[AMRadio] WTB SB-220

Jim Candela jcandela at prodigy.net
Sun Sep 26 19:02:20 EDT 2004

    It seems that the plate modulator type hams look down at those running AM Linears! It would be interesting to run the numbers to look at heat radiated into the hamshack for say a globe king 500 pumping out  350 watts carrier, and a SB-220 putting out the same, and driven from something like a Heath DX-60 with the carrier control removed. We all know both would heat the shack considerably. How much more though from one over the other?? I'm talking about total heat dissipated including filament power, bleeder resistors, plate dissipation, etc.
    Now for that 6 DB that is not detectable. When listening to a signal under marginal conditions at the threshold of being copyable, that extra S unit or about 6 DB is huge.
I'd say let Cory run his amplifier, and maybe chip in a suggestion or two on how to maximize the linearity, and stability of the setup. For example a audio feedback loop from the SB-220 RF out (add a detector circuit) to the modulator audio chain to straighten out the trapezoidal pattern as seen on a scope. The linear won't be perfectly linear, so this technique if done well can really help clean up the signal and reduce bandwidth by reducing the distortion products.
   BTW on my QRO 20A project I am doing just that to linearize the single EL-34 output tube which runs AM linear AB1 mode to provide 10 watts RF carrier output. A 6DB reduction in audio gain from the feedback has a considerable effect on the modulated envelope (matches the low level waveform much closer) and increases the maximum PEP power some for a given amount of gain compression.

RJ Mattson <rjmattson at hvi.net> wrote:
If your Viking II runs 100 watts, 400 watts will give you about 1 s-unit
gain. Not even detectable unless you look at the meter.
Could be helpful during the winter months as a supplemental room heater.


----- Original Message ----- 
From: "Cory Hine" 
Sent: Sunday, September 26, 2004 2:13 PM
Subject: [AMRadio] WTB SB-220

> Hey gang,
> I am looking for a Heathkit SB-220 to run about 300 watts on AM using the
Viking II to drive it. Does anyone have a decent amp that they want to sell?
I would like pics if possible.
> Thanks,
> Cory/AD5QP

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