Signal dropping - UK Vintage Radio Repair and Restoration Discussion Forum

Linnovice · 3rd May 2018, 11:46 am

Hi all, this is my first post on this forum so please be gentle if I ask dumb questions.
I have a Trio (read Kenwood) KT-5500 FM/AM Tuner which I’ve not used for a while. I connected it up this morning and have found that when tuned into a station it drops the signal. When I retune it the same station seems quite distance away from the original tuned position. There also appears to be a lot of rubbish stations between the two tuned positions. This is for Radio 3 and fluctuates between 90 ~ 92 MHz on the scale. It’s now been on for approx 2hrs and is now holding steady. I have a five element outdoor aerial at 12m from ground level aimed at Wrotham with a virtually full deflection on the signal strength meter. Can anyone point me in the direction of cause and cure please? I have moderate knowledge of circuits and soldering so hopefully it’s a repair I could make myself.

As an aside, the reason I’ve bought it back into service is to improve the signal going into my system and ultimately recorded on R2R Tape (the principal hobby). I’m comparing it with a Linn Kudos FM tuner that I have but I do think the older Trio produces a much better sound (when in tune that is). It seems much more natural and ‘alive’. The Linn is good and doesn’t drop the signal but to me it’s like comparing a glass of Harvey’s Bristol Cream to a nice single malt Whiskey 😁.

Anyway, back to the problem. Any advice would be very welcome.

HamishBoxer · 3rd May 2018, 12:02 pm

Yes,might be worth a gentle tap around in case of dry joints as a starter.

PS Stick with the malt!

G8HQP Dave · 3rd May 2018, 12:05 pm

If the audio disappears when you tune in correctly then this could be a problem with a mute circuit - which is supposed to do the opposite!

Finding several copies of BBC main stations is not unusual, although you would be more likely to get this when pointing north(ish) from the south; from just south of Birmingham I could pick up the northern transmitters when pointing at Sutton Coldfield. It could just be that your antenna is in a good position. Alternatively it could be due to intermodulation caused by too strong a signal.

Try adding some attenuation. If the extra signals just get a bit weaker then they may be genuine signals from distant transmitters. If they disappear then they may be intermodulation products from the front-end being overloaded by the local transmitter.

boxdoctor · 4th May 2018, 10:26 am

As this set has not been in use for some time, the earthing brushes on the tuning capacitor may have some oxidation or other contamination on them due to lack of use. A minimal spraying of them with a good switch cleaner may be all that is needed.
It could, as been suggested above, be excessive signal input. Using a random length of wire as a temporary aerial, or an attenuator, will help to confirm or eliminate that possibility. Tony.

3rd May 2018, 11:46 am	#1
Linnovice Hexode Join Date: Jun 2014 Location: Chelmsford, Essex, UK Posts: 386	Signal dropping Hi all, this is my first post on this forum so please be gentle if I ask dumb questions. I have a Trio (read Kenwood) KT-5500 FM/AM Tuner which I’ve not used for a while. I connected it up this morning and have found that when tuned into a station it drops the signal. When I retune it the same station seems quite distance away from the original tuned position. There also appears to be a lot of rubbish stations between the two tuned positions. This is for Radio 3 and fluctuates between 90 ~ 92 MHz on the scale. It’s now been on for approx 2hrs and is now holding steady. I have a five element outdoor aerial at 12m from ground level aimed at Wrotham with a virtually full deflection on the signal strength meter. Can anyone point me in the direction of cause and cure please? I have moderate knowledge of circuits and soldering so hopefully it’s a repair I could make myself. As an aside, the reason I’ve bought it back into service is to improve the signal going into my system and ultimately recorded on R2R Tape (the principal hobby). I’m comparing it with a Linn Kudos FM tuner that I have but I do think the older Trio produces a much better sound (when in tune that is). It seems much more natural and ‘alive’. The Linn is good and doesn’t drop the signal but to me it’s like comparing a glass of Harvey’s Bristol Cream to a nice single malt Whiskey 😁. Anyway, back to the problem. Any advice would be very welcome. __________________ Small Scotch, New Aids and Happy Ears

3rd May 2018, 12:02 pm	#2
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,935	Re: Signal dropping Yes,might be worth a gentle tap around in case of dry joints as a starter. PS Stick with the malt! __________________ G8JET BVWS Archivist and Member V.M.A.R.S

3rd May 2018, 12:05 pm	#3
G8HQP Dave Rest in Peace Join Date: Sep 2008 Location: Solihull, West Midlands, UK. Posts: 4,872	Re: Signal dropping If the audio disappears when you tune in correctly then this could be a problem with a mute circuit - which is supposed to do the opposite! Finding several copies of BBC main stations is not unusual, although you would be more likely to get this when pointing north(ish) from the south; from just south of Birmingham I could pick up the northern transmitters when pointing at Sutton Coldfield. It could just be that your antenna is in a good position. Alternatively it could be due to intermodulation caused by too strong a signal. Try adding some attenuation. If the extra signals just get a bit weaker then they may be genuine signals from distant transmitters. If they disappear then they may be intermodulation products from the front-end being overloaded by the local transmitter.

4th May 2018, 10:26 am	#4
boxdoctor Rest in Peace Join Date: Sep 2010 Location: Ripley, Derbyshire, UK. Posts: 785	Re: Signal dropping As this set has not been in use for some time, the earthing brushes on the tuning capacitor may have some oxidation or other contamination on them due to lack of use. A minimal spraying of them with a good switch cleaner may be all that is needed. It could, as been suggested above, be excessive signal input. Using a random length of wire as a temporary aerial, or an attenuator, will help to confirm or eliminate that possibility. Tony.