160m Mods

From Collins 30S-1 HF Amplifier
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160m Mods. The 160m mods involve working on: 1. the input PI section, 2. the PA output PI section. 160m components are highlighted in yellow fig 1. 3. changing one of the bandswitch stops.


It's a tight fit inside the input circuit compartment. 160m variable coil is bottom left. The other 160m coil and SM caps are tucked inside the aluminum box.

NB. It appears there are two different 30S1 input circuits depending on the age of the amp. The 160m mod is practical only for input circuits using simple wafers with contacts on one side only. If there is a grounding ring in addition to a selector ring then things get rather complicated. The mod I am doing does not deal with the double sided grounding wafers for obvious complex fabrication reasons.

Collins uses 1KV disk ceramic so ideally the 160m capacitors should be 1 KV SM but space is tight. I tested the 500V SMs i am using and they showed no leakage up to 1.5KV, the max range on the 576 Tek curve tracer, so they should be ok up to 100W. I noticed Alpha 77Sx uses compression micas, which have higher Q than ceramics.

Fig.1 Schematic showing 160m additions to the PA
Fig.2 160m addition to the input-Pi circuit


Accessing the rear PA band wafer for removal
160m new, added input-switch wafer
160m switch wafer with arrow
160m new, added vacuum relay
input-switch-wafer modifications for 160m
input-switch-wafer mods 2nd view, for 160m
VNA showing S11 for 160m input-circuit