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Old 14th Aug 2018, 4:41 pm   #1
regentone001
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Default Regentone Ten-17

Hi
having become fed up with the poor sound on this set I found that when I re capped it I had missed one. Replacing it brought up the sound but also a hum. The hum varies with the picture content,it isn't a buzz like vision on sound it is a definite hum. If I turn the fine tuner until the picture breaks up the hum goes, I can also get rid of most of it by turning down the contrast, but then the picture becomes unstable. Having found one dry joint, been like it since the set was made, I am wondering if it is another dry joint causing the hum problem.
Sometimes there is also a band of faint shadow across the picture and also at times a band of brighter picture for about an inch from the top of the picture. Are these all related as they seem to be and caused by the same thing.
Thanks
Steve
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Old 14th Aug 2018, 4:51 pm   #2
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Default Re: Regentone Ten-17

Which capacitor did you change? In what part of the circuit is it, I.F. side or audio. J.
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Old 14th Aug 2018, 5:14 pm   #3
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Default Re: Regentone Ten-17

It sounds as though there is ripple or hum on the DC Supply to the tuner & IF section of the set. The fact that the hum decreases with reduction in the contrast control suggests there is mains hum amplitude modulation on the power supply feed to the RF circuitry and is manifest on the detected video (with the brighter area you see) and is getting into the sound channel. When it tunes off the station the IF signal level drops along with the hum modulation. Also, it would be normal that it might lose sync with low contrast, depending on where in the set the designers chose to to pick off the sync.

Most likely it's not a dry joint, but hum could be introduced into the video or audio IF by heater-cathode leakage too as another option of how hum could get into the signal circuits, but possibly more likely by poor electrolytic caps filtering the supply rails.

Without being familiar with the exact circuit, it's guessing. Going over it with the scope would give the game away as to what the cause was.
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Old 14th Aug 2018, 6:28 pm   #4
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Default Re: Regentone Ten-17

Hi J
the cap I replaced was in the audio stages C64 in the attached circuit extract

Hi Argus thanks I will have to check the smoothing and reservoir caps I replaced and make sure they are ok
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Old 14th Aug 2018, 8:35 pm   #5
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Default Re: Regentone Ten-17

Check or replace all the components marked as: *

Leaky coupling capacitors C61, C62 and C66 will cause distortion.
Cathode bias resistor R76 might have changed in value.

DFWB.
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Old 16th Aug 2018, 1:35 pm   #6
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Default Re: Regentone Ten-17

Hi Fernseh
I had already replaced all those caps when I recapped the set originally and have replaced the bias resistor.
I have checked the smoothing and reservoir caps and in fact have higher capacity than originally specified to counter act the mains ripple.
I have tried replacing all the valves, in case one had a heater cathode short all to no avail,though I did find I had two duff 30pl13s.
I think that the fault was there from the time I got the set but wasn't apparent on the sound as it was not very loud and quite thin with very little bass. Replacing C64 brought up the vol and also the bass. The effect on the picture is not always apparent on the test card it is hardly noticeable at all. I am thinking of trying the crt with a transformer supply to the heater,I have several around from old radios that have 6.3v windings but if that cures it would then have to get a small one to mount in the set. If not I will have to remove the printed panel and go over the whole thing checking for shorts.
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Old 16th Aug 2018, 5:27 pm   #7
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Default Re: Regentone Ten-17

I think the problem was most likely there too , but became obvious when the bass response improved.

It's fairly certain that the hum you are hearing is modulating the amplitude of the signal carrier at and prior to the audio detector, otherwise it would not go away when you tuned off station. When that happens the carrier and the hum modulation on it approaches zero .

If the problem was anywhere in the area of the first audio amp, noise limiter diode or audio output amp the hum would not go away when you tuned off station.

Can you attach the video and audio IF and tuner circuit ?

What happens to the hum when you either disconnect or short out the signal output from the tuner ?
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Old 16th Aug 2018, 5:45 pm   #8
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Default Re: Regentone Ten-17

well I was just going to do some voltage checks and the valves lit but no HT. the rectifier diode had popped its clogs (originalSTC FST1/4). What can I use to replace it?

Argus I will scan the iFs later and attach them
Steve
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Old 16th Aug 2018, 8:39 pm   #9
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Default Re: Regentone Ten-17

The STC FST1/4 is a 400 volt 0.5 A
1N4007 is a suitable replacement
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Old 16th Aug 2018, 9:01 pm   #10
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Default Re: Regentone Ten-17

thanks Stephen
cooo ain't they expensive? £1.69 for 50 including postage lol
Steve
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Old 20th Aug 2018, 1:27 pm   #11
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Default Re: Regentone Ten-17

well the rectifiers arrived today so will see about replacing it. Originally,according to the circuit diagram, there should have been two in series should I replace them like that? There was only one in the set when I got it where the other should have been had been bridged out.

Argus
please see attached scans of I.Fs
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Old 20th Aug 2018, 2:11 pm   #12
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Default Re: Regentone Ten-17

Hi Argus well I tried shorting out the if output from the tuner and the sound came up clearer without the hum and the picture broke up a bit with sound on vision. It also cut down the brightness
Steve
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Old 3rd Sep 2018, 3:19 pm   #13
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Default Re: Regentone Ten-17

with no joy I decided to take out the printed circuit board and check it out. I then decided to rather than do that remove the one from the TEN-6FM I have,which needs work on the lopt, check the components and then put that board into the TEN-17. I have replaced all of the resistors, only a couple were anywhere near the tolerance they should be. I am just waiting for a couple more to arrive then that will be completed. I have also replaced the wax caps. Hopefully when I fit this board it will cure the problem. Then I can work on the original board ready to go back into the TEN-6FM. There are just a couple of differences between the boards ,one resistor isn't fitted on the board but on the TV/FM switch on the Ten-6 and a wire link is removed from the board again on the TEN-6 for operation of the switch from TV to FM
Steve
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Old 15th Sep 2018, 1:14 pm   #14
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Default Re: Regentone Ten-17

I scrubbed the top,print side, of the board using neat Flash which removed most of the dirt and grease, where the grease came from I have no idea. I basically rebuilt the board replacing all of the resistors and most of the caps,a lot of the ceramic ones were looking charred so out they came, and for what it cost it was worth doing while access to the board was the best it could be.
Fitted it into the TEN-17 and the results are excellent. Sound is much better no hum and a full sound not shrieky and the test card even the 5mhz bars are easy to see,though unfortunately not visible in the photo. I have a suspicion that some of the caps I replaced on the original board even though new are actually c**p.I will see when I rebuild that board. I am now giving the board from my 17-18 the rebuild treatment. Though on this one I will also replace the valve holders as I have had trouble with some of them before.
I must admit to having a hankering to make a completely new circuit board,in the original Regentone manuals they give a layout print which would be easy to adapt and the board is just a fraction larger than the layout diagram but would be easy to enlarge to the correct size but I don't have the means to print and etch
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