Topics

50W PA Damaged

Curt M.
 

Hi guys, I did one of those things this evening that I never thought I’d do. I held down the key to my QCX connected to the 50w amp and noticed that it didn’t want to tune. I saw my power meter drop and realized that I had my antenna switch set for the wrong port. I’m using a bench power supply with the current limit set for 7amps. 


So it’s obvious that something happened to the amp but I’m too tired to get involved with it at 2am. Is there any chance that it’s just the final?  Not sure if I should order a couple of replacements which I know I don’t have on hand or just order a new kit. I’m sure someone else out there has done this same thing and I’m wondering what it took to bring it back to life?  

Curt M.

J P Watters
 

I think this will be me at some point. 

My thought is to install a ATU like this one to protect the finals from transmitting into an open antenna.SDR rig to protect the finals. 
https://github.com/Dfinitski/N7DDC-ATU-100-mini-and-extended-boards
Will that ATU provide that kind of protection.

..jpw J P Watters
KC9KKO





George Korper
 

Usually, it is just the finals. That has been my experience in the same exact circumstance. 


On Sat, May 30, 2020 at 2:22 AM J P Watters via groups.io <kc9kko=mac.com@groups.io> wrote:
I think this will be me at some point. 

My thought is to install a ATU like this one to protect the finals from transmitting into an open antenna.SDR rig to protect the finals. 
https://github.com/Dfinitski/N7DDC-ATU-100-mini-and-extended-boards
Will that ATU provide that kind of protection.

..jpw J P Watters
KC9KKO





geoff M0ORE
 

I don't think any ATU will prevent damage to a transmitter due to human error. The commercial and military  equipment employ extensive circuitry in the transmitter to take care of such mishaps and shut down to a safe level. A soldier under fire can be forgiven for not checking the aerial matching. Likewise, an aerial on a vehicle may be damaged without the operator being aware of the damage.

An ATU is basically a means of transforming one impedance to another. If no load is connected i.e. a very high impedance, then that is reflected back through the ATU to your transmitter as a very high impedance. Hence the blown finals.

You could design an interlock system such that if the aerial is not connected the transmitter does not power up.



On 30/05/2020 11:28, George Korper wrote:
Usually, it is just the finals. That has been my experience in the same exact circumstance. 

On Sat, May 30, 2020 at 2:22 AM J P Watters via groups.io <kc9kko=mac.com@groups.io> wrote:
I think this will be me at some point. 

My thought is to install a ATU like this one to protect the finals from transmitting into an open antenna.SDR rig to protect the finals. 
https://github.com/Dfinitski/N7DDC-ATU-100-mini-and-extended-boards
Will that ATU provide that kind of protection.

..jpw J P Watters
KC9KKO





Bill Cromwell
 

Hi,

It isn't possible to pass laws nor make any equipment of any kind "idiot proof". As soon as we design or legislate to protect from idiots then better idiots will be made :)

73,

Bill KU8H

On 5/30/20 7:12 AM, geoff M0ORE via groups.io wrote:
I don't think any ATU will prevent damage to a transmitter due to human error. The commercial and military  equipment employ extensive circuitry in the transmitter to take care of such mishaps and shut down to a safe level. A soldier under fire can be forgiven for not checking the aerial matching. Likewise, an aerial on a vehicle may be damaged without the operator being aware of the damage.
An ATU is basically a means of transforming one impedance to another. If no load is connected i.e. a very high impedance, then that is reflected back through the ATU to your transmitter as a very high impedance. Hence the blown finals.
You could design an interlock system such that if the aerial is not connected the transmitter does not power up.
--
bark less - wag more

George Korper
 

Using Allison's suggestion, a 4 amp fuse sometimes will blow before the finals in the
event of no antenna connected. Also using Allsion's tapping technique is easy and makes
replacing the two IRF510's a breeze. 
Having this occur doesn't mean you're an idiot. 
Sometimes I have left the house without a mask, and then I feel like an idiot. 
Now I leave one in the car!
It happens to all of us one time or another. I have made use of three sets of spares (hi hi)
Just make sure you order 10 at a time (five sets) as they are not expensive and use a Vishay or equivalent high quality
part from a supplier like Digikey or Mouser. 

On Sat, May 30, 2020 at 7:46 AM Bill Cromwell <wrcromwell@...> wrote:
Hi,

It isn't possible to pass laws nor make any equipment of any kind "idiot
proof". As soon as we design or legislate to protect from idiots then
better idiots will be made :)

73,

Bill  KU8H

On 5/30/20 7:12 AM, geoff M0ORE via groups.io wrote:
> I don't think any ATU will prevent damage to a transmitter due to human
> error. The commercial and military  equipment employ extensive circuitry
> in the transmitter to take care of such mishaps and shut down to a safe
> level. A soldier under fire can be forgiven for not checking the aerial
> matching. Likewise, an aerial on a vehicle may be damaged without the
> operator being aware of the damage.
>
> An ATU is basically a means of transforming one impedance to another. If
> no load is connected i.e. a very high impedance, then that is reflected
> back through the ATU to your transmitter as a very high impedance. Hence
> the blown finals.
>
> You could design an interlock system such that if the aerial is not
> connected the transmitter does not power up.

--
bark less - wag more



George Korper
 

Of course if I choose not to wear a mask in the middle of an epidemic
then I would probably be an idiot. 

On Sat, May 30, 2020 at 8:08 AM George Korper <georgekorper@...> wrote:
Using Allison's suggestion, a 4 amp fuse sometimes will blow before the finals in the
event of no antenna connected. Also using Allsion's tapping technique is easy and makes
replacing the two IRF510's a breeze. 
Having this occur doesn't mean you're an idiot. 
Sometimes I have left the house without a mask, and then I feel like an idiot. 
Now I leave one in the car!
It happens to all of us one time or another. I have made use of three sets of spares (hi hi)
Just make sure you order 10 at a time (five sets) as they are not expensive and use a Vishay or equivalent high quality
part from a supplier like Digikey or Mouser. 

On Sat, May 30, 2020 at 7:46 AM Bill Cromwell <wrcromwell@...> wrote:
Hi,

It isn't possible to pass laws nor make any equipment of any kind "idiot
proof". As soon as we design or legislate to protect from idiots then
better idiots will be made :)

73,

Bill  KU8H

On 5/30/20 7:12 AM, geoff M0ORE via groups.io wrote:
> I don't think any ATU will prevent damage to a transmitter due to human
> error. The commercial and military  equipment employ extensive circuitry
> in the transmitter to take care of such mishaps and shut down to a safe
> level. A soldier under fire can be forgiven for not checking the aerial
> matching. Likewise, an aerial on a vehicle may be damaged without the
> operator being aware of the damage.
>
> An ATU is basically a means of transforming one impedance to another. If
> no load is connected i.e. a very high impedance, then that is reflected
> back through the ATU to your transmitter as a very high impedance. Hence
> the blown finals.
>
> You could design an interlock system such that if the aerial is not
> connected the transmitter does not power up.

--
bark less - wag more



 

At risk of getting wildly O/T, and getting soundly scolded for it... There are plenty of those around, unfortunately.
I am astounded by the number of people who rationalize away their own health and put their own lives and the lives of others at risk for the temporary hedonistic reward gifted by blissful ignorance and denial.
Well over 100,000 deaths now, in this country alone. At what point do we (collectively, as a society) learn to think of each other and act accordingly?

OK, done now.

Julian N4JO.

R. Tyson
 

Hi,

It can certainly help if you incorporate a balanced bridge circuit into the ATU. That way you can tune up and the PA sees a 50 ohm load even when the antenna is not yet balanced.

The slight inconvenience is that you have to switch from "tune" to "straight though" forgetting to do so results in a much lower transmitted signal than you intended.... don't ask...

Reg                     G4NFR

George Korper
 

REALIZING being an intentional idiot and just forgetting to do something is an important distinction,
I posted around the shack letter size warnings to myself. Like: "IS YOUR ANTENNA CONNECTED?"
This has been very helpful. I never did this growing up...before age 70, and over the years, I was saved by rigs
with internal safeguards. The QCX has taught me a lesson in self reliance. Here's another:
"DO NOT RUN IN PRACTICE MODE WITHOUT A DUMMY LOAD."  Yup, even practice mode can be
be thwarted by the inner devious Coyote. It comes out when i'm sleepy. 

On Sat, May 30, 2020 at 10:52 AM R. Tyson via groups.io <tysons2=btinternet.com@groups.io> wrote:
Hi,

It can certainly help if you incorporate a balanced bridge circuit into the ATU. That way you can tune up and the PA sees a 50 ohm load even when the antenna is not yet balanced.

The slight inconvenience is that you have to switch from "tune" to "straight though" forgetting to do so results in a much lower transmitted signal than you intended.... don't ask...

Reg                     G4NFR

Curt M.
 

Just ordered a small handful of them and got the bad ones pulled out. Hopefully that’s all it is. Will post after I replace them later this upcoming week. 


Curt M

ajparent1/KB1GMX
 

It is a high power amp,  and like many its subject to doing things one should
consider natural if it happens.  For example fail if not hooked to an antenna
or other reasonable load.

Its also a training device it rewards error with the pain of replacing about
1.60$ transistor.  Be glad its not a device that's easily 50-100 times more
expensive or scarce.  I got a nice 2M 600W amp module free when its
former owner oopsed the BLF184XR., new transistor is 160$.

Replace both of the devices, dial in the bias be carefully per manual
and if possible lower power for tune up.  Dropping from 20V to 13v will
likely preserve the IRF510s in adverse cases and the antenna will tune
just the same.

Or better yet use a MFJ259 or a NanoVNA to tune up the antenna
then connect it to the radio.

Allison
-------------------------------
Please reply on list so we can share.
No private email, it goes to a bit bucket due address harvesting

Paul AI4EE
 

"Generally, the designers of idiot-proof systems do not take into account the ingenuity of idiots." -- Author Unknown

On 5/30/2020 7:46 AM, Bill Cromwell wrote:
Hi,

It isn't possible to pass laws nor make any equipment of any kind "idiot proof". As soon as we design or legislate to protect from idiots then better idiots will be made :)

73,

Bill  KU8H

On 5/30/20 7:12 AM, geoff M0ORE via groups.io wrote:
I don't think any ATU will prevent damage to a transmitter due to human error. The commercial and military  equipment employ extensive circuitry in the transmitter to take care of such mishaps and shut down to a safe level. A soldier under fire can be forgiven for not checking the aerial matching. Likewise, an aerial on a vehicle may be damaged without the operator being aware of the damage.

An ATU is basically a means of transforming one impedance to another. If no load is connected i.e. a very high impedance, then that is reflected back through the ATU to your transmitter as a very high impedance. Hence the blown finals.

You could design an interlock system such that if the aerial is not connected the transmitter does not power up.

Paul AI4EE
 

"A transistor protected by a fast-acting fuse will protect the fuse by blowing first." -- corollary to Murphy's Law


On 5/30/2020 8:08 AM, George Korper wrote:
Using Allison's suggestion, a 4 amp fuse sometimes will blow before the finals in the
event of no antenna connected. Also using Allsion's tapping technique is easy and makes
replacing the two IRF510's a breeze. 
Having this occur doesn't mean you're an idiot. 
Sometimes I have left the house without a mask, and then I feel like an idiot. 
Now I leave one in the car!
It happens to all of us one time or another. I have made use of three sets of spares (hi hi)
Just make sure you order 10 at a time (five sets) as they are not expensive and use a Vishay or equivalent high quality
part from a supplier like Digikey or Mouser. 

On Sat, May 30, 2020 at 7:46 AM Bill Cromwell <wrcromwell@...> wrote:
Hi,

It isn't possible to pass laws nor make any equipment of any kind "idiot
proof". As soon as we design or legislate to protect from idiots then
better idiots will be made :)

73,

Bill  KU8H

On 5/30/20 7:12 AM, geoff M0ORE via groups.io wrote:
> I don't think any ATU will prevent damage to a transmitter due to human
> error. The commercial and military  equipment employ extensive circuitry
> in the transmitter to take care of such mishaps and shut down to a safe
> level. A soldier under fire can be forgiven for not checking the aerial
> matching. Likewise, an aerial on a vehicle may be damaged without the
> operator being aware of the damage.
>
> An ATU is basically a means of transforming one impedance to another. If
> no load is connected i.e. a very high impedance, then that is reflected
> back through the ATU to your transmitter as a very high impedance. Hence
> the blown finals.
>
> You could design an interlock system such that if the aerial is not
> connected the transmitter does not power up.

--
bark less - wag more



Paul AI4EE
 

If no one got vaccinated against the yearly influenza strains, very likely there would be close to 100,000 deaths a year from that. We're only as safe as we try to be. As they used to say on that cop show, "Let's be careful out there."


On 5/30/2020 10:05 AM, Julian Opificius wrote:
At risk of getting wildly O/T, and getting soundly scolded for it... There are plenty of those around, unfortunately.
I am astounded by the number of people who rationalize away their own health and put their own lives and the lives of others at risk for the temporary hedonistic reward gifted by blissful ignorance and denial.
Well over 100,000 deaths now, in this country alone. At what point do we (collectively, as a society) learn to think of each other and act accordingly?

OK, done now.

Julian N4JO.

Bill Cromwell
 

Hi,

I served in The Navy and *nothing* is sailor proof!

73,

Bill KU8H

On 5/30/20 3:30 PM, Paul AI4EE wrote:
"Generally, the designers of idiot-proof systems do not take into account the ingenuity of idiots." -- Author Unknown
On 5/30/2020 7:46 AM, Bill Cromwell wrote:
Hi,

It isn't possible to pass laws nor make any equipment of any kind "idiot proof". As soon as we design or legislate to protect from idiots then better idiots will be made :)

73,

Bill  KU8H
--
bark less - wag more

Curt M.
 

I received my IRF510s from Digikey. Got them installed and recalibrated the bias current. I’m back up and running. Puts out 60w into a dummy load so I’ll have to drop the supply down a little to keep things in check.

For those of you that are just building one of these or need to replace the finals I highly suggest using Kapton tape to hold the pads in place rather than electrical tape. It’s much thinner and the IRF510s clear them much easier than black tape. 


Curt M.