Issue with low pass filter board. Inductors getting hot.

[Darryl]

Hello everyone.  I'm looking for some advice from the group.

In testing out my new construction, I've run into a temperature problem with the low pass filter.

I put the amp in service in kind of a kludged fashion while testing it.  Amp module, T/R switch and LPF all in hooked up properly to the best of my knowledge.  Amp output connected to LPF input and LPF output connected to the T/R Amp output connector.  This was a live test into an MFJ-998 antenna tuner (and doublet antenna) and I made sure the SWR was 1:1 before the test. I was running about 60W according to the MFJ tuner's Watt meter. For this test I used 80M (~3.7 MHz) and jumpered the band connector on the LPF board so that pin 1 was grounded, activating relays Y11 and Y12.

When in transmit, the 80M filter inductors (L6A and L6B) get very, very hot. L6A gets especially hot, and L6B to a lesser degree. While I was testing I smelled something overheating and it was L6A.  I took a FLIR photo of the board so you can see what I am talking about. You can see the heat from the energized relays and also the heat from the inductors.

Here is a photo of the board:

After initially putting the LPF board together,  I powered it up and swept it with my spectrum analyzer.  Everything looked good.  As I changed bands I could see the frequency cutoff change as expected. Nothing looked out of the ordinary.

Any ideas as to what the issue could be would be appreciated. The excess heat in the inductors has caught me by surprise.

Regards,

Darryl

N0DP

[jcve...@gmail.com]

The T50 cores get hot. It's not out of spec for the toroid cores (+200C) or for the wire (+180C).

Probably best not to touch them!

73,

Jim WA2EUJ

[Darryl - N0DP]

Thanks Jim.

L6A got so hot it burned the paint off the top of the toroid and fractured the ferrite.  I had to re-wind another and put it on the board.  I think I'll keep the power down a bit!

I thought maybe I had purchased a bad batch of T50-2 material or some such or had another issue.

Regards,

Darryl

[Darryl - N0DP]

I've re-ordered some T50-2 cores to rule out bad material.  I'll re-wind the two 80M cores and re-test.

If those that have an amplifier working can share their experience of the LPF toroid temperatures during transmit, I would appreciate it.

Regards,

Darryl

N0DP