OP, I don't think you're wrong. I also don't think your husband is necessarily wrong in what he wants. Different people find happiness in different things.
Perhaps a compromise can be had, like the previous suggestion of selling your existing TVs to buy a larger used TV. Definitely I would not suggest buying it on credit, regardless of interest rate. Debt is debt, and debt habits are hard to shake.
I think the idea behind putting money in a jar is just making sure you & he have the cash in hand to buy the TV outright, and if you don't, you wait until you do. I don't know enough about you, your husband, your finances, or your mutual frugality to know whether the TV thing is a one-off or a habit for your husband.
You could look at this as an opportunity: You give in on this, but he owes you one big favor to be named later. It could be a big expense, or it could be you getting to say no to a big expense he wants, no questions asked. It could be him doing all the dishes, laundry, child care, and/or vacuuming for a year. Whatever works for you. He gets something, you get something. Give and take. This has the added bonus of increasing the overall price he pays for a flashy thing, which might make him consider carefully next time. :)
My spouse is spendier than I am, but that doesn't bother me; we're just different people. But we agree on the big financial philosophies, and we are moving steadily toward our goals. To me, that's more important than an individual expensive purchase.