Good info, old tubes OK?
Thanks Norman, good info. I'd add kboyd59, if you're buying used, you can get good deals on tube transponder. Tubes can last decades. Tubes die from both use and age, but they can be long lived. If buying a used unit, if you can get a quick bench test and determine if its on freq, sensitive to interrogation and power output is acceptable. You can't do that on eBay, but I have had good luck w/ transponders I bought.