Jim,
Recycling the basic RF deck from an HF amp carcass seems like a great way to
start on a homebrew HF amp project. Your amp looks great. Well done!
Paul, W9AC
----- Original Message -----
From: "Jim W7RY" <w7ry@inbox.com>
To: "Ulf (SM0NOR)" <ulf@sm0nor.com>
Cc: "AMPS" <amps@contesting.com>
Sent: Sunday, December 12, 2010 4:39 PM
Subject: Re: [Amps] PI-L Thoughts!
> The tank coils and the band switch is from Ten-Tec. They used this in the
> Titan 425. The tune-load knobs and Jackson Brothers drives are from them
> too.
>
> The 4th switch deck is to control the band switching relays on the WD7S
> tuned input board. I don't remember how I switched the large tune cap
> into
> the circuit but if you look at a Titan 425 schematic, you will see.
>
> You will also notice a large string of orange caps mounted on a piece of
> perf board and connected to the lager tune cap. This is the 160 meter tune
> padder. These are 33 PF 6KV caps from Mouser. The caps are all in parallel
> of course.
>
> Thanks for all the kind words!
>
> 73
> Jim W7RY
>
>
>
> --------------------------------------------------
> From: "Ulf (SM0NOR)" <ulf@sm0nor.com>
> Sent: Sunday, December 12, 2010 12:49 AM
> To: "Jim W7RY" <w7ry@inbox.com>
> Subject: Re: [Amps] PI-L Thoughts!
>
>> Hi Jim,
>>
>> Really nice work!
>> How did you switch in the larger cap? I see you have a three deck switch.
>> One would go to the input network, one to the Pi and and to the L.
>>
>> Carefully scrutinising your pictures it looks like you actually added a
>> fourth deck. In that case I understand how you did it.
>>
>> 73's
>> Ulf
>>
>> Sent from my iPad
>>
>> On 12 dec 2010, at 04:35, "Jim W7RY" <w7ry@inbox.com> wrote:
>>
>>> Please look at the way I handled a low minimum value cap in my 3CX800
>>> amp. I used a small cap for 10, 15 and 20 meters. Then switched in a
>>> larger cap for 40, 80 and 160.
>>>
>>> Pictures @
>>>
>>> http://s900.photobucket.com/albums/ac206/w7ry/3CX800%20Amplifier/
>>>
>>> 73
>>> Jim W7RY
>>>
>>> --------------------------------------------------
>>> From: "Ulf (SM0NOR)" <ulf@sm0nor.com>
>>> Sent: Saturday, December 11, 2010 10:26 AM
>>> To: <Amps@contesting.com>
>>> Subject: [Amps] PI-L Thoughts!
>>>
>>>> Hi all,
>>>>
>>>> I'm looking for some advice regarding the tank.
>>>>
>>>> I'm about 2/3 on the way to complete my first amplifier build and I'm
>>>> having some thoughts about how to get C1 to low enough to load on 10
>>>> meter.
>>>>
>>>> To no surprise the 25-300 pF capacitor measured a min of 40 pF when
>>>> mounted in the RF deck. This will give me trouble on the higher bands.
>>>> I
>>>> know this is discussed a lot in the literature, but I'd like your
>>>> thoughts on one specific solution.
>>>>
>>>> The obvious solutions are to either get another C1 with a lower min
>>>> capacitance or to get a vacuum variable. Maybe I could do the first
>>>> solution, but that would probably make it necessary to rebuild the
>>>> switching section with another deck to be able to switch in different
>>>> sections of a split stator cap. The vacuum solution is really easy, but
>>>> I have not really budgeted for that.
>>>>
>>>> This makes me think of a third solution mentioned in the handbooks but
>>>> not really discussed in depth; and that is to tweak the Q to make it
>>>> work. And I would like to have the opinions of all you experienced
>>>> builders out there!
>>>>
>>>> Here are my calculations (based on one of the handbooks)
>>>>
>>>> C1 C2 L1 Q
>>>>
>>>> 160 330 1400 30.4 11
>>>> 80 174 716 14.1 12
>>>> 40 96 388 7.2 12
>>>> 20 43 182 3.9 11
>>>> 15 45 161 1.7 16
>>>> 12 43 151 0.7 18
>>>> 10 43 143 0.6 20
>>>>
>>>> For simplicity I did not add the values for L2 in this post.
>>>>
>>>> Ok, what do you think of this? Is it Ok with a Q of 20 on 10 meter? I'm
>>>> using 5 mm copper tubing in the 10-20 coil. Or would it be better with
>>>> one of the other solutions? Tweaking the Q is by far the most simple
>>>> solution given the components I already have.
>>>>
>>>> Thanks for any advice!
>>>>
>>>> By the way..... the build is based on a GU74B and I'm aiming for a
>>>> 1KW
>>>> PEP.
>>>>
>>>>
>>>> 73's
>>>>
>>>> Ulf (SM0NOR)
>>>> ulf@sm0nor.com
>>>>
>>>>
>>>>
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>>>>
>>>>
>>>>
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>>
>>
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