[Amps]  GS23B Plate load resistance for HF

peter chadwick g8on at fsmail.net
Fri Nov 1 04:16:42 EDT 2013


GS23B tetrode, not a GS35B triode.

What was the IMD on the 2 times GS35B amp?


Peter G3RZP

 Message Received: Nov 01 2013, 05:31 AM
 From: "Jim Thomson" <jim.thom at telus.net>
 To: amps at contesting.com
 Subject: [Amps]  GS23B Plate load resistance for HF
 Date: Thu, 31 Oct 2013 18:54:18 +0100
 From: peter chadwick <g8on at fsmail.net>
 To: TexasRF at aol.com, keepwalking188 at yahoo.com, dezrat1242 at yahoo.com,
 amps at contesting.com
 Subject: Re: [Amps] GS23B Plate load resistance for HF
 Assuming 3kV on the plate, 500 volts on the screen and AB1 operation in grounded cathode, I calculate a PEP output of 1540 watts, a dissipation of 1240 watts, efficiency 55% and a load resistance of 1570 ohms - calculation method as per RCA.  
 Peak plate voltage when loaded is 3700 volts.
 The 4CX1000A has a much bigger allowable plate swing  before the plate current curve starts to bend - which helps the efficiency.
 Peter G3RZP
 ##  are u folks talking about a GS23B..... OR  a GS35B ???      On a buddys  2 x GS35B  6M amp,  we managed to get 5 kw out on 50.125 mhz  with  225 watts of drive  from a FT-2000. 
 He could easily bury the slug past 5 kw.   At which point the  10 kw slug was inserted.  The FT-2000 is capable of 250w out on 6m.      Plate V  was aprx  4300 NO load on RX...... and   4150 vdc under load. 
 The 150 vdc drop consisted of a 100 vdc drop  from drawing 2A  of plate current  through the 50 ohm glitch Resistor.... + another  50 vdc  drop from the B+  supply.  I had him temp short out the glitch R..to see what the 
 real V drop was..... and it was only 50V.    But this was an oddball case where  a 253 lb dahl xfmr was used on one of its lower taps... + a  165 uf filter cap..and 2 ga wire back to the main 200A
 panel.   4150 x 2A = 8.3 kw    5000 /8300 =  60.24 % eff. 
 ##  carl is correct though.... the  GS35B is like a 4-1000.   Gain goes WAY up when you crank the B+ up.    On my old 4-1000 amps... I would get 600 w out with 2.5 kv under load + 120 w of drive.
 With 4.4 kv under load, and same 120 w of drive.... power increased to  1980 watts out.    Roller coil was optimized in each case to factor in the different plate load Z....and in both cases was tweaked 
 for a Q of 8-10  to maximize eff.     
 ##  4100-4300  under load on a GS35B  is  about the max you can use on a good tube.   Much above that..and you get into trouble. 
 Jim  VE7RF 
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