Improved RX Sensitivity, Robyn 240D

[Tweek]

I originally did this mod sometime back, after a total restoration of a 240D for a friend. I had recapped the rig, and changed all of the out-of-tolerance resistors. A new set of tubes still wouldn't bring the RX up to what I had hoped for, it was hanging around .4uV @ 10dB. Not bad, and I think probably in spec for that rig, but I felt that tube lineup in the receiver should have been much better. Since then, he's collected several of these radios, and after modifying all of them the same way and having practically the same results, I don't mind sharing this info. They all seemed to start out around .4-.5uV in sensitivity.

I optimized the voltages on the 1st & 2nd mixers, and 1st I.F. amp. Here's the poop...

- Change R106 from 47K to 220K

- Change R201 from 680 ohms to 1200 ohms

- Install a 56k resistor in parallel with R303

All of his rigs improved between .07-.1uV @ 10dB, one actually hit about .05uV.

This should probably work on the other radios that are basically the same Panasonic chassis...T-Berry, Colt, Gemtronix. Maybe the 23 channel stuff like the Comstats, but compare the mixer and I.F. stages to those schematics before you venture off to change stuff

 

[grimace]

https://wb4iuy.blogspot.com/2019/02/robyn-240d.html

 

[Tweek]

https://wb4iuy.blogspot.com/2019/02/robyn-240d.html

Yep, that would be me

 

[grimace]

ok good job lot of info on your site

 

[Shadetree Mechanic]

I love my yellow Robyn. I just don't have much room on the desk. I am going to put it on the bench to see if I can identify the spots you showed. Then I will get the parts together to make the changes. Thanks for sharing!

 

[Tweek]

ok good job lot of info on your site

Thanks, I've been typing on there for many years. I use it to keep track of a bunch of things I may forget otherwise

 

[Shadetree Mechanic]

Here is my thread about how I made some room in my shack for the Robyn with a new little shelf.

https://www.worldwidedx.com/threads/my-little-shack-new-shelf.238004/

 

[Tweek]

Nice work on the shack!!