[Amps] Question about GS-35b efficiency

[Jim Barber]

And I'd like to hear more about expectations of what a single GS-35B
will do under in-spec operating conditions. Bill's numbers are in-spec 
at the edge of the published limits. My question has to do with how many 
hours can expect to get out of one run at those limits. I've heard 500 
hours - not enough!

The reason I ask is because I'm considering retiring/selling off my 
PA77's and spare 8877's due to age and high eventual replacement costs. 
The problem is - what to replace them with? 3-500's are the current 
price/performance kings and I already own a 3KA, but what new or newer 
3-500 amp performs in the same league as the PA77 or the 3KA? Then 
there's always the new solid-state stuff... The ALS1300 looks very 
tempting at the street price, but I wouldn't exactly put it in the same 
overall manufacturing quality category as the others mentioned here.

I may have just convinced myself that there's no "best" answer. I 
suppose to summarize I'm getting a bit nervous about long-term cost and 
availability of ceramic Eimacs, as well as *any* continued availability 
of Russian surplus tubes. Perhaps an 'elite class' solid-state amp will 
appear somewhere on the market?

Solid-state... Admittedly 'biased' gut reaction: Blech! Oh wait... Maybe 
they're actually biasing those things these days. ;-)

73,
Jim, N7CXI


Bill, W6WRT wrote:
> I have a question about the plate efficiency of a GS-35b amplifier.
> 
> I have built two of them for 160-10 meters, and while they worked ok, the
> efficiency was not as good as I expected. In both cases I ran them at 3 kVDC and
> in order to get a full 1500 watts out, had to drive them to 1000 mA plate
> current. That equates to about 50% efficiency, which seemed a bit low. 
> 
> In both cases, I removed the GS-35b and replaced it with an 8877. With no other
> changes except bias diode and heater transformer, I was able to get 1500 watts
> out with only 830 mA plate current, an efficiency of 60%. I swapped two
> different GS-35b's with the same result. Both were brand new tubes. Results were
> essentially the same on all bands, with a slight drop off on 15 and 10 meters
> with all three tubes. 
> 
> With all of the different tubes, I set the bias for a ZSAC of about 200 mA.
> 
> I have spoken to two European hams and one US ham and they have reported similar
> results.I wonder if the GS-35b might achieve higher efficiency at higher plate
> voltages?
> 
>  I would appreciate hearing from anyone who has made similar measurements.
> 
> 73, Bill W6WRT
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