[Top] [All Lists]

Re: [Amps] HELP...2x GS35b

To: <>
Subject: Re: [Amps] HELP...2x GS35b
From: "DF3KV" <>
Date: Fri, 16 Oct 2009 23:58:38 +0200
List-post: <">>
Hi Jean-Pierre,

The output Z for 2 GS-35b will be about 850-900 Ohms at 3KV 2A.
You can´t drive the tube to an anode voltage of 0V, so you may only use the
voltage swing for your calculation.
The mode will be AB2 and that means a K of 1.6.
As Thomas mentioned you will need capacitors with very low C min, so better
use small capacitors and add padders for the lower band.
For optimum Q and shortest leads to the band switch you will need 3 or 4
The arrangement of tank components is quite critical, construct for shortest
possible lead length.
3 tube amps with 3xGS31 and 3xQB5/1750 have been built successfully with
almost same power and efficiency on all bands.
Probably you will need to use vacuum variables for small Cmin and high
circulating currents anyway, so you will be better off to mount them
vertically, which gives you less stray capacity.


> By means of those values I arrive by a load resistance of  693 ohm.(Ra= 
> Ua/Ia*K=1.87) like the formula tells

> Some guys told my that it is not possible to obtain a good tuning with 
> such low load resistance,in this case you have to use other LOAD filter 
> configurations instead of a simple classical PI-filter !!

No, that is no problem with a pi circuit

> - Some bands is it not possible to tune(21Mhz and higher not possible and 
> no L-coil anymore in circuit).
> - I  most of the time are both capacitors C1 and C2 totally turned open 

There is something totally bad, it might be difficult on the higher
frequencies of 10m but not already at 15m.

Amps mailing list

<Prev in Thread] Current Thread [Next in Thread>