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50 Watt amp with external LPF

 

In an attempt to reduce the number of amplifiers needed for my QCX and QDX I decided to try and make some external LPF filters that could be easily changed out depending on the band of choice. I purchase a 50 W amp kit and jumped out L4, L6, and L7 and did not install any of the capacitors associated with the LPF. I had an LPF kit available and used only the PC board replacing the toriods with the T50-6 from the 50W amp as well as the higher voltage capacitors from the 50 W kit. I built the first LPF for 20 meters and my NanoVNA showed the 3db down point at about 14.200 MHz and has a max attenuation of -37db at about 24 MHz. Tests showed a power output of ~20 watts with 13.0 VDC input to the QCX and 50-watt amp. Dropping the voltage to 12 VDC reduced the power to about 17 watts. I am currently starting to build a 40-meter LPF and need to get some parts so I also build some additional LPFs for other bands.

The photos show the LPF and LPF attached to the amp. The overall length of the LPF is 90mm (3.55 Inches). The box itself is 54mm long and 23mm square. I will be installing a cover on the LPF. The box was constructed of double-side PC board but the next one will be made of single-side PC board perhaps with the exception of the ends.

If someone else has successfully built some external LPFs for the 50-watt amp I would like to see what you have done so I might improve my design. I currently awaiting the 1.04 firmware for the QDX so I can try it out on that transceiver.

Dennis
KK5DB
 

Dennis, I did the same thing but used die cast aluminum boxes for the housing. I should have used the male chassis connector on one end like you did though. In my case, the 50 watt amp was built with the 20 meter filter installed internally, and the 30 and 40 meter filters are only added on externally?when needed for those bands. The loss in the always-in-circuit 20 meter filter is very low, so normal expected outputs?can be achieved on all three bands.... Your internals look very nice. I just used copper clad?board and constructed the filters "dead bug style". ?73 ...?

Ron
WA7GIL




On Fri, Jun 17, 2022 at 4:13 PM Dennis Rieger <kk5db@...> wrote:
In an attempt to reduce the number of amplifiers needed for my QCX and QDX I decided to try and make some external LPF filters that could be easily changed out depending on the band of choice. I purchase a 50 W amp kit and jumped out L4, L6, and L7 and did not install any of the capacitors associated with the LPF. I had an LPF kit available and used only the PC board replacing the toriods with the T50-6 from the 50W amp as well as the higher voltage capacitors from the 50 W kit. I built the first LPF for 20 meters and my NanoVNA showed the 3db down point at about 14.200 MHz and has a max attenuation of -37db at about 24 MHz. Tests showed a power output of ~20 watts with 13.0 VDC input to the QCX and 50-watt amp. Dropping the voltage to 12 VDC reduced the power to about 17 watts. I am currently starting to build a 40-meter LPF and need to get some parts so I also build some additional LPFs for other bands.

The photos show the LPF and LPF attached to the amp. The overall length of the LPF is 90mm (3.55 Inches). The box itself is 54mm long and 23mm square. I will be installing a cover on the LPF. The box was constructed of double-side PC board but the next one will be made of single-side PC board perhaps with the exception of the ends.

If someone else has successfully built some external LPFs for the 50-watt amp I would like to see what you have done so I might improve my design. I currently awaiting the 1.04 firmware for the QDX so I can try it out on that transceiver.

Dennis
KK5DB

 

Nice work gents¡­

Ron, where did you source the die-cast aluminum enclosures? It would be great to include an OEM part number too.?

Paul, W9AC
 

I favor the 1590A style enclosure from Tayda Electronics for this kind of small project. ?This box is 92x38x30mm, and is $4 in cast aluminum finish. ?And for 30 cents more, you can get one in color! ?Diecast aluminum boxes of this size have been available from various manufacturers for decades. ?Here is a filter I built in a Bud box more than 40 years ago.

73, Ben ?K0IKR
 

Paul, Ben's suggestion is a good one. I sourced mine from Amazon. Just put "1590A" in their search engine and you'll see options for multiple quantities .... still in the $5 each price range.?

Ron

On Sat, Jun 18, 2022 at 6:41 AM Ben Bangerter, K0IKR via <bwbangerter=[email protected]> wrote:

I favor the 1590A style enclosure from Tayda Electronics for this kind of small project.? This box is 92x38x30mm, and is $4 in cast aluminum finish.? And for 30 cents more, you can get one in color!? Diecast aluminum boxes of this size have been available from various manufacturers for decades.? Here is a filter I built in a Bud box more than 40 years ago.

73, Ben ?K0IKR
 

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Nice! ?I especially like the colored ones, but now we need a standard for BPF frequency and housing color. ?8*)

73, Willie N1JBJ

On Jun 18, 2022, at 10:26 AM, Ronald Taylor <wa7gil@...> wrote:

?Amazon. Just put "1590A" in their search engine
 

Hi all

I tried to use the 50w amp with an external switching LPF

The idea is great

but when you align the amp on one band, it's for that band only

the best bet is to use the amp with lower voltage (i.e, 12 V and lower bias setting)

this filter worked the best


muhsin TA1MHS

73
 

Mushin, thanks for posting this info, exactly what?I was looking for.
73
Brad
W9BLH?

On Sat, Jun 18, 2022, 11:03 AM Muhsin Dogrular <muhsin.dogrular@...> wrote:

Hi all

I tried to use the 50w amp with an external switching LPF

The idea is great

but when you align the amp on one band, it's for that band only

the best bet is to use the amp with lower voltage (i.e, 12 V and lower bias setting)

this filter worked the best


muhsin TA1MHS

73

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