[Amps] GS23B Plate load resistance for HF

[Dave Trainor]

Yes I agree and that is what has me guessing, I don¹t have a load line for
the tube in HF service and since efficiency is a input value I don¹t know
if 50% or 60a5 or some other number is correct and that affects the plate
load resistance for Pi-L design.  Seems a lot of folks here are saying
that it won¹t achieve the efficiency of the Eimac¹s and that¹s OK with me
since I have these and they were cheap, I guess my electric bill will be
about 10% higher but I¹d need to use up a lot of electricity to break even
in cost.  I suppose what I need to do is use the middle %55 and then do
some testing, the caps should have enough range and since I am making my
own tank coil the cost of making more than one is not large, as long as
the %55 gets me in the ballpark.

73 - Dave N8ZFM





On 10/31/13, 5:02 AM, "Ian White" <gm3sek at ifwtech.co.uk> wrote:

>
>>>
>>>Using a spreadsheet I got from G3SEK. I am using the following values,
>>3000V
>>>on Anode, max of 1A DC anode current and planning on getting 1500W
>>output,
>>>using a K factor of 1.5. So the implied efficiency is 50% and a plate
>load
>>>of 2000 Ohms, all well and good but 50% seems low and I would think I
>>would
>>>be closer to 60%.
>>
>
>To Dave:
>The spreadsheet does NOT predict the efficiency the tube. In that part
>of the spreadsheet, efficiency is an INPUT value that you provide, and
>its accuracy is only as good as your personal guess.
>
>The "K factor" is widely touted as a method of estimating RL, the
>optimum load impedance that the Pi- or Pi-L network must offer to the
>tube. But the whole method is very dubious because it claims to be
>generic... as if all tubes were the same, which they very obviously
>aren't!
>
>That is precisely why the spreadsheet recommends that RL is estimated by
>drawing load lines on the  characteristic curves for the specific tube.
>The "K factor" method is a very inferior alternative.
>
> 
>To Bill:
>>
>>For what it's worth: I have built two amps using the GS35b and had the
>>same
>>low efficiency you indicate above. Several European hams have reported
>>the
>>same. It appears that 50% is all the tube is capable of. If you can
>tolerate
>>that, otherwise it works well and is very inexpensive. Going to a much
>more
>>expensive tube gains you only about 10%.
>>
>>As to what causes the low efficiency, I can only guess. I suspect the
>grid
>>structure does not have complete control over the electron flow and
>allows
>>some current to "leak" past it. That's just a guess, I am willing to
>stand
>>corrected if someone has a better answer.
>>
>>73, Bill W6WRT
>
>There is a major difference between the Western high-mu triodes and the
>Russian family of low-mu triodes.  High-mu triodes like the 8877 are
>designed to deliver good gain and efficiency at relatively low anode
>voltages, but the GS35b requires much higher voltages. Performance at
>anything below 3.0kV is sure to be disappointing, and the best overall
>performance is generally obtained at about 3.5kV on load, rising closer
>to 4.0kV off-load. Some specimens will tolerate higher voltages but with
>a rapidly increasing risk of arcing.
>
>
>73 from Ian GM3SEK
>
>
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