We had one of those 1 kw Raytheon transmitters at WKOP in the early ‘60s and
the 833A modulators were class B. But the push-pull RF final pair of 833As was
class C.
Victor 4X6GP (ex K2VCO)
> On 1 Nov 2019, at 20:05, Ron Youvan <ka4inm@gmail.com> wrote:
> I have seen plenty of push-pull "Class B" RF amplifiers, being a worn
> out broadcast engineer. The Raytheon Company use to make low power am
> transmitters and they were superior to the common RCA and Gates units.
> The 250. Watt transmitters use two RCA 810 tubes (triodes) in push-pull
> "Class B" modulation amplifiers and two RCA 810 tubes in push-pull
> "Class B" AF amplifiers. For one kil-a-Watt transmitters they used two
> RCA 833 (triodes) in push-pull "Class B" modulation amplifiers and two
> RCA 833 tubes in push-pull "Class B" RF amplifiers.
> In the Raytheon transmitter these tubes had a reputation of lasting
> three years as the RF amplifier and when the emission was down they
> moved the modulators to the RF stages and installed new tubes in the
> modulator stage and got another three years.
>
> RCA and Gates got one year out of their parallel RF amplifiers.
>
> The reason we don't all use push-pull "Class B" RF amplifiers is our
> propensity for multiband operation. Before 1960 many hams had push-pull
> "Class B" transmitters that used a pair of RCA 811, 812 or 813 tubes and
> 1 kW B&W plug-in coil sets. (all grid driven with 100. W. B&W plug-in
> coil sets.) If there is any instability in a push-pull "Class B" RF
> amplifier they are easily "cross neutralized."
>
> All of our "rice boxes" use a "Class B" RF amplifier" as the final
> amplifier, driven by a beefie class "A" transistor.
>
> If you consider the amount of time the devices are idling, class "B"
> amplifiers are the overall most efficient linear amplifier that there
> is. Don't think two parallel devices is the same as a push-pull "Class
> B" RF amplifier.
> --
> Ron W4BIN - Understanding is much better than
> knowing how.
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