[SixClub] Amplifier Questions...

[Steve Katz]

Comments in general about this kind of amp:

I've worked on a lot of these.  The transistors can and do fail.  But
many other things fail that can create "zero output:"

-Bad relay at RY2 or RY3 (or just bad contacts on them)
-Solder connections that became so hot at Q7 and/or Q8 that the solder
crystallized and became an open or nearly open circuit (in these cases,
re-heating and removing all existing solder, then re-soldering with new
solder -- and doing it correctly -- can actually bring a "dead amp" back
to life)
-Open or shorted capacitors, many locations
-Open, burned or disconnected RF chokes at L7, L8, L9...

The list is long...

73

Steve WB2WIK/6


-----Original Message-----
From: sixclub-bounces at mailman.qth.net
[mailto:sixclub-bounces at mailman.qth.net] On Behalf Of KB0NLY
Sent: Friday, June 04, 2010 10:22 AM
To: World Wide Six Meter Club
Subject: Re: [SixClub] Amplifier Questions...

There is no output...

Some more specifics... it's a 10w input 100w output amp.  Driving with
10w 
there is ZERO output.  I think the driver, an MRF646 might also be bad.

There is no measureable output with even an RF Probe.

73,

Scott



--------------------------------------------------
From: "Peter Chase" <pdcn1j at msn.com>
Sent: Friday, June 04, 2010 11:55 AM
To: "6meter club" <sixclub at mailman.qth.net>
Subject: Re: [SixClub] Amplifier Questions...

>
> Just check the input to each final and compare it to its output.  You 
> should have a notable  increase at the output of each .  You should
look 
> up the RF device so you know what to expect for power output and what
the 
> normal parameters are.  this can be done with basic test equipment.
Hope 
> this helps.
>
> Regards
>
> Pete N1JHF
>
>> From: kb0nly at mchsi.com
>> To: sixclub at mailman.qth.net
>> Date: Fri, 4 Jun 2010 11:45:27 -0500
>> Subject: [SixClub] Amplifier Questions...
>>
>> I know this is OT, but there is a lot of smart cookies on here and
the 
>> other
>> reflectors I have tried, like the AMPS reflector just don't get any 
>> replies
>> like here...
>>
>> Questions..
>>
>> 1. I have a UHF amp I'm working on, a RF Concepts 4-110. I think the
>> finals are bad, but need someone to verify my bad memory. When
testing
>> these bipolar transistors the collector-base and base-emitter
junctions
>> should test as a diode correct? I have a dead short from base to 
>> collector
>> so that seems to verify they are fried. And the emitter-collector has
to 
>> be
>> open in both directions, well of course its not because of the dead
short 
>> to
>> the base.
>>
>> 2. It's been a while since I worked on a solid state amp... Whats the
>> package type of the small capacitors used on the finals, those little

>> square
>> metal jobs with a tab out of one side. For the life of me I can't 
>> remember
>> the package number so I can go catalog search for some new ones, as
I'm 
>> sure
>> they need replacement after the heating they took on removal. Also,
the
>> marking on them, in this case 30 and 40, I believe that's in pF
correct?
>>
>> 3. This amp has a bias adjust for each transistor, what is the best
way 
>> to
>> adjust the bias after replacing the transistors, just set for minimum

>> idle
>> current or is there a number I should be shooting for? No specs
available
>> from RF Concepts unfortunately but I was able to actually find a one
page
>> schematic at least.
>>
>> 73,
>>
>> Scott
>>
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