Atlas 110 transmitter rf fading after 2 min of CW

Both the transmitter and receiver work great, but after 2 minutes of CW, the rf output drops to nearly zero. Simply stopping CW for a few seconds, it returns to normal operation.

I have heard that there is a modification to a protection circuit that fixes this. There is no mention of such a circuit in the owners manual and if there is one, it is not obvious to me on the schematics.

Can you help ?

Many Thanx.

kd2pk.....greg 73
gwburrows@aol.com
607-207-1992

 

Fading power is usually the sign of something (semi conductor) getting too warm.
I'd check to make sure everything is properly heat sinked (Mounting & sufficient compound applied)
condition of any nylon mounting screws etc

PS
http://atlas.wireless.org.uk/mods.htm

 

Atlas 110 Line, the Twins. There were two versions (L and H) of the TX 110 --
based on power output.
http://wireless.org.uk/atlas/Atlas 110 Line Brochure.pdf


Photo from WB6VHK Collection

For your question / issue: Check your DC Power Supply and input. Loss of regulation, in linear DC supplies, can exhibit this type of problem.

Atlas TX-110 Schematic
http://atlas.wireless.org.uk/Atlas TX-110 Diagram.pdf

All About Atlas Radios
http://atlas.wireless.org.uk/

Service Bulletins
http://atlas.wireless.org.uk/mods.htm

eHam.net Reviews
http://atlas.wireless.org.uk/

 

to W9GB

AWW- COME ON ! The one to solve my problem has my initials ! (GB) mine are GWB..Talk about karma.

A THOUSAND THANK YOU'S !!!!

First, I apologize for the late reply. I have not looked at this forum since my post (assumed replies would go to my email.....DUH )

Anyway, at first, I did consider my power supply, but the voltages were what I thought were "close enought" and even though the lo voltage supply changed only 0.75 volts during the rf drop, I mistakenly dismissed it as normal.

So today, after seeing your post, I connected my rig to my bench supply instead of using the on-board supply. Result....... I could not get a change in rf, even after 3 minutes of "key-down".

So now I have to find and adapt a regulator chip since the one from Atlas is out of production. Not really a problem though.

Thankx again.

greg
73's
KD2PK

 

OK, I am a bit confused. WHAT are you using for the AC to 13.8 VDC power supply (that is failing)
for this Atlas Radio??

Is it the Atlas PS-110 matching power supply??

What is the regulator chip (IC) and Pass Transistor that you are looking for?
It should not be that difficult to repair !!

 

THe power supply I am using one is a small, variable one that I built in an NRI training course (CONAR) on electronics. It had also gone bad, the reg. chip died years ago and is also no longer available, so I replaced it with a new one by adapting it as well. I connected it to the 14V low power input on the back of the RX110 which bypasses the on board supply when was not plugged in..

The regulator chip is a 78MGT.... rather strange looking package. I think that I might just build a whole new supply with 9V and 14V outputs (1A each) using only the on board transformer.