|[AMRadio] Ranger... good news, bad news|
jcandela at prodigy.net
Sun Nov 5 15:38:36 EST 2006
Gary Schafer wrote:
> If the tubes glow in an SB200 you are running them too hard.
Roger but it is a good reference point. If it just starts to redden
after 5 mins, I consider this acceptable and time to shut up anyway.
Reply by Jim C:
Actually since linear AM efficiency doubles at 100% tone modulation, the
tubes will stay cooler the louder you talk. It's the resting carrier with no
modulation that makes the tubes blush the most. The exception is controlled
carrier modulation where the drive is cut back in the absence of voice
A SB-200 is good for 100 to 130 watts RF output (carrier only) on AM.
This amount on top of a ranger output is way less than 1 S-unit, and
overdrive is a big problem. Replace that SB-200 with a SB-220 and the story
changes considerably where 350+ watts (carrier) are available with AM. With
the SB-200 you have 2 X 160 watts (ICAS) dissipation available whereas with
the SB-220 you have 2 X 500 watts (CCS) dissipation available. Figure 30-35%
carrier efficiency, and the capabilities of each amplifier are quite
The power supplies and air cooling methods require you to de-rate the
theoretical capabilities of the tubes when running AM. Talking at a high
average level (don't splatter) will cool the tubes some, but the power
supply don't care if the load current produces power in the form of heat, or
additional RF output power during modulation..
I wonder if those out there using Heath linears on AM have anything to add
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