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M4000 Amplifier

kb6led

Member
Apr 11, 2009
92
7
18
Does anyone by chance have any info on this amplifier such as a schematic diagram? I have a resistor getting hot, the unit still puts out power but obviously has an issue. I have been over to CB tricks but nothing listed as just a M4000.

Thanks
 

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Ok it's in the top right hand corner I put a small red arrow next to it, Thanks
 

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Looks like it's part of the keying circuit, or the preamp. I'll try to see what value it is. Thanks for posting the pics!

(edit) Does the preamp and the keying circuits function as normal? Or do they act strange?


~Cheers~
 
Preamp works fine but sometimes in the ssb mode once and a while it will just hang. the resistor starts to over heat when I am on ssb. I guess a good test would be turn off the delay and see what happens.
 
Off topic a bit what would be a realistic output expectation on an linear that has 4 MRF454’s like this one has I looked up the specs of the MRF454’s and they look to be rated at 80 watts each. I use to have one just like this in the early 80’s but don’t remember what that one did. I don’t know where the manufacture came up with the stated output power printed on the front face.. 400AM PEP 750 SSB PEP those numbers make no sense to me.:confused:
 
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Off topic a bit what would be a realistic output expectation on an linear that has 4 MRF454’s like this one has I looked up the specs of the MRF454’s and they look to be rated at 80 watts each. I use to have one just like this in the early 80’s but don’t remember what that one did. I don’t know where the manufacture came up with the stated output power printed on the front face.. 400AM PEP 750 SSB PEP those numbers make no sense to me.:confused:


350-400 watts peak on AM sounds right. I had a 4 pill Messenger 350 that was within that range with the 454s in it.
Not a chance that amp will do anymore than 400 watts pep on ssb.....750 is hillarious!
 
looks like the transistors have been changed to mrf454 .
I have that exact amplifier although no in as nice condition.
here is what they should be.
 

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Wow! did you get yours new like that? If so the one I have must have been downgraded for whatever reason. If its not to much trouble could you tell me the color code off the resistor in yours that is smoked in mine? Also while your in there a could u take a photo of the entire board? That would be helpful.

You are welcome to email it to: KB6LED (AT) AOL.COM


Thanks
 
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You will find different transistors as the date of production changed, this is common in many of these old amps.
The output numbers on any of the 70`s/80`Ten meter Mono band solid state ( read gray market CB ) amps are way over rated.


73
Jeff
 
My guess these where probably made in someone’s garage or shop and if they had a problem getting transistors they stuffed the linear with what was available at the time, but that is just a guess on my part. but them over rating them at a dollar a watt sales price = big $$$
 
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