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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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13th Mar 2021, 11:48 pm | #1 |
Triode
Join Date: May 2016
Location: Corbridge, Northumberland, UK.
Posts: 18
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Pye Westminster Low Transmit Audio
Hello
I'm hoping someone out there has an old Pye Westminster, the old dash mount W15FM would be ideal. I picked one of these up from a local club a few years ago, crystalled up for six useful channels. I've come to re-commission it and found that whilst it receives OK, the modulation (deviation) is very low. The microphone output is fine and has been compared to another microphone, but the output from the Transmitter AF Unit (10) on pin 1 is about 800mV peak-to-peak when whistled. This is then connected to pin 7 on the Modulator Driver (12) - the mic amp input. L1 and L2 are the two associated cores which would normally need peaking but mine have seized so may need adjustment or may be perfectly OK. The RF output is bang on 10W in the high power position. What I need to know is, is 800mV p-p feeding the Modulator Driver, at full whistle, enough to provide full deviation, or do I need to remove and free / replace L1 and L2? The manual tells me how to set the max deviation as required, but doesn't tell me the expected p-p audio reading required at the Modulator Driver input. Maybe someone could pop the cover off their Wessie and pop a scope on the mic input, then whistle loudly into their microphone and let me know what the p-p voltage is please? It would be much appreciated. Thanks, Simon M5POO, Corbridge |
14th Mar 2021, 6:21 pm | #2 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,953
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Re: Pye Westminster Low Transmit Audio
Are you using the right microphone?
There were 2 different ones, one for AM and one for FM; the audio response differed (one had a rising response with frequency, the other a falling response: get the wrong one and you'll lose out against the TX pre-emphasis). It was generally accepted that FM Wessies tended to under-deviate - presumably a design-feature to stop overdeviation when an irate taxi-driver bellowed some choice terms about other motorists. It's possible to add a decoupling capacitor across one of the low-level-audio transistors' unbypassed emitter resistor to get a bit more 'oomph'. |
15th Mar 2021, 12:06 am | #3 |
Triode
Join Date: May 2016
Location: Corbridge, Northumberland, UK.
Posts: 18
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Re: Pye Westminster Low Transmit Audio
Yes, it's the correct microphone. When I say the deviation is low, I mean VERY low...much less than would be caused by the wrong mic. Running tests with a pal, he initially thought there was no audio. Unless someone knows off hand, I'm hoping someone can pop the top off their radio and measure that peak to peak voltage for me. It really would be a great help.
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15th Mar 2021, 6:47 pm | #4 |
Triode
Join Date: Oct 2018
Location: Halesowen, West Midlands, UK.
Posts: 24
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Re: Pye Westminster Low Transmit Audio
Have you followed the mic audio coax cable from the mic socket to the TX audio board then on the the audio input to the modulator driver? Some W15's were modified for an external 5 tone selcall box and had a 15 way D socket on the back for an interface, links fitted if not used.
If yours is modified could this be where the audio is lost. Just a thought Paul |
16th Mar 2021, 2:04 pm | #5 |
Triode
Join Date: May 2016
Location: Corbridge, Northumberland, UK.
Posts: 18
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Re: Pye Westminster Low Transmit Audio
Hi Mascot-22. Yes, I've checked everything...all I need is someone to measure the peak to peak voltage. Thanks for the suggestion but PLEASE everyone, I just need this simple measurement that will take five minutes to do. Everything else on the radio is as it should be. Cheers, Simon.
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16th Mar 2021, 10:57 pm | #6 |
Triode
Join Date: May 2016
Location: Corbridge, Northumberland, UK.
Posts: 18
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Re: Pye Westminster Low Transmit Audio
ALL SORTED THANKS...I've managed to find the information I needed.
Simon |
16th Mar 2021, 11:11 pm | #7 |
Nonode
Join Date: Dec 2012
Location: Stockport, Greater Manchester, UK.
Posts: 2,085
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Re: Pye Westminster Low Transmit Audio
Simon - don't leave without telling us the answer
__________________
- Julian It's good here |
21st Mar 2021, 1:47 pm | #8 |
Triode
Join Date: May 2016
Location: Corbridge, Northumberland, UK.
Posts: 18
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Re: Pye Westminster Low Transmit Audio
Well Julian, although these radios seem to bring daft prices occasionally, no one on this group seems to have one. It's surprising how little information there is on the internet too. I rang someone who I remember modified dozens of these for fellow hams...and he told me the answer immediately. He said I needed &^%^%£$" mV...sorry, QRM there. It was enough for me to fix the problem. I'm going to put a post on my website soon, so it would be a shame to replicate the information here But if anyone has the same issue, they can always send me a DM. 73, Simon M5POO.
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