[SixClub] Amplifier Questions...

Fri Jun 4 14:24:31 EDT 2010

Yep... I figured this amp would need a $100 or so in parts.  Hey it was a 
cheap dead amp that I knew would need repair so I'm happy.  I will have 
about $150-$200 into it total with parts and original purchase.

Last few of these on eBay went for $250-$300.

73,

Scott

--------------------------------------------------
From: "Steve Katz" <stevek at jmr.com>
Sent: Friday, June 04, 2010 1:20 PM
To: "World Wide Six Meter Club" <sixclub at mailman.qth.net>
Subject: Re: [SixClub] Amplifier Questions...

> You might need a new pair of MRF648s.  They're $48 each from RF Parts
> (ouch!)
>
> 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 11:15 AM
> To: World Wide Six Meter Club
> Subject: Re: [SixClub] Amplifier Questions...
>
> Thanks for the info!
>
> Checked the relay.. All is well there, probe shows rf into and out of
> the
> relay, and rf at the input of the MRF646 driver, little or no output
> from
> the driver.  Checked all the chokes and caps, nothing looks burnt
> either.
> All solder connections look good but I did reflow some just to be sure.
>
> Another anomaly is that the amp was drawing 10a with power applied,
> power
> switch off.  Lifted the Base of both finals and the current dropped to
> mA,
> so it appears the finals are shot no matter what, they are shorted from
> base
> to collector, tested after removing with VOM.
>
> Looks like I need to start ordering some parts..  I love a good fixer
> upper
> project!
>
> 73,
>
> Scott
>
>
>
> --------------------------------------------------
> From: "Steve Katz" <stevek at jmr.com>
> Sent: Friday, June 04, 2010 12:29 PM
> To: "World Wide Six Meter Club" <sixclub at mailman.qth.net>
> Subject: Re: [SixClub] Amplifier Questions...
>
>> 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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