General question on blown finals

[nosaj]

For example I have a Stryker sr440 radio on a dummy load and a wattmeter showing maybe 10watts. Should be showing 55 watts at least.
Do finals burn out, short out or just get weak? or all of them?
If they just get weak what should I see on a transistor tester out of circuit?
Trying to get a feel for what I should be seeing.
Thanks,
Jason

[jessejamesdallas]

sounds like one maybe blown...one I had did close to 60w

[nosaj]

So how can a blown final still put out 10 watts? Is it like a blown speaker that still puts out sound?
I had a kenwood that had a shorted final in it that kept blowing fuses removed the final and radio boots up , just waiting on replacements.

nosaj

[jessejamesdallas]

I think the 440 has two finals...mosfets...Never heard of finals going weak, like tubes...they either work, or don't.

[nosaj]

And they don't look like much fun to take out.

nosaj

[MDYoungblood]

The SR-440 does only have one final shown in the pic.

I would guess that it is blown and the only thing showing wattage is the driver (it can make up to about 10w itself), someone probably turned it up trying to get more out of the radio. These radios were made to produce swing wattage with gobs of modulation, not to be a powerhouse high wattage continuously radio.

3's

Greg

[nosaj]

This one is the mosfet version using 2 irf520, really cheap priced outputs. It did not occur to me the drivers could produce wattage through a blown final. I will keep this in mind on future repairs.

Thanks,
Jason

[jessejamesdallas]

The SR-440 does only have one final shown in the pic.

I would guess that it is blown and the only thing showing wattage is the driver (it can make up to about 10w itself), someone probably turned it up trying to get more out of the radio. These radios were made to produce swing wattage with gobs of modulation, not to be a powerhouse high wattage continuously radio.

3's

Greg

Think that is a pic of the first-run 440's like I had...One big monster final...I believe later they changed them, maybe when the 447's came out.

[MDYoungblood]

This one is the mosfet version using 2 irf520, really cheap priced outputs. It did not occur to me the drivers could produce wattage through a blown final. I will keep this in mind on future repairs.

Thanks,
Jason

Sorry I had never seen one using IRF520, the pic is of the older model like JJD said. The transistor was used in several high end ham radios (in pairs to produce 100w), they could handle extreme SWR but not overdriving.

3's

Greg

[nosaj]

I'll take a pic of it. It was throwing me for a while cause I was given a glossy foldout schematic with the radio that did not match the output. I was able to find the correct one on CBtricks I think it is the latest schematic.
But you did teach me that wattage can come from the driver through a blown final.
Thanks,
nosaj