Before you go too far I suggest that you ask your local friendly radtec to check the impedence of your earphones.
Get him to explain the difference between some military headsets / radios and civvie combinations. USA works on a different impedence from OZ for example. Most OZ army machines seem to work on USA military standards.
I have seen so many OZ ex military jocks get into a civvie model, and plug in, and then the civvie is totally drowned out. makes me bloody mad it does.
Not only that, a wrong impedence or an nearly worn out microphone also often snuffs out the radio. This may be where your radio is now with your serious comprehension problems.
make sure you ask your boss ( flight instructor) to check it out because he is the one who continuously pays for the repair and he may not be aware of the imcompatibility problems.
Where did you buy your headset??
In the meantime, ban ex military types with their special (free) olive green bone domes from going anywhere near your prescious radios.
As far as old radios are concerned, if you want to get blown out of the ether, be careful when you get close to a well performing valve set.