For Sale..New 2 meter GS-31B amplifier.

[VK3ZL]

Hi all...I have finally completed the new 2 meter GS-31B amplifier I mentioned in a previous thread..

This amplifier uses a GS-31B Russian triode in Grounded Grid mode.,I have used a new custom built Toroidal multi tapped HT transformer and the standing HT is around 3500vdc...I also used a new custom made 12.6 volt Toroidal filament transformer which has a multi tapped primary allowing selection of correct filament voltage for different mains voltage..The relay supply uses a new multi tapped transformer and an LM317 voltage regulated rectifier system providing 24 volts for the bias relay and two changeover relays...The amplifier cooling system uses a 4.5 inch fan blowing straight into the sealed cathode compartment directly on to the tube filament cathode and exhausting through a small grid on the side cover..

The main cooling has a 12-28 volt Papst 285cfm fan...This runs off a separate 20 volt power supply..The top RF deck is sealed from the cathode deck....Air passes through the GS-31B cooler up through a Teflon chimney exhausting through the top cover...Air flow and cooling is excellent..The main cooling fan can be switched off manually so that the filaments can be left running when the amplifier is not in use....This allows for switch on of the main cooling fan and HT and relay supply when you need instant use..

The amplifier is just coasting at the 400 watt VK ham power limit and is also suitable for those who have a high power permit for EME use..

I have installed an input relay and a coaxial output relay on the amplifier...However for those who wish to use an external preamp relay system and sequencer I can re do the system with a direct N type socket in and out...The bias idle relay can then be activated via the switch line from the exciter..

The amplifier uses a W4ZT bias board...I run a bias control adjustable from the front panel...Amplifier idle current can be adjusted for CW or Linear mode....Plate and Grid current are metered and function lamps for 24vdc, and Operate, as well as a mains indicator on the front panel....HT, Filament and Main cooling Fan have separate switches with neon indicators.
I have run all the usual tests on the amplifier into a 1kw dummy load and all functions work correctly..

The amplifier uses an adjustable T input network on the drive input...The Plate Tuned Circuit has adjustable Tune and load capacitor...Loading is set for best operation into your antenna system...I have set it up and locked it using a 50 ohm Bird 1kw dummy load, but into your antenna system it may have to be slightly adjusted if the vswr is different than purely 50 ohms..Once set it is locked and needs no further adjustment unless your antenna resistance is changed..Tune is smooth and peaks nicely..

The amplifier is all hand made using all new components..Contact me if you need more detailed information Email or phone 0355791403....Thanks....Bob..VK3ZL..

[VK6OX]

Another fine example of Bob's expertise!

[VK3ZL]

Hi all,just an update and answers to a few phone queries from two weeks ago...I have been occupied with CFA comms work with the Kentbruck fires...Trevor VK5NC came over this morning and we spent a couple of hours running tests etc on this amplifier...Using a Bird watt meter and dummy load we spent some time fine tuning the amplifier for best results...With 25 watts of drive the amplifier produces 560 watts of output way past the VK 400 watt power limit...We didn't try for maximum output...Running minute's long tests the amplifier runs cool at that power output..I used my infra-red thermometer to measure the center core pin of the GS-31B tube at the 560 watt power level and it gets no warmer than 80C, actually 79.6C after 2 minutes of continuous carrier..The tube shows the rated 13db gain.Circuit efficiency is good..

At 560 watts power output Anode current is 380ma...Grid current 145ma..HT under load is a tad over 3Kv..The amplifier is only coasting at this level.. Drive VSWR is dead flat 1-1..Through VSWR is 1-1..

I will probably list this unit on ebay in the next few days..

Bob..VK3ZL..

[VK3ZL]

This amplifier is now listed on ebay Item Number 160978641903..

Bob..VK3ZL..

[VK3ZL]

Hi all..This 2 meter amplifier still for sale Ebay item 160986691611...I am open to a reasonable offer for this amplifier and will include a spare new tube with it..

Bob..VK3ZL..

[VK3ZL]

Hi all...This amplifier didn't sell...I am putting it in mothballs for the time being...If anyone is interested in buying it contact me and we can discuss price shipping etc...

73...Bob..VK3ZL..