[Amps] Question about GS-35b efficiency

[David H Craig]

    I see you found pragmatism (real-world) trumps "specs".  My in-use 6m 
GS35b is 55% efficient, measured "old method" with 4400vdc on the plate & 
<150-vdc drop full-load.  57% (including power added), with just .550 amp 
plate current.  Oh well, so much for the spec sheet (remember that 
issue?)...  Bottom line, the GS35b tube is under-rated for B+... But no, 
can't be, right, huh????  Oh, yeh, BTW, my idle current in .200 amps as 
well.

    Dave N3DB


----- Original Message ----- 
From: "Bill, W6WRT" <dezrat1242 at yahoo.com>
To: "Amps reflector" <amps at contesting.com>; "RF Amps reflector" 
<rfamplifiers at yahoogroups.com>
Sent: Thursday, December 17, 2009 11:13 PM
Subject: [Amps] Question about GS-35b efficiency


>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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