[Amps] Cheap auxiliary amp cooling

[Roger]

On 3/30/2012 11:08 AM, Vic K2VCO wrote:
> I often wonder why so many amplifiers are designed so that the full ZSAC flows when the
> user isn't actually transmitting. I always install a circuit in my QSK amplifiers which
> cuts off the plate current when the key is not closed.
>
> This applies to VOX or PTT voice and data modes, too, although the heat reduction there is
> smaller. A 3-500Z that is idling at 3kV with ZSAC of 100 mA is dissipating 300 watts just
> sitting there!
>
> I know that RF-drive operated circuits to do this are 'controversial' to say the least (I
> wouldn't ever use one for either CW or SSB),

My commercial amp uses EBS on CW break-in just fine and when using VOX 
on SSB.

I really don't like the idea of using the PTT line though as I tend to 
hang onto the mike while EBS would save a lot of heat.
OTOH I don't consider 300 watts a lot of power compared to the over 1000 
that Jim was talking about.

AND I view just placing a fan on top of amps with more than a bit of 
suspicion.  At the least I'd have the fan blowing up, not down.  The 
case might be hotter but the tubes should be cooler. Still as some one 
else said to the effect, don't have the extra fan blowing against the 
air flow as many of them end up doing.
Just because the cabinet is cooler doesn't mean the tubes are.

73

Roger (K8RI)