Hello
I have a Yamaha T-7 tuner that I resurrected (the storage cap for the presets failed and leaked all over the board, also most of the 25v 10µF caps had started leaking and corroded their own legs). Anyway it works but reception isn't that great unless I just hook up a wire to the other side of the balun filter that sits right next to the antenna input basically just bypassing it. One of the coils had a broken wire which I repaired, it did improve it somewhat but still not as good as should be. The two resonator caps across the windings seem to be very tarnished (silver mica ???) and I don't have the correct values to try and replace them. I found an article where they explain that there is a gain in doing the bypass properly but I don't really understand what exactly the steps are : http://www.audiocostruzioni.com/r_s/accessori/Yamaha T7 - tuner/Yamaha T7 - tuner.htm
They explain that there is a gain in doing this properly but I don't really understand what exactly the steps are
I have a Yamaha T-7 tuner that I resurrected (the storage cap for the presets failed and leaked all over the board, also most of the 25v 10µF caps had started leaking and corroded their own legs). Anyway it works but reception isn't that great unless I just hook up a wire to the other side of the balun filter that sits right next to the antenna input basically just bypassing it. One of the coils had a broken wire which I repaired, it did improve it somewhat but still not as good as should be. The two resonator caps across the windings seem to be very tarnished (silver mica ???) and I don't have the correct values to try and replace them. I found an article where they explain that there is a gain in doing the bypass properly but I don't really understand what exactly the steps are : http://www.audiocostruzioni.com/r_s/accessori/Yamaha T7 - tuner/Yamaha T7 - tuner.htm
They explain that there is a gain in doing this properly but I don't really understand what exactly the steps are
Silver mica small value capacitors are very reliable unless damaged .
What you are talking about is aerial (antenna ) impedance matching if the balun is faulty you could make another one,less than perfect impedance matching reduces the signal strength .
I made several aerial tuners for my communication receivers winding a large plastic tube with copper wire and soldering various inductance points to a switch .
But I take it nowadays everything is compact then get the inductance and wind a new one .
There are a whole variety of baluns so I don't know your type but yes you can bypass it but I had a look at your link so it looks iron core with various input tapping .
Question--- are all the inputs to the aerial circuit not working because of the faulty balun or do some work okay?
As a test touch the front section RF stage trimmer with your finger to see if the signal increases --just by the balun.
IF you have not completely removed any capacitor leakage film from components in the RF stage it will never work properly due to leakage at HF.
What you are talking about is aerial (antenna ) impedance matching if the balun is faulty you could make another one,less than perfect impedance matching reduces the signal strength .
I made several aerial tuners for my communication receivers winding a large plastic tube with copper wire and soldering various inductance points to a switch .
But I take it nowadays everything is compact then get the inductance and wind a new one .
There are a whole variety of baluns so I don't know your type but yes you can bypass it but I had a look at your link so it looks iron core with various input tapping .
Question--- are all the inputs to the aerial circuit not working because of the faulty balun or do some work okay?
As a test touch the front section RF stage trimmer with your finger to see if the signal increases --just by the balun.
IF you have not completely removed any capacitor leakage film from components in the RF stage it will never work properly due to leakage at HF.
I'm not sure it's silver mica but I heard a lot about "silver mica disease" in tuners and had to deal with it once in front end of a luxman. The surface was covered with black tarnish eating away through the insulation and causing all kinds of strange noises. The ones I see here also have that black tarnish although they look different. I can scrape it away with my finger but don't know what lies beneath.
Indeed I tried with a 75ohm basic T antenna and even on a strong station I had static and only average reception, I then just clipped a test lead on the other side of that balun coil and static was gone and signal strength way up (same happens if I touch the RF trimmer or clip my lead on there). I don't have a 300ohm balanced antenna but it also goes through the balun so I'm guessing the result will be the same.
The leakage from the caps was on the other side of the circuit, near the power supply and I did clean it up with alcohol.
Indeed I tried with a 75ohm basic T antenna and even on a strong station I had static and only average reception, I then just clipped a test lead on the other side of that balun coil and static was gone and signal strength way up (same happens if I touch the RF trimmer or clip my lead on there). I don't have a 300ohm balanced antenna but it also goes through the balun so I'm guessing the result will be the same.
The leakage from the caps was on the other side of the circuit, near the power supply and I did clean it up with alcohol.
"Silver mica disease " that's a new "internet fact " I know nothing about .
In 60 years of repairing all types of communications equipment that was full of silver mica capacitors of good or high quality none of them were shown to be faulty except the first earlier "uncovered " types in very old radios where chemicals/dirt etc got the better of them but that going back to the 1920,s/1930,s .
I only bought quality types manufactured in the UK at the time , I still have some unused .
For my future "learning " have you a link to this "disease " ?
What you are saying about the fault is typical of most radios that require a balanced input impedance that suites the RF section where a coil or other component develops a fault .
If you don't require the various inputs then you could install an inductance that matches the input impedance of the first stage to produce a stronger signal .
In post #2 I mentioned an ATU I made here is the same type (generally ) as the ones I built -- pretty simple and signal strength increased dramatically -
G4NSJ - ATU AMU aerial antenna tuning matching units - Radio WorkshopRadio Workshop
Of course you can buy now RF signal boosters using active devices or make one here is a circuit -
FM Signal Booster Circuit
In 60 years of repairing all types of communications equipment that was full of silver mica capacitors of good or high quality none of them were shown to be faulty except the first earlier "uncovered " types in very old radios where chemicals/dirt etc got the better of them but that going back to the 1920,s/1930,s .
I only bought quality types manufactured in the UK at the time , I still have some unused .
For my future "learning " have you a link to this "disease " ?
What you are saying about the fault is typical of most radios that require a balanced input impedance that suites the RF section where a coil or other component develops a fault .
If you don't require the various inputs then you could install an inductance that matches the input impedance of the first stage to produce a stronger signal .
In post #2 I mentioned an ATU I made here is the same type (generally ) as the ones I built -- pretty simple and signal strength increased dramatically -
G4NSJ - ATU AMU aerial antenna tuning matching units - Radio WorkshopRadio Workshop
Of course you can buy now RF signal boosters using active devices or make one here is a circuit -
FM Signal Booster Circuit
I was sure I answered but apparently not.
I checked and the silver mica disease I mentioned was indeed on way older gear so my bad.
I found a broken wire on the balun coil that I didn't see before and this fixed that issue but I now have a new one, the presets are off. They do stay stored well but if I tune to say 91Mhz, save it to preset 1, move the dial and then press the preset it moves but either to far or not far enough. No matter what frequency and preset number I use they are always slightly off centre. There is an alignment method described in the service manual but it uses and external centre meter which I don't have and the translation to english is very confusing. Is there an easy way to adjust these (with the upper and lower centre voltage adjustment pots)
I checked and the silver mica disease I mentioned was indeed on way older gear so my bad.
I found a broken wire on the balun coil that I didn't see before and this fixed that issue but I now have a new one, the presets are off. They do stay stored well but if I tune to say 91Mhz, save it to preset 1, move the dial and then press the preset it moves but either to far or not far enough. No matter what frequency and preset number I use they are always slightly off centre. There is an alignment method described in the service manual but it uses and external centre meter which I don't have and the translation to english is very confusing. Is there an easy way to adjust these (with the upper and lower centre voltage adjustment pots)