This can be confusing. In literature, sometimes a narration may take place in the past, as in English, but certain points may be in the present tense. 麻衣子は目が覚めた。いい天気の日だ。Maiko woke up. It is (was) a clear day.
Other times, even in speech, you need to take into account the progression of time and how actions relate to each other:
A) 日本に行くとき、英和辞書を買います。When I go to Japan (but before I get there) I will buy an English-Japanese dictionary.
B) 日本に行ったとき、英和辞書を買います。When I go to (and arrive in) Japan I will buy an EJ dictionary.
C) 日本に行くとき、英和辞書を買いました。When I went to Japan (but before I actually left) I bought an EJ dictionary.
D)日本に行ったとき、英和辞書を買いました。When I went to (and arrived in) Japan I bought an EJ dictionary.
The final verb dictates the overall tense of the sentence, but the first verb, 行く, states whether or not the first action has taken place/was completed or not before buying the dictionary.
All are acceptable, depending on context, but perhaps 1 and 3 would be most common.
1) テレビが私の国で 《できた》 のは１９６０ 《です》。1960 is when the television was made in my country. (Listing the year it was invented)
2) テレビが私の国で 《できる》 のは１９６０ 《です》。 1960 is when the television will be made in my country. (Listing off accomplishments as part of a retrospective or narration?)
3) テレビが私の国で 《できた》 のは１９６０ 《でした》。1960 was when the television was made in my country. (giving a fact)
4) テレビが私の国で 《できる》 のは１９６０ 《でした》。1960 was when the television will be made. (Sounds like people are time travelling)
