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Ca346
Advanced Member
Username: Ca346
Post Number: 739
Registered: 8-2003
| | Posted on Friday, April 30, 2004 - 6:06 pm: | 
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I have been doing some research on replacement power transistors for my two amps. One is a GALAXY 350 with two 2SC2979's and the other is a COPPER KL-500 with four SD1446's. I was looking for a single replacement for the GALAXY 350. (No problem with the KL-500) But what I am finding is the suggestion that they be replaced in pairs or QUADS.
Can I replace a single transistor or should I replace both (pair) even though they both don't need replacement? |
Kc0gxz
Advanced Member
Username: Kc0gxz
Post Number: 782
Registered: 3-2003
| | Posted on Friday, April 30, 2004 - 11:54 pm: |
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Ca346
That's a very good question.
There is a lot of pros and cons concerning this. Years ago when all RF amplifiers were of the tube variety, it was the norm to replace all RF power tubes at the same time. Reason being, they usually slowly died at the same pace. And even back then, matched pairs of tubes were availible and sold as such.
Even today when buying solid state RF devices from sources that speciallize in them, you have the choice of buying them as individuals or as matched pairs. Matched Pairs (or more) are actually RF power transistors that have been picked and matched together because of their very closely matched tolorances with one another.
Buying a matched pair of RF trans always cost more because of the time consuming hand work that is involved of going through the stock and coming up with a matched or closely matched pair of transistors.
Some people don't even bother with buying matched devices. They just order what they need and be done with it. But as far as replacing both of them at the same time--YES. Personally, I never put a new one in an amp to work with an old one. They're not really that expensive. But either way WILL work.
Here's another way to look at this. Both headlights in your vehicle have been working fine for the last 4 or 5 years. All of a sudden one of them burns out. You replace it with a new one. Now you have one that seems to be brighter than the other.
Do you understand where I'm going with this? They both work. It's just that one headlight seems to be working a little better than the other. If it were my car and my amplifier, yes, I would replace both headlights and both power transistors.
Do I personally order "matched pairs"? Not on your life. Like me, many people could care less if they're matched or not. These are very inexpensive and inexpensively built amplifiers. They are far from being the BIG DOLLAR competition amplifiers that are out there.
I'm going to stop here before I confuse myself anymore than I already have and hope this post has helped you some. I'm sure you will be getting other opinions on this subject also.
73s for now 346.
Jeff, kc0gxz. |
Tech8541
Moderator
Username: Tech8541
Post Number: 176
Registered: 12-2003
| | Posted on Saturday, May 01, 2004 - 12:24 am: |
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it looks like kc0gxz and i have a difference in opinion on this matter. here is what i posted to this in the 'open forum' part of the copper forum.
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always try to replace the complete set (pair, quad, etc) as a 'matched set'. rf parts (www.rfparts.com) is the best place that i know of to get these 'matched sets'. matched sets help to guarantee that each trans is pulling its own share. non-matched sets can cause a serious unbalance where one trans is doing more than the other, which will lead to premature failure.
lets say that you have a 4 'pill' amp and one trans goes bad. it is best to replace all 4 with a matched set, but if you can't replace all 4, then replace the 2 'pills' that share 1 transformer. there is a combining system that will aid in balancing the output of each transformer. before this combining system there is nothing to balance the 2 transistors sharing that 1 transformer, so you need to use a 'matched pair'.
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