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Old 15th Jun 2010, 10:51 pm   #1
Dick Glennon
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Default Volume control in Pye P 74 (pye Ireland)

Hello again, When I turn on the radio I then start to turn up the volume control (seperate knob), When starting I have very clear sound, but very low . As I increase the volume it starts to make all sorts of squeals and whistles until I reach normal sound level and then it is ok again. The smoothing caps are alright as is the volume control, the valves and the speaker. All have been working on another radio similar to this one. This radio is similar to the P76F but has a magic eye as well. Any help would be appreciated. I have a circuit for the P76F. Regards Dick
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Old 15th Jun 2010, 11:05 pm   #2
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Default Re: Volume control in Pye P 74 (pye Ireland)

I haven't got a P74 on the list here, so I'm going off the P76F.

If the Volume Control is OK, I would go on a capacitor hunt. That capacitor needs changing if it's not been swapped already, as do any capacitors in series with the volume control. Using the Pye sheet, I would swap C33, C34, C35, R13, C37, R22.

Clean the volume control (Servisol and turn fast a few times) and make sure the contacts with the Pot itself are OK, You can use an AVO for this.

Cheers,

Steve P.
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Old 15th Jun 2010, 11:06 pm   #3
maitiustandun
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Default Re: Volume control in Pye P 74 (pye Ireland)

hello dick, i dont know your particular model, my set is the p57. have you tried cleaning the volumepot with serviceall 10?available at maplins.as a n aerosol.
if its not the volume control , has the tuning coils been messed with?what is the valve line up ?, is there long, medium , and shortwave on this set, and is the sqealing on all wavebands ? regards maitiu.
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Old 17th Jun 2010, 8:04 pm   #4
Dick Glennon
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Default Re: Volume control in Pye P 74 (pye Ireland)

Hi Lads, I have started to replace resistors and capacitors as you said, Valve lineup is EZ40, El 41, EBC41, EF 41, ECH 42 and magic eye. There are 7 wavebands plus pick-up. The noises are on all wavebands. Thanks Dick.
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Old 17th Jun 2010, 8:11 pm   #5
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Default Re: Volume control in Pye P 74 (pye Ireland)

Is it noisy on Pick-Up too? Are you sure it is the volume control and Audio area? Have you taken out and cleaned all the valve pins and sockets?

If the valves are in Parallel, then try removing the EF41 and then replacing it and taking out the ECH42. When do the noises go and when do they stay?

Noises does not mean a right lot. Is it hum, crackles, whistles. Is it all the time, on a station, off a station,,,,?

Cheers,

Steve P.
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Old 17th Jun 2010, 8:51 pm   #6
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Default Re: Volume control in Pye P 74 (pye Ireland)

Hello Dick

If your set is like the P76F, these have a HT supply for the ECH42 and EBC41 that is dropped down with from the main HT by a 4K7 resistor and decoupled with a 2uF electrolytic cap. If the 2uF cap is not working well, all sorts of motorboating and instability on all wavebands and Gram is the usual result. If your set has it, I'd suggest replacing this cap.

Hope this helps.


John
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Old 19th Jun 2010, 9:59 pm   #7
Dick Glennon
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Default Re: Volume control in Pye P 74 (pye Ireland)

Hello again, I have narrowed down the whistles and distortion to the EBC 41. When I take it out of its socket the distortion stops, but I loose all stations as well .The whistles are bad as I change the tone control, and the distortion comes on as I .turn up the volume. The volume also gets very loud in very little turning of the knob,but the distortion is not as bad. Hope you can help. Dick.
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Old 19th Jun 2010, 10:42 pm   #8
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Default Re: Volume control in Pye P 74 (pye Ireland)

Change the capacitor that jjl suggests.

Change the capacitors round the Volume and Tone controls Also C29.

Cheers,

Steve P.
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Old 20th Jun 2010, 7:35 pm   #9
Dick Glennon
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Default Re: Volume control in Pye P 74 (pye Ireland)

Hi, When I tested the volume control for continuety I found it was jumping maybe a couple of hundred ohms at a time, yet it works perfectly in another set. Dick.
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Old 20th Jun 2010, 8:38 pm   #10
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Default Re: Volume control in Pye P 74 (pye Ireland)

Are you using a digital or analogue meter? Analogue is best for testing volume controls!

Cheers,

Steve P.
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