[Amps] Using 813 tubes on 17 meters and above...

[Joe Subich, W4TV]

On 12/2/2017 10:12 AM, Peter Bertini wrote:
> Plate load for two is around 3500 ohms, so I'll be around 1750 or so
> with four of the beasts in parallel...
Plate load is determined only by Plate voltage, peak current and class
of operation.  The plate load will be no lower with four tubes than
with two tubes unless you are able to drive the four tubes to a higher
total current.

Do your calculations based on *total* current drawn.

73,

    ... Joe, W4TV


On 12/2/2017 10:12 AM, Peter Bertini wrote:
> I'm getting serious about building an 813 amp as winter project and need
> some input from other OT's who've played with these tubes on 17 meters and
> above.
> 
> Plans are to go with three or four tubes in parallel.  Power transformer is
> rated 1500va and I'll be near 2.8 kV plate voltage, in grounded grid.
> 
> Plate load for two is around 3500 ohms, so I'll be around 1750 or so with
> four of the beasts in parallel... which is doable using a Pi L on 80 and
> 160 to keep the load capacitor size reasonable, and then going over to a Pi
> Net for the upper bands.  I was more concerned with the combined plate
> capacitance, which is going to be close to 60 pF  ???  That is value is
> over the design value for a Pi Net with a reasonable Q at that load
> impedance.  I am still very curious how others have made out using two or
> three tubes in parallel on 17 meters and above. I've heard, anecdotally,
> that tapping the plate tune cap down on the tank coil helps, but I've not
> seen that in any published literature.  Any problems with using Amidon
> T255A-2 core for a combined shorted-turn inductor for 80 and 160 meters on
> the low Z side of a Pi-L,  and another core for the 160 meter inductor on
> the plate side of the Pi L?
> 
> Any advice?  By the way, I am going this way because I have plenty of NOS
> RCA tubes and sockets, and I can always change over to a more modern tube
> in the future.
> 
> 73
> 
> Pete
> 
> <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=icon>
> Virus-free.
> www.avast.com
> <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=link>
> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>