When I incorrectly imagined myself capable of building an
amp like this I discovered this site:
http://gs35b.com/gs35bvs8877.html
It contains an excellent charted and textually-described
explanation of the specs and practical applications of the
two - as well as a compare and contrast of the tubes.
Although the 8877 has higher "mu" it has a lower tolerance
for error.
I seem to also recall that tuned-circuit components that
work well with an 8877 may not function as efficiently with
s GS-35b due to different inductance and capacitance factors.
Of course I am the least-informed and experienced here ...
so please consider the link without my commentary and see
what the gathered wisdom here has to offer from their
hands-on experience!
73, doc KD4E
And, in case I forget, a blessed CHRIST-mas to all!
> 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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Thanks! & 73, doc, KD4E
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