A, AF, AX, D, DF, DX Version of HOT
If you repair CRT Monitor I’m sure you might have came across Philips Horizontal output transistor (HOT) that have many version behind each part number. For example, BU2508A, BU2520AF, BU 4522AX, BU4523DX and etc. For your information the A version does not have a built in damper diode but the D version have damper diode in it. You may refer to semiconductor databook or from the internet to see the specification of each HOT.
The question is, could an A version be replaced by the D version and vice versa? I understood that many repair technicians replaced the A version with the D version and did not replace the D version with the A version. The reason was that the HOT with a built in damper diode is much better than the HOT without damper diode in it. Yes, it is true that many of the Monitor in the market with the A version can be replaced with the D version but i did came across certain brand of Monitor that only can run well with the original part number! That means, the D version would not last. It worked for only a week or two before the HOT blow again. Putting back the A version solved the problem.
Since HOT is easily available from the market, i suggest that you put back the exact part number to avoid call back because a repeated repair is a loss to you and your business.