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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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16th Sep 2006, 4:57 pm | #1 |
Octode
Join Date: Dec 2005
Location: Near Stowmarket, Suffolk, UK.
Posts: 1,962
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Pye P75- Strange noises
The other day I got another P75. The seller said it was working and after cleaning it out I tried it. It made a lot of squealing noises and a loud hum (altered by volume control) and I could hear Radio 4 in the background.
I changed two resistors and various capacitors (including the 16 & 32uF main smoothers). I now get a lot of thumping and squealing noises all over the dial. The stations are weak and can barely be heard above the squealing. However, 5-Live comes in loud and clear with no noises at all. Question is, how do I stop it squealing? I'll leave my other P75 (working, unrestored) in the workshop for now in case I need to compare anything. Any suggestions . Cheers, Josh. Last edited by Darren-UK; 30th Jul 2007 at 10:42 pm. Reason: General tidying. |
16th Sep 2006, 8:19 pm | #2 |
Dekatron
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
Posts: 7,549
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Re: Pye P75- Strange noises
Hi Josh.
My guess is that it is suffering from IF instability. I would suggest you change the wax capacitors decoupling the HT supply and screen grid of the IF amp and mixer...in fact if it was me, I would change all the old waxies anyway. You'll probably find this will solve a lot of problems. As you have another working set, you can try subbing the mixer and IF amp valves just in case one of them is causing the problem. Rich.
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16th Sep 2006, 8:22 pm | #3 |
Heptode
Join Date: Mar 2004
Location: Kendal, Cumbria, UK.
Posts: 623
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Re: Pye P75- Strange noises
Mine was exactly the same. Just needed the ht decoupling cap to the front end changing. Think it was a 2MFD electrolytic, but could be wrong Steve.
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16th Sep 2006, 8:24 pm | #4 |
Dekatron
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
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Re: Pye P75- Strange noises
I guess you've already done the obvious and replaced the audio coupling capacitor and checked the HT voltage is OK against the trader sheet? Does it do the same on gramaphone input? (assuming it's got one!)
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17th Sep 2006, 12:27 pm | #5 |
Octode
Join Date: Dec 2005
Location: Near Stowmarket, Suffolk, UK.
Posts: 1,962
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Re: Pye P75- Strange noises
I have already changed the waxies and I've changed two resistors. I'll try all the valves in a minute. It is possible it could be the 2uf capacitor. I'll swap it with my other one. Thanks for all advice so far. Josh.
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17th Sep 2006, 1:16 pm | #6 | |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,787
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Re: Pye P75- Strange noises
Quote:
In addition to everything others have mentioned, have a good look round for dislodged wiring around the wavechange switching and coils, and make sure the wavechange switch is clean. Good luck, Paul |
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17th Sep 2006, 4:46 pm | #7 |
Nonode
Join Date: Dec 2002
Location: Coulsdon, Surrey, UK.
Posts: 2,109
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Re: Pye P75- Strange noises
I had this problem on a P75 - It was down to the decoupler for the HF valve screen grids, which I think is the 2 mf cap mentioned. As it is shared across both valves, it seems that any inefficiencies due to leakage causes coupling between the stages and instability. Nice little sets when they're working.
Watch for poor contacts in the valve bases, they didn't appear of great quality in my set .... Andy |
19th Sep 2006, 4:48 pm | #8 |
Octode
Join Date: Dec 2005
Location: Near Stowmarket, Suffolk, UK.
Posts: 1,962
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Re: Pye P75- Strange noises
I temporarily fitted a 10uf 450v capacitor in and it worked fine. This is my second P75 and they are very good sets if you want a small fifties woodie. In fact they're good sets full stop! Josh.
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20th Sep 2006, 9:08 am | #9 |
Octode
Join Date: Aug 2003
Location: Welwyn Garden City, Herts. UK.
Posts: 1,906
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Re: Pye P75- Strange noises
HI Josh.
The P75RG has a larger value cap in this position presumably to reduce hum with the larger speaker so you could leave your 10uf in if you are not worried about authenticity Cheers Peter. |
20th Sep 2006, 10:05 am | #10 |
Octode
Join Date: Jan 2003
Location: Ware, Herts. UK.
Posts: 1,082
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Re: Pye P75- Strange noises
Josh
Good to hear that you fixed your problem. I've come across a number of Pye P76 sets where I needed to replace the electrolytic that decouples the supply to the 1st AF amp anode, IF screen grids and local oscillator anode. Symptoms were similar to your set; instability, howling, heavy distortion on bass notes etc. I believe that the P76 and P75 are similar if not identical in using this arrangement. John |