[Boatanchors] Mixer Troubleshooting Question For my Homebrew Superhet Novice Receiver

[wa9wfa]

Many thanks Bill for the new video of your MMMRX in action!  What a sweet little receiver.  It is good for me to hear what a functional MMMRX should sound like for comparison.  I have a little ways to go yet with mine but it’s good to hear when it should end up sounding like once the issues are resolved.  Yes you do have adequate audio, even enough to drive a small speaker with.  My audio output is just enough to lightly drive the headphones right now so I have some work to do yet..  After I sent the email this morning I spent some time around the BFO, crystal filter, and IF amplifier.   

While the BFO is ‘working’ and I’m seeing a nice several volt strong sign wave that changes frequency when the BFO inductor is tuned, I don’t hear any change in the audio.  So it’s either no where near the IF frequency or there is insufficient coupling.   I am using a 6EA8 for V3 by the way.

As you found with your MMMRX, I also saw a tremendous attenuation through the crystal filter.  I don’t know how much attenuation I should expect but it was huge.  You mentioned using a Millen IF transformer in place of the dual crystal(s) filter.  I might try that for the time being just to keep things rolling while I figure out the crystal filter.  I have some 455 KC IF’s in the box.  This past summer I accidentally sold my last Collins 2.1 KHz filter after thinking I had 2 left, so that option is off the table at the moment.  So maybe the transformer will do in pinch for me just until I figure out issue.

Speaking of IF transformer, as I was peaking the 455 KC IF transformer just after the IF amplifier  I noted a widely changing voltage as the tool pressed on the sides of the transformer so I’ll need to look at that phenomenon.  It should be rock stable but it’s all over the place.  The connections look solid so maybe it’s something in the transformer.  Aw crap I might have to pull that transformer and replace it with another.  That area of construction is the 2nd tightest parts area in the chassis.  

I feel great that it’s at least working to a degree and I’m hearing some signals but nothing like yours yet.  I like how you put it, I’ll just have to work my way through it and coax the signals out of it.  Hi hi

Thanks for  your new video and advice.  73, Scott WA9WFA

> On Feb 28, 2021, at 11:53 AM, Bill Meara <n2cqr at yahoo.com> wrote:
> 
> Scott:   Here is the video of my MMMRX in action!  
> 
> https://youtu.be/1C2f1grNjOs <https://youtu.be/1C2f1grNjOs>
> 
> I would  work on the alignment, and think about how much loss those old crystals in the filter might be causing.  
> 
> Please let me know how this works out.  It was fun to fire mine up today.   
> 
> 73  Bill N2CQR
> http://soldersmoke.blogspot.com <http://soldersmoke.blogspot.com/>
>