[Amps] Building an Amp 101

[Carl]

The Henry 8K Ultra uses solenoid contactors to select fixed caps in lieu of 
a bandswitch. The inductor is a rotary and a small vacuum cap is used for 
fine tuning, both motor driven with 10 turn pots or presets.

Carl
KM1H



----- Original Message ----- 
From: "Fuqua, Bill L" <wlfuqu00 at uky.edu>
To: "Al Kozakiewicz" <akozak at hourglass.com>; "MU 4CX250B" 
<4cx250b at miamioh.edu>
Cc: <amps at contesting.com>
Sent: Sunday, January 19, 2014 12:05 PM
Subject: Re: [Amps] Building an Amp 101


>   Most relays are not constructed of materials suitable for RF. Plastic 
> rather than ceramic is an example. They use a leaf spring material that 
> can handle current just fine at 60HZ or DC but it has a higher resistance 
> than copper. And since the current doesn't flow thru the entire cross 
> section, only on the few microns of skin depth the RF resistance is much 
> higher. To get the gap needed you would need open frame relays, which take 
> up a lot of space. I have had one surplus relay bandswitched amplifier 
> which used the open frame relays that used to be used as ladder line 
> antennas switching relays. But it was a very large box with a pair of 813s 
> in it.
>
> 73
> Bill wa4lav
>
> ________________________________________
> From: Amps [amps-bounces at contesting.com] on behalf of Al Kozakiewicz 
> [akozak at hourglass.com]
> Sent: Sunday, January 19, 2014 10:43 AM
> To: MU 4CX250B
> Cc: amps at contesting.com
> Subject: Re: [Amps] Building an Amp 101
>
> To make it clear, I've never tried this so I'm not speaking from personal 
> experience.
>
> But it seems logical to me that if a vacuum relay is required for the 
> voltages and duty involved, then a bandswitch is out of the question as 
> well, isn't it?  My thought is that, putting aside questions around 
> stray-L that might arise from the insertion of a relay, it's easier to 
> find a relay with sufficient contact spacing than it is to find a 
> bandswitch with a large enough diameter to maintain the same spacing 
> between contact elements.
>
> I guess these sorts of problems is why it's called engineering and not 
> science!
>
> Al
> AB2ZY
>
> -----Original Message-----
> From: MU 4CX250B [mailto:4cx250b at miamioh.edu]
> Sent: Sunday, January 19, 2014 9:32 AM
> To: Al Kozakiewicz
> Cc: amps at contesting.com
> Subject: Re: [Amps] Building an Amp 101
>
> Relays are certainly a possibility, Al, but for a nine band amplifier 
> things get a bit complicated. My latest project ( 90% completed) is a 
> duo - band 80m/160m amplifier with a pi- L tank circuit, and for that I am 
> using two DPDT vacuum relays, each of which cost over $100.
> Scaling that up to a nine band amplifier doesn't seem very practical or 
> cost-effective.
> 73,
> Jim w8zr
> Sent from my iPhone
>
>> On Jan 18, 2014, at 8:52 AM, Al Kozakiewicz <akozak at hourglass.com> wrote:
>>
>> Why not use relays appropriate for the switching duty?  Then the 
>> bandswitch can be just about anything or even remotely controlled.  Plus 
>> you can locate the switch where it's convenient to operate instead of 
>> being constrained by the necessity to place it close to the RF 
>> components.
>>
>> Al
>> AB2ZY
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