[Amps] Mobile Amps

Sun Jul 31 14:34:04 EDT 2005

Will... I think you missed the point.  If designed correctly, there is 
absolutely no reason for an adjustable capacitor in the output circuit.  It 
must be a comfort thing... some folks can't seem to get away from knobs to 
play with.

Sincerely,

Dr. William J. Schmidt, II  K9HZ
Trustee of the North American QRO - Central Division Club - K9ZC

Email: bill at wjschmidt.com
WebPage: www.wjschmidt.com

"If computers get too powerful, we can organize them into a committee; that 
will do them in."  -- Bradley's Bromide

----- Original Message ----- 
From: "Will Matney" <craxd1 at verizon.net>
To: <amps at contesting.com>
Sent: Sunday, July 31, 2005 10:16 AM
Subject: Re: [Amps] Mobile Amps

> David,
>
> The air variable is used in the output tuning. I've seen some use fixed 
> capacitance here and a step up using a mica compression cap. However, in 
> these large ones, I've seen many burn out. What some of the guys started 
> doing was making a piston type cap out of two pieces of brass tubing with 
> a piece of teflon sheet wrapped around the inner tube to insulate it. They 
> then slide it in and out to tune it. The ones they do this way are really 
> made kind of rough plus take up a lot of room. I always liked using an air 
> variable here and never had the problems. The smaller amps used either 
> fixed caps, which your limited on being able to tune, and or compression 
> mica trimmers where you can tune them. They just wont hold up on an amp 
> this size. This would be the cap in paralell with the secondary of the 
> output transformer, or on this amp, right after the combiner. The rest of 
> that amp looked like the others that's being built though.
>
> It's hard to see on the pic, but the RF keying circuit is wired together 
> by the parts leads in mid air and soldered. That's what I refered to 
> earlier as a rats nest. It's located right at the antenna relay. The best 
> I could see from the pic, it didn't have any bias circuit, so it's a class 
> C amp. $900 is a little steep in price, but they are 16 transistors there 
> or 8 sets of modules if one wants to call them that. At say 150 watts min. 
> each set, that's 1200 watts, or probably a little more. I don't know of 
> any mobile amateur amps available that size. That wasn't why I posted 
> about this amp. It was really so folks to see how they were being made by 
> the pics.
>
> Best,
>
> Will
>
> *********** REPLY SEPARATOR  ***********
>
> On 7/31/05 at 9:55 AM Dr. William J. Schmidt, II wrote:
>
>>Will,
>>
>>I seen you discuss adding "air variables", etc. to the output circuits of
>>transistor amps before... and can't quite figure out why one would do
>>that.
>>I've built and converted many transistor amps in the past, and they all
>>used
>>a nice set of high quality wide-band transformers... and a good gain
>>leveling circuit that would cost just a few dollars.  Anyone that reads
>>the
>>handbook or Schoneke's book ("Single Sideband Systems")... should be able
>>to
>>design and build adequate transformers.  If its the antenna that's causing
>>an SWR problem... its probably better to fix the antenna than build a
>>pseudo
>>antenna match into the amp.
>>
>>I see the mentioned amp lacks any harmonic filters.  I *suppose* one could
>>argue that the antenna is the filter network in a mobile situation.
>>
>>Sincerely,
>>
>>Dr. William J. Schmidt, II  K9HZ
>>Trustee of the North American QRO - Central Division Club - K9ZC
>>
>>Email: bill at wjschmidt.com
>>WebPage: www.wjschmidt.com
>>
>>"If computers get too powerful, we can organize them into a committee;
>>that
>>will do them in."  -- Bradley's Bromide
>>
>>
>>----- Original Message ----- 
>>From: "Will Matney" <craxd1 at verizon.net>
>>To: <amps at contesting.com>
>>Sent: Sunday, July 31, 2005 8:28 AM
>>Subject: [Amps] Mobile Amps
>>
>>
>>> All,
>>>
>>> I ran across this solid state amp on ebay and thought it might be a good
>>> one to convert over to amateur service. I about bet now it's class C but
>>a
>>> bias circuit can be added. It doesn't have a good RF keyer in it either.
>>> However, the builder did add an air variable capacitor for output tuning
>>> which is a step up for most. This "Pac Man" brand is a name I've never
>>> heard of. From the pictures though, it looks like a good candidate
>>inside
>>> and that it may have enough room for a bandswitched filter board. If
>>your
>>> not interested in buying it, the pics give a good idea of what they look
>>> like on the inside. Also, this amp uses 8 sets of push-pull amps using
>>16
>>> transistors. In other words, it's a big amp.
>>>
>>> Link;
>>>
>>>
>>http://cgi.ebay.com/PAC-MAN-16-PILL-10-METER-AMP_W0QQitemZ5794298630QQcategoryZ48700QQrdZ1QQcmdZViewItem
>>>
>>> Best,
>>>
>>> Will
>>>
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>>>
>>
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>
>
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