thermometer which is accurate.
I made marks on the dial, then checked the temperature for each mark.
In actual use, I turn it to my 3rd mark and wait for the temperature to get to 200degF.
Then I turn it to my 6th mark, and the temperature goes to 350degF.
I turn the oven off, open the door, and let the PCB cool down.

I got my SMD Tweezers, and Hot Air Gun, from eBay, as well as the SMD Practice Kit.
Since then, I have sourced 0805 SMD resistors, capacitors, and ICs from Mouser.
Most of the other tools I already had in my studio.

Regards,
Ken, KM4NFQ






On Thu, Jan 25, 2018 at 9:57 AM, Jack Purdum via Groups.Io <jjpurdum@...> wrote:
Mornin' Ken:

You're right, and I may have glossed over this idea too quickly. This might be a great way to get them to try at low expense and without insulting their fabrication abilities. I do have everything you suggested except the skillet. That might be the club's next project after the frequency counter.

Jack, W8TEE



From: Ken KM4NFQ <km4nfq@...>
To: BITX20@groups.io
Sent: Thursday, January 25, 2018 6:24 AM
Subject: Re: [BITX20] SMD Group Build

Hello Jack, W8TEE,

The SMD components are not the only thing that you might need.
Also look into:
Solder paste in a syringe with application needles (~ $20+ for 35gm)
Toaster Oven or Electric Skillet for melting the solder onto the PCB (find in a thrift store)
Tweezers (for manually placing the components)
Hot Air Gun (for removing parts)
Magnifying Loupe (for inspecting your work)
Desoldering wick (removing solder bridges from ICs)
Soldering Iron with fine tip (rework tombstoned parts)

The revolving LED kit is a challenge to build for beginners.
$3 - $4 per person in the group. All the components are in the kit.
The circuit itself is in the middle of the PCB.
But there are three columns of practice components on each side.
1206, 0805, 0805, 0603, 0603, and 0402 sizes are included, so you get an idea.
The practice columns are not connected to the revolving LED circuit.
The revolving LED circuit has a 555 and a CMOS 4017, as well as
transistors, diodes, and LEDs, so you get a variety of SMDs to work with.

In my recent and limited experience, making an SMD project consists of:
Identifying the components.
Applying solder paste evenly to the pads.
Placing the SMD components on the solder paste.
All the components are soldered at once.
Clean the flux from around the components (Isopropyl Alcohol & toothbrush)
Smoke test.
Only part of my circuit worked, but I got some SMD soldering practice for $3 - $4.

Regards,
Ken, KM4NFQ






On Wed, Jan 24, 2018 at 8:27 PM, Jack Purdum via Groups.Io <jjpurdum@...> wrote:
All:

We have a small group of local hams who enjoy building stuff, yet most are scared to death of SMD parts. Our last build had 29 do the build which is about half of our group. What I'd like to do is put together a small SMD project and have 30 or so boards made. (I have no idea what a good starter project would be.) If anyone has done this, are the board costs less than thru-holes boards? Also, are Mouser and Digikey the likely source for large (e.g., 1206) parts or do you know of a better source.

Thanks!

Jack, W8TEE






Re: Something has been blown

Arv Evans
 

César EA3IA

Since there is no short with the IRF-510 devices in place but not connected to the chassis, it is 
possible that the antenna was disconnected, shorted, or some other anomaly.  Unfortunately
MOSFETs used as RF power amplifiers tend to self-destruct if the load is not of proper
impedance.  Too low an impedance and they will overheat, and too high an impedance and
they will go into oscillation and destroy themselves with high current. 

As Bernie KC9SGV has suggested replacement devices are relatively inexpensive from Ebay
vendors.  Some will probably raise the issue of Ebay sourced parts being less than perfect
but I have been using Ebay sourced IRF-510's for over 10 years with no problems. 

Safest way to bring a new BITX on-line is to use a known good dummy load.  Once you have
verified it is working properly you can connect it to your antenna via an ATU and apply only a
little amount of audio to generate a low output power while you tune the ATU for as close as
you can get to a 50 ohm match.  Once you have a good match between BITX and antenna
you can then apply normal audio or full CW power. 

It would be nice if there were a way to make the IRF-510 devices immune to impedance
mis-match problems, but to-date that does not seem to be available. 

Arv  K7HKL
_._

Re: Analog keyer revisited #ubitx

Mike Woods
 

John

I like this solution and I hope to give it a try out this weekend.

Mike ZL1AXG

On 26/01/18 9:38 AM, John Pieper wrote:
I incorporated the keyer code from W0EB and W2CTX into my personal software build, but being determined to save the last analog input for S/power metering, kept the single input that detects three levels (four originally, but I don't care much about straight keying so I left that out for now). Some of the errors I've experienced and others have reported with the single line seemed to me consistent with the ADC deciding the state was "both" instead of "dit", for example an 'I' becoming an 'N' while the dit paddle is held closed. Looking at the nominal voltage levels with the provided resistors, I saw that there was only around 0.22 volts between the "dit" and "both" levels (1.60 vs 1.38 V). On the other hand, there is 1.8 volts between "dit" and "dah". Errors due to fluctuations would be much more likely between "dit" and "both".

Hoping to improve the situation, I did a little numerical study of the divider circuit. It turned out that there is really no area in the 2D "space" of possible resistor values that gives an ideal result (large equal intervals between both pairs of levels), but it is possible at least to increase the dit-both spacing significantly, at the expense of the dit-dah spacing. In the end I replaced the 2.2k resistor with a 5.1k one. Now the nominal levels are 3.4 V for "dah", 2.6 V for "dit", and 2.1 V for "both". I made an educated estimate of what the boundary ADC values should be and put them into my customized paddle-latch function.

The results so far are favorable. I have sent a fair amount of practice code (I also added a "practice" mode that only plays the sidetone) at speeds up to 25 wpm, and have detected no errors that were not caused by my fist. The iambic action seems flawless and smooth. I might actually get good at sending iambic style someday...

73, John AD0RW


--
Mike Woods
mhwoods@...

Re: End whistling into the mic

Paul Smith
 

Go to http://www.audiocheck.net/index.php and download a 1kHz pure sine test file via your soundcard. Free... I use it a lot for testing here.

Solder Paste Extruder

Arv Evans
 

Ken, KM4NFQ

That solder paste extruder is a great idea.  I have used these tubes of solder paste for
several years but always fought with expressing enough, but not too much, of the paste.

Tomorrow I will be in my workshop building one of your devices.  I really like the concept.

It seems possible that the solder paste extruder could also be adapted to a CNC Mill
or a 3D printer and used with appropriate G-Code to place small solder paste dots
for oven-baking of components to the PCB. 

Arv  K7HKL
_._

ARROW Bus to Hamvention

John Wasciuk
 

January 26, 2018
 
2878 Ticknor Ct
Ann Arbor, MI 48104-6921
 
Dear Fellow Radio Amateurs & Friends of ARROW Communication Association,

Once again, this year, The ARROW Communication Association of Ann Arbor, Michigan is sponsoring its annual round-trip by bus to Hamvention on Saturday, May 19, 2018. Details are at:


This trip has run since 2002. We have sold out the last four years! We have had riders come from all over. They have come from Kalamazoo and Grand Rapids. In 2017, John, VE3IPS came down from Toronto to be with us. You can see some fine photos and a great video on his web site:


As in any endeavor of this kind, we appreciate any additional positive word to be spread around via web pages, news letters and on the air!

For $65.00 ($55.00 before April 1), we offer a free continental breakfast, space at our flea market table and, most of all, PRIZES! It is probably complete coincidence, but a number of the products we have been given have then made it into the Product Review column of QST (QRP Labs, QRPme and Borden Radio Company come to mind).

I am putting this email on a number of blogs and email lists for the benefit of our donors. While the bus may be local or regional, our sponsors sell internationally. ARROW would like to return their generosity with a bit of publicity.

If it is all right with the moderator of this list, we’d like to post another email when we are farther along with our 2018 campaign. We try to list our sponsors and a bit about them and the package they have sent for our lucky passengers.

A list of previous donors can be seen below.

We thank you all for your kind attention. We look forward to seeing you at Hamvention and on the bus!

73,

John F. Wasciuk
WA8TON / VO1TON / VO1HV
Activities Coordinator,
ARROW Communication Association
Ann Arbor, Michigan
jwasciuk at gmail dot com

List of donors 2014-2017:

Amateur Accessories, Inc
American Radio Supply
American Hakko Products, Inc
Borden Radio Company
Buckmaster International HamCall
Comet Anetnna
Daiwa Meters
Connect Quick (Ironworks Design LLC)
Connect Systems Inc
Debco Electronics
Digi-Key Electronics
DX Engineering
EAE Sales
Elecraft
Far Circuits
Five Dash
Fox Delta
Global TSCM Group Inc KN2C dot US
Ham Radio Outlet
Ham-Sters
HamTestOnline
Heil Sound
Hip Ham Shirts
KB6NW CW Geek (No-Nonsense Study Guides)
Klingenfuss Publications
MCM Electronics
MFJ
Mike’s Electronic Parts
MPD Digital
North Georgia QRP Club
NW Digital Radio
Pacific Antenna QRP Kits
Peebles Originals
QRP Labs
QRPMe
RT Systems
Skilman
Tennadyne Corporation / Cubex Quads
The RF Adapter Guy
Tigertronics
Universal Radio
West Mountain Radio

Re: Something has been blown

Jerry Gaffke
 

If the IRF510's still draw some current through PA-PWR during transmit,
and that current changes when you adjust the gate bias with RV2 and RV3
(adjust this very carefully, as it quickly goes to hundreds of mA)
then the IRF510's are probably just fine.

Regarding cheap IRF510's on ebay, you might read this old thread:
    https://groups.io/g/BITX20/topic/5554568
They cost $1 on mouser for singles, below $0.50 if you buy lots, and you know who made it.
I don't see much point in buying on ebay.

As Arv says, make sure you have a good 50 ohm dummy load when testing.
Perhaps get four Xicon 200 ohm 3W metal film resistors (mouser 283-200-RC)
when buying the spare IRF510's.

Jerry, KE7ER


On Thu, Jan 25, 2018 at 07:31 pm, Arv Evans wrote:
Since there is no short with the IRF-510 devices in place but not connected to the chassis, it is 
possible that the antenna was disconnected, shorted, or some other anomaly.  Unfortunately
MOSFETs used as RF power amplifiers tend to self-destruct if the load is not of proper
impedance.  Too low an impedance and they will overheat, and too high an impedance and
they will go into oscillation and destroy themselves with high current. 

As Bernie KC9SGV has suggested replacement devices are relatively inexpensive from Ebay
vendors.  Some will probably raise the issue of Ebay sourced parts being less than perfect
but I have been using Ebay sourced IRF-510's for over 10 years with no problems. 

Re: Second batch of uBITX shipping? #ubitx

mikael.madsen@...
 

Someone posted that order date 14th december had been shipped but that was some days ago.

Anyone with a later order date later than 14th been informed of shiping yet?

IRF510 amplifier failures

Arv Evans
 

Hello

The problem with IRF510 RF amplifiers failing seems to be a recurring one for those who
are not quite careful with antenna matching, bias level, and drive level.  As a way to start
looking into this situation I have performed some on-line searches to see how others are
And there is much more out there to be Google searched and reviewed.

There are a number of potentially useful ideas contained in those articles and discussions,
but nothing that obviously applies directly to the problem of blowing IRF510 devices at only
a few watts of power if the antenna is mis-matched.  Mention of using small resistance values
in series with gate drive is interesting, as is use of pi-net attenuators between exciter and
RF PA gate...to help control impedance?  While we look upon the MOSFET internal capacitance
as being a problem, it is interesting that some designs add a capacitor on the drain side of
things, apparently to limit the upper frequency capability and reduce 'spikes'.  The discussion
on single-ended versus push-pull is interesting from a technical view, but did not introduce
anything obvious that could help.

I suppose we have to first determine just what the exact cause of IRF510 failure might be,
then use that as the basis for designing a suitable solution.

Arv  K7HKL
_._




uBitx enclosure

at91r40008
 

The front panel is still plastic at this time. I painted in black to look more esthetic :)
The plug on the left is a mini XLR for the mike. On the right is a function switch.
In the back is another mini XLR for the USB connection for software update. I need
to find countersunk screws for the display.
I am going to install the Raduino X from WA6ISP Mike Haegen, it has way more
IOs available. I received it Monday but didn't have the time to
install it.


73, Yvon NU6I

Re: Second batch of uBITX shipping? #ubitx

Dgyuro
 

Ordered 17 Dec. still waiting.  

Sent from my iPhone

On Jan 25, 2018, at 9:43 PM, mikael.madsen@... wrote:

Someone posted that order date 14th december had been shipped but that was some days ago.

Anyone with a later order date later than 14th been informed of shiping yet?

Re: Something has been blown

chris gress <Chrisg0wfh@...>
 

I got these from a UK supplier I think from eBay or amazon can not remember they are good parts not fakes I have 3 bitx not blown a pa yet each one has a restive bridge swr unit fitted so protected when turning chris

On 26 Jan 2018 04:35, "Jerry Gaffke via Groups.Io" <jgaffke=yahoo.com@groups.io> wrote:
If the IRF510's still draw some current through PA-PWR during transmit,
and that current changes when you adjust the gate bias with RV2 and RV3
(adjust this very carefully, as it quickly goes to hundreds of mA)
then the IRF510's are probably just fine.

Regarding cheap IRF510's on ebay, you might read this old thread:
    https://groups.io/g/BITX20/topic/5554568
They cost $1 on mouser for singles, below $0.50 if you buy lots, and you know who made it.
I don't see much point in buying on ebay.

As Arv says, make sure you have a good 50 ohm dummy load when testing.
Perhaps get four Xicon 200 ohm 3W metal film resistors (mouser 283-200-RC)
when buying the spare IRF510's.

Jerry, KE7ER



On Thu, Jan 25, 2018 at 07:31 pm, Arv Evans wrote:
Since there is no short with the IRF-510 devices in place but not connected to the chassis, it is 
possible that the antenna was disconnected, shorted, or some other anomaly.  Unfortunately
MOSFETs used as RF power amplifiers tend to self-destruct if the load is not of proper
impedance.  Too low an impedance and they will overheat, and too high an impedance and
they will go into oscillation and destroy themselves with high current. 

As Bernie KC9SGV has suggested replacement devices are relatively inexpensive from Ebay
vendors.  Some will probably raise the issue of Ebay sourced parts being less than perfect
but I have been using Ebay sourced IRF-510's for over 10 years with no problems. 


Re: IRF510 amplifier failures

M Garza <mgarza896@...>
 

Here is another:

In the middle of the page, is this:

"I destroyed many IRF510 FETs during testing. In fact I blew a small hole in one and another into several pieces. It was quite a shock when the first one was destroyed because it made a loud noise like a rifle being fired.

Once I got tired of replacing the FETs, I built a current sense circuit, which shuts off the bias once the amplifier draws more than about 3 amps from the PSU. I think this circuit is essential. You can build it into the Power Supply or into the Amplifier. I built it into the Amplifier because the power supply, which is also homemade, does not limit until 7 amps. With the current limit circuit the amplifier now survives transmitting into any SWR from an open circuit to a short."

There is a schematic for the current limiting circuit that is used.  This might be something to incorporate into the design.  It is only 7 more parts.


Marco - KG5PRT


On Thu, Jan 25, 2018 at 10:48 PM, Arv Evans <arvid.evans@...> wrote:
Hello

The problem with IRF510 RF amplifiers failing seems to be a recurring one for those who
are not quite careful with antenna matching, bias level, and drive level.  As a way to start
looking into this situation I have performed some on-line searches to see how others are
And there is much more out there to be Google searched and reviewed.

There are a number of potentially useful ideas contained in those articles and discussions,
but nothing that obviously applies directly to the problem of blowing IRF510 devices at only
a few watts of power if the antenna is mis-matched.  Mention of using small resistance values
in series with gate drive is interesting, as is use of pi-net attenuators between exciter and
RF PA gate...to help control impedance?  While we look upon the MOSFET internal capacitance
as being a problem, it is interesting that some designs add a capacitor on the drain side of
things, apparently to limit the upper frequency capability and reduce 'spikes'.  The discussion
on single-ended versus push-pull is interesting from a technical view, but did not introduce
anything obvious that could help.

I suppose we have to first determine just what the exact cause of IRF510 failure might be,
then use that as the basis for designing a suitable solution.

Arv  K7HKL
_._





Re: Second batch of uBITX shipping? #ubitx

Ralph Richard
 

15th and no word

Virus-free. www.avast.com

Re: Something has been blown

 

You will surely have burnt power tracks. Trace the final power line.

Raj

At 26/01/2018, you wrote:
now, with finals away from the metal chasis I am testing if I have output. The power meter and needle doesnt move at all. I do get about 1,3amp drain when ptt and i can hear myself on other radio though.
I have tested with another watt metter with no joy either

maybe its too weak to be afected

Re: IRF510 amplifier failures

Arv Evans
 

Marco - KG5PRT

That is very interesting indeed.  Implementing this current based bias control
should be easy and could be compact. 


Inline image 1
from: http://www.g0kla.com/scpa/SimpleCheapPA.php

If I understand this correctly...
  • Voltage drop across R1 forward biases T2 to ON state
    This lights the LED.
  • Voltage on the collector of T2 turns T1 OFF, removing supply voltage
    to the 5V bias regulator in the RF PA circuit.

I was looking toward a similar control based on reflected power but the current
based approach is easier, as long as it works.  This adds another project to my
to-do list.

Thanks for the URL.

Arv  K7HKL
_._


On Thu, Jan 25, 2018 at 10:11 PM, M Garza <mgarza896@...> wrote:
Here is another:

In the middle of the page, is this:

"I destroyed many IRF510 FETs during testing. In fact I blew a small hole in one and another into several pieces. It was quite a shock when the first one was destroyed because it made a loud noise like a rifle being fired.

Once I got tired of replacing the FETs, I built a current sense circuit, which shuts off the bias once the amplifier draws more than about 3 amps from the PSU. I think this circuit is essential. You can build it into the Power Supply or into the Amplifier. I built it into the Amplifier because the power supply, which is also homemade, does not limit until 7 amps. With the current limit circuit the amplifier now survives transmitting into any SWR from an open circuit to a short."

There is a schematic for the current limiting circuit that is used.  This might be something to incorporate into the design.  It is only 7 more parts.


Marco - KG5PRT


On Thu, Jan 25, 2018 at 10:48 PM, Arv Evans <arvid.evans@...> wrote:
Hello

The problem with IRF510 RF amplifiers failing seems to be a recurring one for those who
are not quite careful with antenna matching, bias level, and drive level.  As a way to start
looking into this situation I have performed some on-line searches to see how others are
And there is much more out there to be Google searched and reviewed.

There are a number of potentially useful ideas contained in those articles and discussions,
but nothing that obviously applies directly to the problem of blowing IRF510 devices at only
a few watts of power if the antenna is mis-matched.  Mention of using small resistance values
in series with gate drive is interesting, as is use of pi-net attenuators between exciter and
RF PA gate...to help control impedance?  While we look upon the MOSFET internal capacitance
as being a problem, it is interesting that some designs add a capacitor on the drain side of
things, apparently to limit the upper frequency capability and reduce 'spikes'.  The discussion
on single-ended versus push-pull is interesting from a technical view, but did not introduce
anything obvious that could help.

I suppose we have to first determine just what the exact cause of IRF510 failure might be,
then use that as the basis for designing a suitable solution.

Arv  K7HKL
_._






Re: IRF510 amplifier failures

Jerry Gaffke
 

A suitable fast-blow fuse or polyswitch in the PA-PWR line into the board should be sufficient
to protect the IRF510's from too much current.
The polyswitch is like a fuse, except it resets once it cools down after you remove power.
A thermal sensor on the IRF510 heatsink that at least turns on a front panel LED might be a good idea.

This old post here from Allison is informative, well worth re-reading every few months:
    https://groups.io/g/BITX20/message/22597
As she says, lots of things can kill an IRF510, but the most common is heat if you have a good amp design.
Powering at 28v for 55W from a push-pull pair, she didn't see trouble when driving improper antenna impedances.

I'd think that if powered at 12v, and if they have a reasonable heatsink, and if you don't screw up 
when fiddling with the gate bias pots at rv2 and rv3, or drop a screwdriver into the wrong spot,
the IRF510's should not blow.  Even when driving a non-existent antenna, the RF voltages at the drains
go up some without a load, but not drastically, T11 is just a 1:2 voltage transformer.
Driving a 0 ohm antenna might be a bit worse since the currents will go up, but probably survivable.

Jerry, KE7ER


On Thu, Jan 25, 2018 at 09:11 pm, M Garza wrote:

There is a schematic for the current limiting circuit that is used.  This might be something to incorporate into the design.  It is only 7 more parts.

 

Re: IRF510 amplifier failures

M Garza <mgarza896@...>
 

Jerry,
I do not disagree, I have a fuse inline with both power lines.  When a fuse blows, you dont know if there has been damage or not.
In my opinion, it would be better to prevent the situation from being able to happen.  This idea seems to have worked for the builder, 
since he made specific mention of it. 
"With the current limit circuit the amplifier now survives transmitting into any SWR from an open circuit to a short."

Marco - KG5PRT


On Thu, Jan 25, 2018 at 11:37 PM, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:
A suitable fast-blow fuse or polyswitch in the PA-PWR line into the board should be sufficient
to protect the IRF510's from too much current.
The polyswitch is like a fuse, except it resets once it cools down after you remove power.
A thermal sensor on the IRF510 heatsink that at least turns on a front panel LED might be a good idea.

This old post here from Allison is informative, well worth re-reading every few months:
    https://groups.io/g/BITX20/message/22597
As she says, lots of things can kill an IRF510, but the most common is heat if you have a good amp design.
Powering at 28v for 55W from a push-pull pair, she didn't see trouble when driving improper antenna impedances.

I'd think that if powered at 12v, and if they have a reasonable heatsink, and if you don't screw up 
when fiddling with the gate bias pots at rv2 and rv3, or drop a screwdriver into the wrong spot,
the IRF510's should not blow.  Even when driving a non-existent antenna, the RF voltages at the drains
go up some without a load, but not drastically, T11 is just a 1:2 voltage transformer.
Driving a 0 ohm antenna might be a bit worse since the currents will go up, but probably survivable.

Jerry, KE7ER


On Thu, Jan 25, 2018 at 09:11 pm, M Garza wrote:

There is a schematic for the current limiting circuit that is used.  This might be something to incorporate into the design.  It is only 7 more parts.