Hi Benny & list,
I use a 2 X GS31 amp on HF.
With 100W of drive you will see around 2kW. I run them in parallel with
the grid grounded. Well below tube spec!
I did worry about input impedances in the beginning but forgot what is
was... It is pretty close to 50 ohms for sure as on some bands I don't
need the build in antenna tuner of my rig. Not much thinking plain
building :-) And it saves alot of switching and stuff
Some pics:
http://pa3csg.hoeplakee.nl/joomla25/index.php/rf-construction/87-hf-amplifier-2-x-gs31
These are old pics. I replace the roller inductor because of too many
parallel capacitances to ground and replaced it by a switched coil.
Regards,
Geert PA3CSG
Benedikt Sveinsson schreef op 4-4-2014 18:02:
Hi amps specialists
As a side project I have been building a HF amplifier.
I have successfully built a GS35b 70cm amplifier, I have a big external
power supply (1,5A ICAS @4kv) that I previously built.
I was going to build a GS35b 2m RX1AS style, but decided on going for a
SSPA as my K3 that I use for EME can only output 10w, so driving the amp
would need a separate driver amp and I just went for the SSPA and that is
near completion.
I bought some GS35b¹s in Friedrichshafen last summer and I have sockets
etc...
And for some more back story - the idea was to buy a GU84 or similar
tetrode for the HF amp, but I wanted to build the tank first and see if I
could indeed build the damn thing. Now I think I have the tank fully built
- and I started contemplating just putting a single GS35b in as I have
some around.
What about 2x GS35B¹s ?
Has anyone here done that ?
What is the input impedance of the two tubes ? (scarse info available) (I
have a WD7S input board that he mailed to me by mistake, I will pay you if
I decide to use it! ;)
I imagine it being a helluwa high power amp - but good for 48 hrs
contesting doing 1.5Kw (not imagine driving it hard!)
What would be the drawback on using two tubes - I read somewhere don¹t use
two tubes, use a bigger one!
There is a considerable investment in a GU84/GU78 with a proper socket -
and I¹m worried about stability of a high gain tubes - (do I have to?)
73, Benni TF3CY
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