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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 26th Nov 2019, 9:41 pm   #1
Steve G4WCS
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Default Cybernet PTBM121D4X modification ?

Refitting a pair of dc switching transistors and noted that the track from IC3 pin9 to T4 appears to have been deliberately cut. I wonder if it was in an attempt to make the power output across the bands less peaky as T4 contains a tuned circuit, and it has had a pll track cut at one time to take it onto 10M. Anyone come across this . No mention in the export service manual that its a factory mod ?
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Old 27th Nov 2019, 2:13 pm   #2
Techman
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Default Re: Cybernet PTBM121D4X modification ?

I don't know, but here's one I scrapped earlier - well perhaps 35 years ago
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Old 27th Nov 2019, 2:21 pm   #3
Steve G4WCS
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Default Re: Cybernet PTBM121D4X modification ?

thank you- no track cut there. Ill reinstate it and see if it makes any difference to the output
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Old 27th Nov 2019, 4:22 pm   #4
Steve G4WCS
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Default Re: Cybernet PTBM121D4X modification ?

Got this reply on a cb forum. So not a factory mod but my hunch was correct

A common mod to get more TX tuning bandwidth on the 121 is to cut the trace to the centre tap on T4 and solder a jumper from the track to the outer unused pin, I just last night rebuilt a Hygain V from a scrap board and did the cut track to T4 and replaced R150 for a 3k3 resistor and power on SSB is much better balanced across the three bands.
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