160m Mods

160m Mods. The 160m mods involve working on:

1. the input PI section fig.1-4.

2. the PA output PI section fig. 5-8

3. removing one of the bandswitch stops fig.9

It's a tight fit inside the input circuit compartment. Facing the front, the 160m variable coil is mounted on the left side next to the 80m coil. The fixed coil and SM caps are tucked inside the semi closed aluminum box.

NB. It appears there are two different 30S1 input circuits depending on the age of the 30S-1 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. This mod does not deal with the double sided grounding wafers for obvious complex fabrication reasons. The wafers used in the 30S-1 are 45 degree type, next to impossible to find. The bakelite material is old and very easy to fracture. Utmost care is necessary to prevent breakage. The alternative is to make new blanks with FR40 board material a time consuming proposition.

Collins uses 1KV ceramic disk capacitors for the other bands, ideally the 160m capacitors should be 1 KV SM but space is tight. The 500V SMs showed no leakage up to 1.5KV, and should be ok up to 100W 3-1 SWR. Alpha 77Sx uses compression silver micas, which have higher Q than ceramics.

Fig.1 160m input-Pi circuit and L, C elements

The C values are 800pf, 1200pf, 1600pF. Start with these as there could be small changes depending on SWR. (I had to guess the input Z of the 4CX1000A).

L values are 4.2microH (adjustable), and 2.8 microH wound on a ferrite strip with leads.

Fig.2 input-wafer has dummy tabs that need to be removed

Fig.3 input-wafer with dummy tabs drilled out

Fig.4 VNA showing S11 for 160m input-circuit Zload=50 Ohms

The L, C values were adjusted for min SWR. 160M mods require an extra L and an extra C to cover the bandwidth, just like the 80m PI circuit.

Fig.5 Schematic showing 160m additions to the PA

PA Plate location is to the right, antenna to the left; this to reflect the actual band settings as observed from the rear. A cutout of the mounting bracket is necessary to make room for the 80m tab. Tabs are 0.023" thick.

Fig.6 Clearing a path to the rear PA band wafer for removal

extra text here

• PA-Wafer. Adding 80m and 160m tabs
• 
• 

It appears that the 80m and 160m tabs are connected, but they are not.

Fig.7 ordinary wafer used for 160m PA vacuum relay switching

extra text here about the PA choke mods and spurious resonances.

Fig.8 160m 160m PA vacuum relay

Jennings F4B-26S is a 26V pulsed DC latching relay with two 7 Ohms coils, one coil for turning ON and the other for turning OFF. A pair of 555 timers could be set up, but they require additional power sources. Still investigating a simple relay circuit that converts ON, OFF states to momentary ones. Any suggestions?

Fig.9 One band switch stop gets drilled out

One of the two band stops is drilled out to yield a 160m position. That's the hole closer to the center shaft. With the RF deck mounted on the PS cabinet, the stop to be drilled out is at ~11:30 o'clock. The other stop at ~6:30 is left alone. In this image the RF deck is laying on its left side. The 30S-1 band knob will point downwards for 160m.