Valve Circuits (Battery) B3
1. Heptode Mixer
The 1R5 may be used as a self oscillating mixer up to about 20MHz or as a mixer with an external oscillator as shown here.
As with any multi-
The pentode mixer below has a much lower noise factor.
10n decoupling capacitors will be fine for the HF bands but must be increased in value for lower frequency bands like the medium and long wave bands.
2. Pentode Mixer
This mixer uses a 1L4 sharp cut-
A DF97 will provide a similar performance but with less stray coupling between the filament and anode because the suppressor grid is not connected to one side of the filament and may be grounded.
T2 is a bifilar wound transformer using a ferrite core. The reactance of each winding at the lowest oscillator frequency should be several times the impedance looking in to the filament.
Page under development
Results: An anode tuned circuit at 3.4MHz was chosen with an initial L/C ratio that provided a gain as a grounded filament/cathode amplifier of x20 (C2 = 100pF). The circuit was then configured as the mixer above with cathode injection and results measured from the high impedance input to the high impedance output. As expected the 1L4 (sharp cut-
Valve |
Signal Freq MHz |
Oscillator Freq MHz |
Oscillator Injection |
Conversion Voltage Gain |
1T4 |
9 |
12.4 |
1.2v pk- |
x8 |
1T4 |
21 |
24.4 |
1.2 v pk- |
x6.7 |
1T4 |
29 |
32.4 |
1.0v pk- |
x6.7 |
1L4 |
29 |
32.4 |
1.0v pk- |
x12 |
DF97 |
29 |
32.4 |
1.0v pk- |
x14 |