[Amps] Building an Amp 101

[Jim Garland]

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.
73,
Jim W8ZR




> -----Original Message-----
> From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Bill Turner
> 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:
> http://multi-tech-industries.com/rswitches.html
> The model 86 is the minimum you should use and the model 88 is optimum
> for your power level.
> 
> 73, Bill W6WRT
>