Leak Stereofetic, tuning wandering - UK Vintage Radio Repair and Restoration Discussion Forum

chiilyuk · 26th Jun 2022, 2:23 pm

I've finished recapping the PSU of a new to me Leak Stereofetic tuner and it works very well, though it has a habit of wandering off station over about 5 minutes after turn on.

I know a little bit about radios, but not enough to realign.

I wondering whether this simply something like the the PSU settling down as the set warms up and I would need to re-set the PSU voltages after a few minutes of on time, or whether it could be a component fault.

When on station the tuner sounds lovely, through a Radford STA15 and a pair of 57s...

Radio Wrangler · 26th Jun 2022, 4:00 pm

The wandering won't be fixed be realignment. Something is drifting and changing. Components in the local oscillator are first up for suspicion, also the grounding wiper contact on the tuning capacitor may be happier after a clean (everyone forgets it!)

Some LO capacitors may have been carefully chosen for special temperature coefficients to counter the drift of others.

David

snowman_al · 26th Jun 2022, 4:55 pm

Hi Chiily,
Did you see this post https://www.vintage-radio.net/forum/...83&postcount=3 ?

Service info here https://www.audioservicemanuals.com/...service-manual

Alan

McMurdo · 26th Jun 2022, 5:28 pm

you are engaging the AFC after you've found the station aren't you? Otherwise they will drift as they get warm.

AFC off > tune station > AFC on.

chiilyuk · 26th Jun 2022, 10:03 pm

Quote:

Originally Posted by snowman_al

Hi Chiily,
Did you see this post https://www.vintage-radio.net/forum/...83&postcount=3 ?

Service info here https://www.audioservicemanuals.com/...service-manual

Alan

Alan,

Thanks for the pointer. I had read elsewhere that the PSU voltages were critical and the PSU caps under spec for the voltage, especially if the bulb fails. With that thought, I have replaced all the caps in the PSU, including the trimmers (so black with age). Though I will re-check the voltages and ripple once it has warmed up and the signal drifted a little.

I also replaced C98 with a 22uf Tant as recommend on this forum, though I can't find the post now.

chiilyuk · 26th Jun 2022, 10:04 pm

Quote:

Originally Posted by McMurdo

you are engaging the AFC after you've found the station aren't you? Otherwise they will drift as they get warm.

AFC off > tune station > AFC on.

Do you know I don't think I am. I shall give it a go. Thanks for the info

chiilyuk · 30th Jun 2022, 1:40 pm

After about an hour of being turned on I checked the PSU voltages. Both the 9V and -5V rails were spot on, about 10mV out and ripple was no more than 2.5mV on both supply rails..

The AFC does work quite well and maintains the lock, though I think I need a better aerial than a length of stripped coax for better sound quality.

Trevor · 30th Jun 2022, 2:31 pm

Nice one I used to sell the Stereofetic a good tuner but critical re supplies In my opinion much better than the troughline Where I live the troughlines are not selective enough but to fair their were maybe only 3-4 channels when they were made

26th Jun 2022, 2:23 pm	#1
chiilyuk Triode Join Date: Dec 2021 Location: Thornbury, South Gloucestershire, UK. Posts: 30	Leak Stereofetic, tuning wandering I've finished recapping the PSU of a new to me Leak Stereofetic tuner and it works very well, though it has a habit of wandering off station over about 5 minutes after turn on. I know a little bit about radios, but not enough to realign. I wondering whether this simply something like the the PSU settling down as the set warms up and I would need to re-set the PSU voltages after a few minutes of on time, or whether it could be a component fault. When on station the tuner sounds lovely, through a Radford STA15 and a pair of 57s...

26th Jun 2022, 4:00 pm	#2
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,897	Re: Leak Stereofetic, tuning wandering The wandering won't be fixed be realignment. Something is drifting and changing. Components in the local oscillator are first up for suspicion, also the grounding wiper contact on the tuning capacitor may be happier after a clean (everyone forgets it!) Some LO capacitors may have been carefully chosen for special temperature coefficients to counter the drift of others. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

26th Jun 2022, 4:55 pm	#3
snowman_al Octode Join Date: Dec 2018 Location: Llandeilo, West Wales, UK. Posts: 1,092	Re: Leak Stereofetic, tuning wandering Hi Chiily, Did you see this post https://www.vintage-radio.net/forum/...83&postcount=3 ? Service info here https://www.audioservicemanuals.com/...service-manual Alan __________________ Never Leave Well Enough Alone...

26th Jun 2022, 5:28 pm	#4
McMurdo Dekatron Join Date: Jun 2009 Location: Staffordshire Moorlands, UK. Posts: 5,273	Re: Leak Stereofetic, tuning wandering you are engaging the AFC after you've found the station aren't you? Otherwise they will drift as they get warm. AFC off > tune station > AFC on. __________________ Kevin

30th Jun 2022, 1:40 pm	#7
chiilyuk Triode Join Date: Dec 2021 Location: Thornbury, South Gloucestershire, UK. Posts: 30	Re: Leak Stereofetic, tuning wandering After about an hour of being turned on I checked the PSU voltages. Both the 9V and -5V rails were spot on, about 10mV out and ripple was no more than 2.5mV on both supply rails.. The AFC does work quite well and maintains the lock, though I think I need a better aerial than a length of stripped coax for better sound quality.

30th Jun 2022, 2:31 pm	#8
Trevor Octode Join Date: Aug 2006 Location: Stoke-on-Trent, Staffordshire, UK. Posts: 1,082	Re: Leak Stereofetic, tuning wandering Nice one I used to sell the Stereofetic a good tuner but critical re supplies In my opinion much better than the troughline Where I live the troughlines are not selective enough but to fair their were maybe only 3-4 channels when they were made