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Old 19th Aug 2007, 9:32 pm   #21
neil29
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Default Re: Decca Cs2230

hi tas.the capacitor is on the pl509 base wired in paralell with the resistor mentioned.cheers neil.
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Old 20th Aug 2007, 12:54 am   #22
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Default Re: Decca Cs2230

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simon. would you suggest changing the capacitor as well as it looks rather cooked.thanks neil.
That could be C434 the cathode decoupler, if you have checked this cap in situ it sits across a 6.8 or 10 ohme resistor. I would be reluctant to change out the screen feed resistor at this stage.
What voltages did you find on the control and screen grids? I might not be able to come back to you for a few days as I will be out on the town tomorrow night after work but hopefully will be recovered by Tues/Wed night.
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Old 20th Aug 2007, 12:57 am   #23
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Default Re: Decca Cs2230

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Originally Posted by Tazman1966 View Post
Hi Neil.

Drop me a PM with your address on it and I'll send you a photocopy of the compete manual and diagrams.

By the way, I had to replace the screen feed resistor on mine as it had fallen in half but was still electrically okay. I replaced it with a 9W version. Which capacitor are you talking about?

Hope to hear from you soon.
Funny mine did this as well, Being a 10 chassis it was a rather fiddly operation changing it under the valve base.
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Old 20th Aug 2007, 2:21 pm   #24
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Default Re: Decca Cs2230

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simon, the value of the resistor on the pl509 base has dropped to almost nothing,whilst the resistor on the sub panel has risen to just over 3k,bit of a daft question maybe but should i replace them as well as the capacitor.thanks neil.
Hi Neil.

When you say the value has dropped to almost nothing, do you mean it's gone all-but open circuit?

Thanks Neil.

From Mike.
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Old 19th Jan 2008, 4:10 pm   #25
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Default Re: Decca Cs2230

Hi all.last night i thought id have another go at this set.after previously changing the components metioned,and a couple of caps on the timebase panel. i switched on the set to find that as well as there being no change to the fault mentioned,another fault has developed.in so much as it can no longer be tuned in to a channel.basically it seems to pick up radio stations. and at first i thought i might have caused it by moving the panel about but theres no obvious breaks in any of the joints.and when i was checking various voltages,just after i put the the meter down something on the timebase panel decided to go pop. but did not see what component it was. so as usual im lost,again any help will be appreciated...cheers neil.
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Old 19th Jan 2008, 11:23 pm   #26
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Default Re: Decca Cs2230

It sounds like the line output stage is overheating. This results in a high voltage on the cathode of the PL509 being fed back to the IF AGC circuit via the beam limiting link. This shuts the IF stage down which results in shortwave stations around 6Mhz (49m band) being heard loud and clear.
The first thing I would do is do a visual of the timebase board to see what went pop, if nothing can be seen disconnect one end of the screen feed resistor to the PL509 to prevent any further overheating problems. With the set switched off do a DC check from the top cap of the PY500A to chassis. You should see just over 2M ohms. If its low prime suspects are the Boost Cap, the 5th harmonic tuning cap, the PY500A or shorted turns on the Lopty. If this reading is ok switch the set on and after warm up you should see more than -50v on the control grid of the PL509, if its low or missing then you have a line oscilator problem. If line drive is present and correct reconnect the screen feed resistor and disconnect the input to the tripler. If the line output stage now operates normally then you need a new Tripler.
Keep us updated of any developments.
I was locally known as the Bradford king in my younger days so if I can be of any further help please send me a pm.
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Old 20th Jan 2008, 10:33 pm   #27
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Default Re: Decca Cs2230

Thanks simon,ill do what you suggested.then ill let you know what exactly i find.cheers neil.
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Old 20th Jan 2008, 11:02 pm   #28
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Default Re: Decca Cs2230

Hello there.
Thinking back 30 odd years ,your problem rings a bell. Check that the thermal trip has not gone o/c. By this I mean the cathode connection for the PL509, which is fed through the trip on a third connection. If this goes o/c the cathode voltage of the PL509 increases and causes the cathode decoupler to explode. Might be worth a check. Good luck.
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Old 21st Jan 2008, 7:55 pm   #29
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Default Re: Decca Cs2230

Hi there Tellyman, I think this was an affliction for the early GEC single standard hybrid chassis. But if the PL509 cathode resistor goes o/c (thankfully rare) on any hybrid colour set then the decoupling cap would explode and the beam limiting circuit would burn.
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Old 22nd Jan 2008, 5:25 pm   #30
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Default Re: Decca Cs2230

Simon,ive checked the PY500 top cap to chassis as you suggested but did not get any reading at all.ive also checked a couple of resistors mentioned on dominics thread. and R444 reads 38k.and R453 reads 597k.also theres been a bit of a burn up on the timebase panel as can be seen in the picture do you think its worth checking the other components mentioned or should i replace the resistors and the PY500 and hope for the best.cheers neil..
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Old 22nd Jan 2008, 6:26 pm   #31
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Default Re: Decca Cs2230

Hi all. after changing the resistors mentioned.and swapping the PY500.it no longer seems to immitate a radio.basically you have the normal hissing sound (when it is not tuned in).but ive also noticed that the cathode decoupler has blown(probably the popping sound i heard)would anyone think putting a new cap in would sort it out or do i have to replace a few more bits first..thanks neil..
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Old 25th Jan 2008, 10:41 pm   #32
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Default Re: Decca Cs2230

Hi Neil, I would certainly change out the cathode decoupler capacitor. Looking at that picture of those burnt/damaged tracks on the T/B board I would check/repair these, and by mapping out what the tracks feed attempt to see what caused this damage.
A few times we had earthing problems that caused a burn up around the frame output stage, I suppose the same could happen for the line output stage as well.
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Old 25th Jan 2008, 10:52 pm   #33
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Default Re: Decca Cs2230

Hi simon,funnily enough i did change the cap and resistor,o/c. the other day.and it popped again,although this time with one hell of a bang.foil everywhere,the can flew out narrowly missing me.and lots of smoke.but ill do what you suggested and check everything connected to that area,as well as earths etc. thanks again neil.
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Old 26th Jan 2008, 9:58 pm   #34
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Default Re: Decca Cs2230

What voltage are you getting across that cap, I would check before you replace it again. It might give you a bit of a clue as to what is going on.
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Old 27th Jan 2008, 9:17 pm   #35
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Default Re: Decca Cs2230

Hi Neil.
I still stand by the suggestion in my post above, check the cut out unit. the one used in this set has a third connection which as I remember was used as the cathode connection for the PL509. If the lop stage overheated it caused the cut out to operate. I had this connection fail a number of times causing the fault you describe.
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Old 31st Jan 2008, 1:12 pm   #36
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Default Re: Decca Cs2230

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Originally Posted by tellyman View Post
Hi Neil.
I still stand by the suggestion in my post above, check the cut out unit. the one used in this set has a third connection which as I remember was used as the cathode connection for the PL509. If the lop stage overheated it caused the cut out to operate. I had this connection fail a number of times causing the fault you describe.
Hi Tellyman
I may stand to be corrected, but the only cuttout arrrangements that I have seen on the Decca Bradford was the MK1 10 chassis where the cuttout was in effect both the mains fuse and the LT fuse. I think they bought the cuttout back on the final Bradford chassis but I am sure it was just a single pair of contacts replacing the mains fuse.
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