If you want to build an amplifier using a tetrode but don't want to mess around with screen and grid powersupplies
the G2DAF concept is for you!
HV and filament voltage required, just as in a grounded grid amplifier. However, the screen (G2) voltage is derived from the input RF and the grid (G1) is at DC ground.
Check the circuit description below.
However, since a few years I have converted the amplifier to a normal tetrode amplifier with fixed voltages on G2 (900 Vdc) and G1 (-105 Vdc). This did not significantly change the performance of the amplifier, it just made it a little easier to drive. The G2DAF configuration worked flawlessly for >15 years. But as always, at some point I get the urge to change things - just because.... :-)
The shack, my QBL HF amplifier to the right. The bottom panel hosts the PSU for filament, screen and grid voltages for this amplifier. Above that is a 4CX350a amplifier for 144 MHz and at the top my modified LK-450 HF amplifier
The QBL 5-3500 tube
Check some detailed pictures, circuit diagram and tube specs
|Anode compartment||Anode plus tank circuit 160-10 mtrs|
|Anode compartment 1||Anode plus tank circuit, side panel view|
|Anode compartment 2||Anode plus tank circuit, top view|
|Bottom view||Input circuit, relay pwr supply, screen bypass|
|Screen bypass 1||Screen (g2) PTFE sandwich bypass, close view|
|Input||Input PI-network, relays switch different bands|
|Input 1||Input PI-network plus input resistors|
|Schematic diagram||G2DAF style QBL 5-3500 schematic diagram|
|Input circuit, coils||Schematic of input circuit using 9mm dia coils with trimmer cores|
|T/R switching||T/R switching using RJ-1A relays|
|QBL 5-3500 specification sheet||PDF with all tube data. (1Mb)|
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