life expectancy of various amplifier tubes

[k4zmi]

I've looked around a bit but can't find expected life spans of these tubes;

3-500zg
3cx1200a7
3cx1500/8877

My concearn is the 3-500zg is so much cheaper than the 8877. Due to costs, does the 8877 last three or more times longer than the 3-500zg? Which tube is better with the life expectancy/cost factor?

[K4ICL]

I will try to provide you a semi-valid answer.

The expected service life of any component is directly related how it is used. Like a person, if it is abused it will not last as long.

In the case of tubes, if you operate any of the tubes you list WITHING THE DESIGNED SPECIFIED RATINGS of the tube they could be no difference between the types of tube. Please note that all three types you mention are designed for long term use on critical communications equipment.

So will a 3-500ZG last as long as a 3CX1200A7? Probably, but the latter will produce greater power output since it is designed to handle about 1,200 watts plate dissipation whereas one 3-500Z is rated at about 500 watts.

Perhaps the question should be, " will three 3-500ZG tubes, connected in parallel, last as long as a 3CX1200A7?" The answer, probably longer. Why? Three are used providing 1,500 plate dissipation, slightly greater than the 1,200 rated 3CA1200A7. ...But NOT three times longer, it doesn't work that way.

But there are complications. For example, the grids of the 3-500 design tube will take greater grid drive than the 3CX1200A7, which is very picky about not having too much grid drive. So if you "push" a 3CX1200A7, you can be assured it will not last as long.

Confused?

Go back to the beginning. How long the different tubes will last is totally dependent on HOW they are used.

Cheers,

K4ICL

[k4zmi]

Well sir, that's some useful info, but not quite what I meant.

Since the 8877 and the 3cx1200a7 costs so much more than the 3-500, maybe 3 to 4 times as much, would the two higher priced tubes last 3 to 4 times longer than a 3-500? If not, then it seems to me that the 3-500 is a much better deal cost wise, even if it has to be replaced more often than the two higher priced tubes.

[K4ICL]

If cost is the issue, go for the 3-500ZG tubes. Much cheaper to run in the long run.

AL

[w5rkl]

I've looked around a bit but can't find expected life spans of these tubes;

3-500zg
3cx1200a7
3cx1500/8877

My concearn is the 3-500zg is so much cheaper than the 8877. Due to costs, does the 8877 last three or more times longer than the 3-500zg? Which tube is better with the life expectancy/cost factor?

Any amplifier tube will last quite a while in a well designed amplifier as long as it is not abused! A 3-500zg, 4-400, 4-1000, 811A, or 572B can be blown within a very short time in the hands of an inexperienced operator.

The 8877 filament must be allowed to heat up for several minutes before applying plate voltage. The 8877 filaments are coated with a gas absorbing coating and if plate voltage is applied before the warm up period has occurred, arcing can occur resulting in destruction in the tube. The glass envelope tubes such as 4-400, 3-500Z, 811A, 572B, and 4-1000 do not required long filament warm up periods. The plate is coated with gas absorbing coating, Zirconium and the tube's plate, during normal operation, should show a dull red color.

I recommend you read W8JI's website

http://w8ji.com/Amplifiers.htm

for a more details discussion of amplifier tubes.

73s
Mike
W5RKL

[k4zmi]

You know, everyone has had some really great information. But apparently no one can answer my questions the way I asked them. I am not asking for direct comparison between different tubes.

With proper operation, and without thinking about any other tube, how many hours will the 3-500zg last?

With proper operation, and without thinking about any other tube, how many hours will the 3cx1200a7 last?

With proper operation, and without thinking about any other tube, how many hours will the 8877 last?