Softy 1 - Page 9 - UK Vintage Radio Repair and Restoration Discussion Forum

ortek_service · 15th Mar 2021, 12:33 am

The UM1111 modulator these use are (in the words of Ambit, later Cirkit) rather crude (I looked inside one I've got, and it just seems to be a single transistor oscillator), with narrow bandwidth only suitable for low B/W B&W signals and prone to freq. drift / load-pulling. It's also design to run off a higher 6.5V etc rather than usual 5V regulated supply (although it seems they did on the Softy)

However, Chris has apparently tried one he managed to but with his new replica board and it does work on the same TV he tried.
So unless the one on Derek's board is on a frequency that the TV won't lock to, then it seems a bit strange that it wasn't possible to tune to it.
Unfortunately these early modulators have the adjustment trimmer on the underside, and original Softy PCB doesn't have an adjustment access hole for in-situ setting (that strange unknown board I bought with one on, does have with mod-wire etc. on modulator supply input)

ChrisOddy · 15th Mar 2021, 10:06 am

I'm afraid I don't know which part of the 4503 was faulty and its now on its way back to Derek.

As Owen says my replica board fitted with a UM1111 worked fine and with a UM1233. The TV I used is not particularly modern (~20 years) just a cheap and cheerful portable that was accessible. The RF signal from Dereks UM1111 was on frequency it just couldn't produce a picture ?

Chris

15th Mar 2021, 12:33 am	#161
ortek_service Octode Join Date: May 2018 Location: Northampton, Northamptonshire, UK. Posts: 1,440	Re: Softy 1 The UM1111 modulator these use are (in the words of Ambit, later Cirkit) rather crude (I looked inside one I've got, and it just seems to be a single transistor oscillator), with narrow bandwidth only suitable for low B/W B&W signals and prone to freq. drift / load-pulling. It's also design to run off a higher 6.5V etc rather than usual 5V regulated supply (although it seems they did on the Softy) However, Chris has apparently tried one he managed to but with his new replica board and it does work on the same TV he tried. So unless the one on Derek's board is on a frequency that the TV won't lock to, then it seems a bit strange that it wasn't possible to tune to it. Unfortunately these early modulators have the adjustment trimmer on the underside, and original Softy PCB doesn't have an adjustment access hole for in-situ setting (that strange unknown board I bought with one on, does have with mod-wire etc. on modulator supply input)

15th Mar 2021, 10:06 am	#162
ChrisOddy Pentode Join Date: Jan 2021 Location: Northampton, Northamptonshire, UK Posts: 131	Re: Softy 1 I'm afraid I don't know which part of the 4503 was faulty and its now on its way back to Derek. As Owen says my replica board fitted with a UM1111 worked fine and with a UM1233. The TV I used is not particularly modern (~20 years) just a cheap and cheerful portable that was accessible. The RF signal from Dereks UM1111 was on frequency it just couldn't produce a picture ? Chris