[Amps] 2xGS35b on HF

[Geert PA3CSG]

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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