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Receive transistor in amp - same/same?

Robb

Honorary Member Silent Key
Dec 18, 2008
11,432
3,651
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Silicon Valley CA, Storm Lake IA
20161001_134528.jpg

Working on a local op's 'King Bee 150/250' amp. The receive amp doesn't work; receive goes dead when switched on. What transistor is used? What substitutes can be used? Schematic for this amp available/link? Possible biasing mods?

Don't usually work on CB amps, just radios. Turned down the AM carrier to 2w to keep it from splattering. ANY/ALL info appreciated and welcome, as I can't seem to find much info at all about it.

Thanks.
 
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Let me post a pic of the inside of my Palomar amp that looks similar. The switches are different, but the case looks identical to the one I have. Might help. Not sure. But here are some pics to compare. Again, not sure this will help, but here goes.
 

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If you need more pics let me kmow. I tried to get as many as I could.
 

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Couple more, might be some repeats. Sorry if it doesn't help Robb. I tried man.
 

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Some more pics
 

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Last ones. Hope they might help.
 

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Don't know much at all about amps; so bear with me.

When the amp is off, I am seeing a 1 1/2 watt carrier loss thru it into the dummy load. IOW, 3w in to the amp, and 1 1/2w out of the amp when turned off. I'm sure this can't be correct.

BTW - what is the proper input power to mrf454's?
5w or 10w/each?

Took out the mrf454's and tested them. They tested OK with both the diode test and resistance test. Also not seeing anywhere near 200w out of it, so I am at a bit of a loss to figure out why this amp isn't working as it should.

What could be causing this? Bad relay? Bad coupling caps?
Again; working w/o a schematic has been difficult.

Also the original receive amp transistor is marked:
"034
MPS
5172"
So I have NO idea what part is in this thing.
Any ideas?
2N5172- maybe?
Translates to equivalent 2N2904.
Perhaps a suggestion for a replacement trans that has low noise/clean output?
Like a 2N5088?

blue_thunder_200_inside.jpg

BTW 2222DBFL, this pic is similar to the inside of this amp and your amp; could you take a closeup pic of the small transistor near the very front of your box (circled in red in the pic), and can you read the numbers on the face of it and its orientation? That may help me figure out what transistor I need to get this amp fixed and off my bench. Much appreciated!

Thanks
 
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10w drive should make about 200w output with a pair of 454's on 13.8v,

i have come across amps that have high vswr and attenuate your power in bypass mode, cp163's do it,
sometimes a trimmer cap from the bypass side of the relay to ground will tune out most of the mismatch.
 
Robb here is that part I think. The numbers on it are as seen on the pic below.
Part #
MPS2
222A
M594
This is the part number I see. I hope this is what you are speaking of. I am no amp expert by any means either!! Again, hope I got the correct part for you.
 

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10w drive should make about 200w output with a pair of 454's on 13.8v,

i have come across amps that have high vswr and attenuate your power in bypass mode, cp163's do it,
sometimes a trimmer cap from the bypass side of the relay to ground will tune out most of the mismatch.
Seeing about 1/2 that - about 100w on AM.
Transistors are out now and tested OK.
 
That bottom row of numbers may be different than what I posted. Hard to tell. Here is another close up pic of it.
 

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I'll see if I can find my magnifying glass and look closer at it as well. Give me a few as I am headed to the store now.
 

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