[SixClub] Amplifier Questions...

[KB0NLY]

I found some in the Mouser catalog that should work ok... The physical size 
in the datasheet and a set of calipers tells the story.

73,

Scott



--------------------------------------------------
From: "Jerry W9FS EN61" <six_club at comcast.net>
Sent: Friday, June 04, 2010 2:26 PM
To: "World Wide Six Meter Club" <sixclub at mailman.qth.net>
Subject: Re: [SixClub] Amplifier Questions...

> Be sure to check the size of the metal clad micas they gome in different
> physical sizes. You were correct in the 30 =  30pf.
>
> Jerry W9FS
> ----- Original Message ----- 
> From: "KB0NLY" <kb0nly at mchsi.com>
> To: "World Wide Six Meter Club" <sixclub at mailman.qth.net>
> Sent: Friday, June 04, 2010 1:17 PM
> Subject: Re: [SixClub] Amplifier Questions...
>
>
>> Thanks for the details!!
>>
>> Mica, that's what I couldn't remember... I'm not dumb just memory
>> challenged... Yes metal clad mica's, found them in the catalog.  Boy I
>> wish
>> my memory worked.
>>
>> Because of which I'm printing off your email so I remember how to set the
>> bias when I get there... HI HI
>>
>> 73,
>>
>> Scott
>>
>>
>>
>> --------------------------------------------------
>> From: "Steve Katz" <stevek at jmr.com>
>> Sent: Friday, June 04, 2010 12:18 PM
>> To: "World Wide Six Meter Club" <sixclub at mailman.qth.net>
>> Subject: Re: [SixClub] Amplifier Questions...
>>
>>> See some stuff below...
>>>
>>> 73 de 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 9:45 AM
>>> To: World Wide Six Meter Club
>>> 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.
>>>
>>>>>Unless you lift the transistor tabs off the PC board, you can't make
>>> any real determination like this.  If you want to non-destructively
>>> (avoiding overheating) lift the tabs, loosen the bolts holding down the
>>> transistors, first (not remove them, just loosen them a bit so they're
>>> not tightly binding the transistors to the heatsink below them).  This
>>> way it will take less heat to reflow the solder and lift the tabs.
>>>
>>> 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?
>>>
>>>>>Those are mica capacitors without any outer covering, and without any
>>> leads; you could replace with high-Q RF ceramics (NPO) which will also
>>> usually work.  Yes, the caps around Q7 and Q8 are 30pF and 40pF.
>>>
>>> 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.
>>>
>>>>>Lift L7 from the base connection of Q7 and adjust the 100 Ohm bias pot
>>> for Q8 to idle at 150mA; then re-connect L7 to the base of Q7 and adjust
>>> its bias pot for a total idling current of 300mA.  It can be a bit
>>> higher, e.g., 200 and 400mA or whatever (very little power there either
>>> way).  The idea is to make them "equal."  Obviously, this is with no RF
>>> drive applied!!
>>>
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>>
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