[NLRS] Killed my amp? Probably

[KB0NLY]

If you have the 310 and not the 110 then you got dead finals... Adding 
jumper cables and crap before it to reduce the SWR to match the input is 
only making up for the high swr on the input do to the finals going south. 
Been there done that with a few of these RFC's.  I got a VHF in here a while 
back that seemed to make ok power output, about 150w with 45w of drive but 
the input SWR was around 2:1, put new finals in it and everything was right 
as rain.

I would also check the input matching however, make sure its not just a bad 
cap.

73,

Scott KB0NLY


-----Original Message----- 
From: David Palm
Sent: Thursday, September 03, 2015 4:12 PM
Cc: NLRS List ; Badger Contesters
Subject: Re: [NLRS] Killed my amp? Probably



Unfolding saga -- now I see I'm wrong.  I don't have a 4-110, I have a
4-310 which should take up to 30 watts of drive.  So I'm well under that
limit, but last night I watched the output of this amp fall off as I was
key down and now it's only putting out 30 watts for 17 watts in.

I'm also seeing a bit of SWR -- not huge, but noticeable -- when I put the
amplifier in line.

Any other ideas on what to check on this dude?  I've got it open on my
bench.

73,

David  W9HQ


On Thu, Sep 3, 2015 at 3:51 PM, Barry Malowanchuk <ve4ma at shaw.ca> wrote:

>
>
> Better RF Parts or else you may get a Chinese copy
>
> Barry VE4MA
>
> ----- Original Message -----
> From: "Dr. Gerald N. Johnson" <geraldj at netins.net>
> To: nlrs at mailman.qth.net, "Badger Contesters" <
> badgercontesters at mailman.qth.net>
> Sent: Thursday, September 3, 2015 2:00:06 PM
> Subject: Re: [NLRS] Killed my amp? Probably
>
>
>
> RF Parts probably also has the part.
>
> For the future you need to attach a cable to the amp input with 1.25 dB
> loss so the 20 watts from the 897 is only 15 at the amp. That's just a
> few feet of RG-58. ARRL handbook chart shows 12 or 13 dB / 100 feet off
> the top of the graph though. So ten feet should be pretty close. And the
> driver probably is bad.
>
> 73, Jerry, K0CQ
>
> On 9/3/2015 11:58 AM, David Palm wrote:
> >
> >
> > OK, time to tell on myself.  I was checking out my gear last night.  222
> > MHz ampflier is working fine and playing well with the transverter 
> > there.
> > So good to go.
> >
> > On 432 it's a different story.  Here's what you get when you don't use
> > stuff for a long time and forget when you have.  I connected the rig to
> the
> > amplifier, an RF Concepts 4-110.  I had long forgotten that this amp can
> > only take a max of 15 watts input.  My FT-897 puts out just over that.
> So,
> > I was keying the amp and getting about 80 watts out, which is actually
> > rather low, especially with that much drive.  But then as I watched, the
> > output just started dropping before my eyes, until I basically am 
> > getting
> > little to no amplification at all.
> >
> > I presume that I burned out the driver stage.  The schematic says that
> this
> > is an MRF646.
> >
> > Those of you who know about such things, does my diagnosis seem correct?
> > And do you know of any better source to get an MRF646 than this guy, who
> > has them for $20 apiece:
> >
> http://www.ebay.com/itm/Motorola-MRF646-/281687443775?hash=item4195e1493f.
> > Hopefully this will not be a big problem to swap out and be back in
> > business.  If you've done such things before and have some good advice,
> I'd
> > love to have it.
> >
> > Doh!
> >
> > 73,
> >
> > David  W9HQ
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