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Old 26th Feb 2015, 9:49 pm   #1
McMurdo
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Default Baird 258 FM distorted and quiet

I've got a Baird 258 here I thought I'd have a look at after getting it last year.

I've fitted all new electrolytics (this set runs hot and the smoothing block was o/c), checked all resistors (3 or 4 out of tol) and cleaned the valve pins. I'm hoping to make this my new kitchen set.

AM bands work just great and a lovely loud sound and good reception from the rod aerial.

But FM is very quiet and rather distorted. I have to turn the volume up to full to make it useable. Any chance the FM board is out of alignment? I can't find service info anywhere, though another thread suggests there's a radiogram with similar radio chassis.

Lineup is a pretty standard UL84 UABC80 UF89 UCH81 UCC85 and a rectifier.

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Old 26th Feb 2015, 10:50 pm   #2
Herald1360
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Default Re: Baird 258 FM distorted and quiet

The Baird M238 looks like it could use the same chassis.

http://www.service-data.com/product.php/361/670/m10361
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Old 26th Feb 2015, 11:28 pm   #3
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Default Re: Baird 258 FM distorted and quiet

thanks chris yes it looks the same, I'd never have found that!
I've just found another UCC85 to try first, just in case.
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Old 26th Feb 2015, 11:33 pm   #4
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Default Re: Baird 258 FM distorted and quiet

The UABC80 will use 2 of the diodes as FM detector if you have one to try.
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Old 27th Feb 2015, 12:48 am   #5
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Default Re: Baird 258 FM distorted and quiet

Quote:
Originally Posted by McMurdo View Post
thanks chris yes it looks the same, I'd never have found that!
I just looked up Baird in RM picked one with the same valve lineup and its general layout looked similar.......

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Old 27th Feb 2015, 11:19 am   #6
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Default Re: Baird 258 FM distorted and quiet

Well worth a read.http://www.vintage-radio.com/recent-...baird-301.html.
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Old 27th Feb 2015, 11:47 am   #7
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Default Re: Baird 258 FM distorted and quiet

Hi Kevin

I know you have stated that you have replaced all the electrolytic capacitors but the small one in the FM detector is easy to miss and critical to good FM performance. It is C44 in the Baird manual mentioned by Chris and a modern 4.7uF 25v will do.

If you have replaced that capacitor and tried a new UABC80 and you still have the symptom try this before you attempt a full FM alignment. The secondary of the last FM I.F transformer can go slightly off tune causing this symptom. In the Baird manual the secondary of T8 is (incorrectly) not marked as adjustable but in the alignment instructions it is indicated as the bottom core of T8. Try a small readjustment to this core before you resort to a full alignment. You can always put it back where it was if it doesn't correct the problem.
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Old 27th Feb 2015, 1:21 pm   #8
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Default Re: Baird 258 FM distorted and quiet

And, no need to remind you, Kevin, that the 5uF cap Colin mentions is generally wired with the +ve lead to chassis.

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Old 27th Feb 2015, 8:50 pm   #9
McMurdo
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Default Re: Baird 258 FM distorted and quiet

I changed all electrolytics, though there are only really a handful in the set. I always mark the pcb with a black marker dot to negative.
Today I found a UABC80, changed it, made no difference. Then I changed the UCC85 which simply made the problem much worse with the programme being barely audible. I suspect that valve may be duff, it's just one from my stores.
As well as distorted and quiet, it's also knife-edge critical to tune and it fades like mad when moving my hand anywhere near the aerial (which is just a loop of wire for the moment). I'll see if I can find a NOS UCC85.

PS I'm impressed with the audio volume and quality on R4 LW. There's lots of deep rich sound from the little Fane speaker..and that's even with the back off the cabinet! I'm dying to hear it working properly on FM.
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