[Amps] Building an Amp 101
akozak at hourglass.com
Sat Jan 18 10:52:30 EST 2014
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.
From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Jim Garland
Sent: Saturday, January 18, 2014 10:41 AM
To: amps at contesting.com
Subject: Re: [Amps] Building an Amp 101
Re Model 86 vs. Model 88 bandswitches: I used a model 86 on my homebrew 8877 amp (4700V on the plate), but after flashing it over, I upgraded to a model 88. With a six position bandswitch, the model 86 should work fine up to at least 5 kW or so, provided that a progressively shorting wafer is used. The problem is that when one adds the WARC bands more positions are needed, which rules out a single wafer progressively shorting switch.
My homebrew amp worked fine until I added the WARC bands. Initially I swapped out my 6 position model 86 shorting switch for an 11 position non-shorting model 86 switch, and immediately had flashover problesm because of the high RF voltages induced on the floating unused inductor segments. I swapped in an 11 position non-shorting model 88 and haven't had any problems, though I'm not really happy with the solution.
To my knowledge, nobody has yet figured out a convenient way to bandswitch a nine-band QRO amplifier, without either using a roller inductor or complicated multi-wafer bandswitches (check out the bandswitch in the Drake L7, for instance). Commercial moderate power amps, like the Alpha 9500, do it by using bandswitches with 20 degree indexing, but the contact spacing is too small to make them suitable for larger amplifiers.
> -----Original Message-----
> From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Bill
> Sent: Saturday, January 18, 2014 4:52 AM
> To: amps at contesting.com
> Subject: Re: [Amps] Building an Amp 101
> It might handle the current but the spacing is too small for a proper
> voltage rating. It should be about four inches in diameter and if
> bought new should cost between $300-$400. Check out these:
> The model 86 is the minimum you should use and the model 88 is optimum
> for your power level.
> 73, Bill W6WRT
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